Unit 4 (Week 13 Patterns of Inheritance) Flashcards
What is the transmission of characteristics from parent to offspring?
Inheritance
What was the idea that the determinants of hereditary traits are transmitted in discrete units, or particles, from one generation to the next?
Particular inheritance
[Information on Different Types of Mendelian Inheritance Patterns and Their Molecular Basis]
Simple Mendelian inheritance
Inheritance pattern: Pattern of traits is determined by a pair of alleles that display a dominant/recessive relationship and are located on an autosome. The presence of the dominant allele masks the presence of the recessive allele.
Molecular basis: In many cases, the recessive allele is nonfunctional. Though a heterozygote may produce 50% of the functional protein compared with a dominant homozygote, this is sufficient to produce the dominant trait.
X-linked inheritance
Inheritance pattern: Pattern of traits is determined by genes that display a dominant/recessive relationship and are located on the X chromosome. In mammals and fruit flies, males are hemizygous for X-linked genes. In these species, X-linked recessive traits occur more frequently in males than in females.
Molecular basis: In a female with one recessive X-linked allele (a heterozygote), the protein encoded by the dominant allele is sufficient to produce the dominant trait. A male with a recessive X-linked allele does not have a dominant allele and does not make any of the functional protein.
Incomplete dominance
Inheritance pattern: Pattern that occurs when the heterozygote has a phenotype intermediate to the phenotypes of the homozygotes, as when a cross between red-flowered and white-flowered plants produces pink-flowered offspring.
Molecular basis: Fifty percent of the protein encoded by the functional (wild-type) allele results in an intermediate phenotype.
Codominance
Inheritance pattern: Pattern that occurs when the heterozygote expresses both alleles simultaneously. For example, a human carrying the A and B alleles for the ABO antigens of red blood cells produces both the A and the B antigens (has an AB blood type).
Molecular basis: The codominant alleles encode proteins that function somewhat differently from each other. In a heterozygote, the function of each protein affects the phenotype uniquely.
Epistasis
Inheritance pattern: A type of gene interaction in which the alleles of one gene mask the effects of an allele of another gene.
Molecular basis: Two different genes are needed to produce a given phenotype. Loss of function of one of the genes alters the phenotype.
Continuous variation
Inheritance pattern: A pattern in which the offspring display a continuous range of phenotypes.
Molecular basis: This pattern is produced by the additive interactions of several genes, along with environmental influences.
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[Start 17.1 Mendel’s Laws of Inheritance]
In 1856, Gregor Mendel began his historic studies on what plant?
How long did he analyze this plant?
What was the name of his published paper in 1866?
Why was his paper ignored by peers?
Pea plants.
8 years!
“Experiments on Plant Hybrids”
His paper was largely ignored because of the title.
What is the process in which two individuals of the same species with different characteristics are bred or crossed to each other; the offspring are referred to as hybrids?
Hybridization
What was Mendel particularly intrigued by?
The consistency with which offspring of such crosses (different characteristics of plants in the same species) showed characteristics of one or the other parent in successive generations.
How did Mendel, with a foundation in physics and natural sciences, lead him to uncover the naturals laws governing inheritance?
He carried out quantitative experiments in which he carefully analyzed the numbers of offspring carrying specific traits.
What is a characteristic of an organism, such as the appearance of seeds, pods, flowers, or stems in the garden pea?
Called a character.
Why did he choose this species? Several properties of the garden pea were particularly advantageous for studying inheritance. First, it was available in many varieties that differed in characteristics.
What is an identifiable characteristic; usually refers to a variant?
Trait
What was another advantage of studying the pea plant?
They are normally self-fertilizing.
What is fertilization that involves the union of a female gamete and male gamete from the same individual?
Self-fertilization
What is a strain that continues to exhibit the same trait after several generations of self-fertilization or inbreeding?
True-breeding line
What was the third reason why pea plants were used in hybridization experiments?
Ease of making crosses: The flowers are fairly large and easy to manipulate. In some cases, Mendel wanted his pea plants to self-fertilize, but in others, he wanted to cross plants that differed with respect to some character, a process called hybridization, or cross-fertilization.
What is cross fertilization?
Fertilization that involves the union of a female gamete and a male gamete from different individuals.
Why are the stamens removed from the purple flower in this cross-fertilization procedure?
The stamens are removed from the purple flower to prevent self-fertilization.
What is a cross in which an experimenter follows the variants of only one character?
Single-factor cross
As an example, we will consider a single-factor cross in which Mendel followed the tall and dwarf variants for height
What does P generation mean?
The parental generation in a genetic cross.
What does F1 generation mean?
The first generation of offspring in a genetic cross.
What is the The F1 offspring, also called single-trait hybrids, of true-breeding parents that differ with regard to a single character?
A monohybrid.
Why do offspring of the F1 generation exhibit only one variant of each character?
The reason why offspring of the F1 generation exhibit only one variant of each character is because one trait is dominant over the other.
How is the second generation of offspring in a genetic cross denoted?
F2 generation
What was the three important ideas that Mendel postulated about the properties of traits and their transmission from parents to offspring?
- Traits may exist in two forms, dominant and recessive.
- An individual carries two genes for a given character, and genes have variant forms (now called alleles).
- The two alleles of a gene separate during the process that gives rise to haploid cells and gametes, so each sperm and egg receives only one allele.
What are the alternative traits described as?
Dominant and recessive
What refers to the trait that is displayed in a heterozygote?
Dominant
What refers to a trait that is masked by the presence of a dominant trait in a heterozygote?
Recessive
Tall stems and purple flowers are examples of dominant traits; dwarf stems and white flowers are examples of recessive traits. In this case, we say that tall is dominant over dwarf, and purple is dominant over white.
What is a unit of heredity?
A gene. At the molecular level, a gene is an organized unit of base sequences in a DNA strand that can transcribed into RNA and ultimately results in the formation of a functional product.
What coined the word gene?
A term coined by the Danish botanist Wilhelm Johannsen in 1909. Comes from the Greek word, genos, meaning birth.
What did Mendel postulate about genes?
Mendel postulated that every individual carries two genes for a given character and that the gene for each character in his pea plants exists in two variant forms, which we now call alleles.
What did Mendel always observe via a ratio in dominant and recessive traits?
3:1 ratio.
How did Mendel interpret this ratio? He concluded that each F1 plant carried two versions (alleles) of a gene affecting height (or another character) and that the two alleles carried by such an F1 plant separate, or segregate, from each other during the process that gives rise to gametes.
Therefore, each sperm or egg carried only one allele.
Remember: Tt combinations, or dominant-recessive combination of gametes, can occur in two different combinations. This means the dominant trait can come from the egg or the sperm.
This also means that Tt offspring are produced twice as often as TT or tt offspring.
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Which law states: The two alleles of a gene separate (segregate) from each other during the process that gives rise to gametes, so every gamete receives only one allele?
Mendel’s law of segregation
What is the ratio of the T allele to the t allele in the F2 generation? Does this ratio differ from the 3:1 phenotype ratio? If so, explain why.
The ratio of alleles (T to t) is 1:1. The reason why the phenotypic ratio is 3:1 is because T is dominant to t.
What is the genetic composition of an individual?
The genotype.
[Use Picture Mendel’s Analysis] TT and tt are the genotypes of the P generation, and Tt is the genotype of the F1 generation. In the P generation, both parents are true-breeding plants, which means that each has identical copies of the allele of the gene for height.
What do you call an individual with two identical copies of an allele?
What about an individual with two different alleles of the same gene?
Homozygous
In the specific cross we are considering, the tall plant (TT) is homozygous for T, and the dwarf plant (tt) is homozygous for t.
Heterozygous
Plants of the F1 generation are heterozygous, with the genotype Tt, because every individual carries one copy of the tall allele (T) and one copy of the dwarf allele (t). The F2 generation includes both homozygous individuals (homozygotes) and heterozygous individuals (heterozygotes).
What is the characteristics of an organism that are the result of the expression of its genes?
Phenotype.
Although the F1 offspring are heterozygous (Tt), they are phenotypically tall because each of them has a copy of the dominant tall allele. In contrast, the F2 plants display both phenotypes in a ratio of 3:1.
What is a common method for predicting the outcome of simple genetic crosses?
What are the steps to do a Punnett square? (5)
A Punnett square, developed by British geneticist Reginald Punnett
- Write down the genotypes of both parents. In this example, a heterozygous tall plant is crossed to another heterozygous tall plant. The plant providing the pollen is considered the male parent and the plant providing the eggs, the female parent. (In self-pollination, a single individual produces both types of gametes.)
Male parent: Tt
Female parent: Tt
- Write down the possible gametes that each parent can make. Remember the law of segregation tells us that a gamete contains only one copy of each allele.
Male gametes: T or t
Female gametes: T or t
- Create an empty Punnett square. The number of columns equals the number of male gametes, and the number of rows equals the number of female gametes. Our example has two rows and two columns. Place the male gametes across the top of the Punnett square and the female gametes along the side. (Outside the box)
Step 4. Fill in the possible genotypes of the offspring by combining the alleles of the gametes in the empty boxes.
Step 5. Determine the relative proportions of genotypes and phenotypes of the offspring. The genotypes are obtained directly from the Punnett square. In this example, the genotype ratio is 1 TT : 2 Tt : 1 tt. To determine the phenotypes, you must know which allele is dominant. For plant height, T (tall) is dominant to t (dwarf). The genotypes TT and Tt are tall, whereas the genotype tt is dwarf. Therefore, our Punnett square shows us that the phenotype ratio is expected to be 3 tall : 1 dwarf.
- What can we conclude if an individual has a recessive phenotype?
- What about if an individual has a dominant phenotype?
- It is homozygous for the recessive allele.
In this example, a plant that is dwarfed in height, has a genotype of tt which means it is homozygous for the recessive allele.
- An individual with a dominant phenotype may be either homozygous or heterozygous—a tall pea plant may have the genotype TT or Tt.
How do we distinguish between the two possibilities of a individual’s genotype (either having all dominant, TT alleles or heterozygous allele Tt) who has a dominant phenotype?
Mendel devised a method called a testcross to address this question. In a testcross, the researcher crosses the individual of interest to a homozygous recessive individual and observes the phenotypes of the offspring.
Essentially, a cross to determine if an individual with a dominant phenotype is a homozygote or a heterozygote.
Let’s suppose you had a pea plant with purple flowers and unknown genotype and conducted a testcross to determine its genotype. You obtained 41 offspring plants: 20 with white flowers and 21 with purple flowers. What was the genotype of the original purple-flowered plant?
The genotype was Pp. To produce white offspring, which are pp, the original plant had to have at least one copy of the p allele. Because it had purple flowers, it also had to have one copy of the P allele. So, its genotype must have been Pp.
What is a cross in which an experimenter simultaneously follows the inheritance of two different characters?
Two-factor cross
In two-factor crosses, if link assortment would have been correct, what would be the outcome of a F2 generation? Use the F1 generation of YyRr.
The gametes’ genotypes in the P generation are YR and yr.
If alleles of genes are linked, we cannot have any new combinations meaning that the Punnett square would be:
YR yr for the sperm
YR yr for the eggs
YYRR, YyRr, YyRr, and yyrr is the result of the Punnett square.
Yellow seeds would always be round and wrinkled seeds would always be green with a 3:1 ratio.
Since these alleles of genes are linked, new combinations cannot be created.
This hypothesis was proven incorrect a one point, but there are cases where genes are expressed in pairs therefore creating a link.
What is the hypothesis that proved the linked assortment incorrect?
Independent assortment allows for more combinations of alleles in genes independent of any linkage.
If the two genes are linked, the F1 plants could produce gametes that are only YR or yr. These gametes would combine to produce offspring with the genotypes YYRR (yellow, round), YyRr (yellow, round), and yyrr (green, wrinkled). The ratio of phenotypes would be 3 yellow, round to 1 green, wrinkled. Every F2 plant would be phenotypically like one P-generation plant or the other. None would display a new combination of the parental traits.
However, if the alleles assorted independently, the F2 generation would have a wider range of genotypes and phenotypes.
In this case, the columns and rows will have more combinations since YR and yr are not linked alleles in genes. The example in the book went from YR and yr for both eggs and sperm to TY, Yr, yR, and yr for both eggs and sperm.
In this case, each F1 parent produces four kinds of gametes—YR, Yr, yR, and yr—instead of two, so the square is constructed with four rows on each side and shows 16 possible genotypes. The F2 generation includes plants with yellow, round seeds; yellow, wrinkled seeds; green, round seeds; and green, wrinkled seeds, in a ratio of 9:3:3:1.
What refers to an offspring that is a hybrid with respect to two traits?
Dihybrid
What is the second law of Mendel’s work that states: “The alleles of different genes assort independently of each other during the process that gives rise to gametes.”?
Mendel’s law of independent assostment
[Start 17.2 The Chromosome Theory of Inheritance]
Who addressed that a substance in living cells is responsible for the transmission of hereditary traits?
August Weismann and Karl Nageli in 1883.
This idea challenged other researchers to identify the genetic material. Several scientists, including German biologists Eduard Strasburger and Walther Flemming, observed dividing cells under the microscope and suggested that the chromosomes are the carriers of the genetic material. As we now know, the genetic material is the DNA within chromosomes.
What is an explanation of how the steps of meiosis account for the inheritance patterns observed by Mendel?
What are the fundamental principles? (5)
Chromosome Theory of Inheritance
1. Chromosomes contain DNA, which is the genetic material. Genes are found within the chromosomes. 2. Chromosomes are replicated and passed from parent to offspring. They are also passed from cell to cell during the development of a multicellular organism. 3. The nucleus of a diploid cell contains two sets of chromosomes, which are found in homologous pairs. The maternal and paternal sets of homologous chromosomes are functionally equivalent; each set carries a full complement of genes. 4. At meiosis, one member of each chromosome pair segregates into one daughter nucleus, and its homolog segregates into the other daughter nucleus. During the formation of haploid Page 356cells, the members of different chromosome pairs segregate independently of each other. 5. Gametes are haploid cells that combine to form a diploid cell during fertilization, with each gamete transmitting one set of chromosomes to the offspring.
What is the physical location of a gene on a chromosome?
Locus or loci for plural
[Bonus] If two chromosomes are homologous (similar in position, structure, and evolutionary origin but not necessarily in function), can they still be if each chromosome has a different allele, TT and tt, in their loci?
Yes, because they are the same in structure just not in function.
Explain the relationship between the chromosome theory of inheritance and Mendel’s law of segregation.
Two homologous chromosomes prior to DNA replication.
When a cell prepares to divide, the homologs replicate to produce pairs of sister chromatids. Each chromatid carries a copy of the allele found on the original homolog, either T or t.
During meiosis I, the homologs, each consisting of two sister chromatids, pair up and then segregate into two daughter cells. One of these cells has two copies of the T allele, and the other has two copies of the t allele. The sister chromatids separate during meiosis II, which produces four haploid cells. The end result of meiosis is that each haploid cell has a copy of just one of the two original homologs. Two of the cells have a chromosome carrying the T allele, and the other two have a chromosome carrying the t allele at the same locus.
How can we relate the chromosome theory of inheritance to Mendel’s law of independent assortment?
The alleles for seed color (Y or y) and seed shape (R or r) in peas are on different chromosomes (4 individual chromosomes). During metaphase of meiosis I, different arrangements of the two chromosome pairs lead to different combinations of the alleles in the resulting haploid cells.
On the left, the chromosome carrying the recessive y allele has segregated with the chromosome carrying the dominant R allele. On the right, the two chromosomes carrying the dominant alleles (Y and R) have segregated together. Note: For simplicity, this diagram shows only two pairs of homologous chromosomes, though eukaryotic cells typically have several different pairs of homologous chromosomes.
[Extra Information]
When meiosis begins, the DNA in each chromosome has already replicated, producing two sister chromatids. At metaphase I of meiosis, the two pairs of chromosomes randomly align themselves along the metaphase plate. This alignment can occur in two equally probable ways, shown on the two sides of the figure. On the left, the chromosome carrying the y allele is aligned on the same side of the metaphase plate as the chromosome carrying the R allele; Y is aligned with r. On the right, the opposite has occurred: Y is aligned with R, and y is with r. In each case, the chromosomes that aligned on the same side of the metaphase plate segregate into the same daughter cell. In this way, the random alignment of chromosome pairs during meiosis I leads to the independent assortment of alleles found on different chromosomes. For two genes found on different chromosomes, each with two variant alleles, meiosis produces four allele combinations in equal numbers (yR, Yr, YR, and yr), as seen at the bottom of the figure.If a YyRr (dihybrid) plant undergoes self-fertilization, any two gametes can combine randomly during fertilization. Because four kinds of gametes are made, 42, or 16, possible allele combinations are possible in the offspring. These genotypes, in turn, produce four phenotypes in a 9:3:3:1 ratio .This ratio is the expected outcome when a heterozygote for two genes on different chromosomes undergoes self-fertilization.
Let’s suppose that a cell is heterozygous for three different genes (Aa, Bb, and Cc) and that each gene is on a different chromosome. How many different ways can the three pairs of homologous chromosomes align themselves during metaphase I, and how many different types of gametes can be produced?
There are four possible ways that the chromosomes can align, and eight different types of gametes (ABC, abc, ABc, abC, Abc, aBC, AbC, aBc) can be produced.
[Start 17.3 Pedigree Analysis of Human Traits]
Why can geneticists not use the approach of what was done on peas to be used on humans?
For ethical and practical reasons.
What is an examination of human traits over several generations in a family as a way to deduce the pattern of inheritance?
Pedigree analysis
The results of this method may be less definitive than the results of breeding experiments because the small size of human families may lead to large sampling errors. Nevertheless, a pedigree analysis often provides important clues concerning human inheritance.
What two forms do many genes play a role in exist as?
The common allele and a rare allele that has arisen by mutation.
What does pedigree analysis allow us to determine?
Whether the mutant allele is dominant or recessive and to predict the likelihood of an individual being affected.
- What is a genetic disease which involves a mutation in a gene that encodes the cystic fibrosis transmembrane regulator (the CTFR gene)?
- How many Americans of European descent are heterozygous carries of the recessive (disease causing) CFTR allele?
- Who exhibits symptoms of this disease?
- In the human pedigree, how are oldest to newest generations denoted in the modeling?
- What is represented by squares, circles, horizontal and vertical lines?
- Cystic fibrosis (CF)
- 3%
- Individuals who are homozygous for this allele exhibit the disease symptoms, which include abnormalities of the lungs, pancreas, intestine, and sweat glands.
- Roman numerals. I denotes oldest while III would denote newest so on so forth. II would denote middle generation.
- Males are squares, women are circles, horizontal lines directly connecting shapes are mates, vertical lines attached to horizontal lines denote offspring. If shapes are branched off the same horizontal line, they are siblings. Direct connections are only for mates.
Filled shapes are affected, half-filled shapes are presumed heterozygous, and empty shapes are unaffected individuals
Let’s suppose a genetic disease is caused by a mutant allele. If two affected parents produce an unaffected offspring, can the mutant allele be recessive?
No. If two parents are affected with the disease, they would have to be homozygous for the mutant allele if it’s recessive. Two homozygous parents would produce all affected offspring, barring rare mutations. If they produce an unaffected offspring, then the mutant allele is not recessive.
Why does the pedigree indicate a recessive pattern of inheritance for CF?
The answer is that two unaffected individuals can produce an affected offspring. Such individuals are presumed to be heterozygotes (designated by a half-filled symbol).
However, the same unaffected parents can also produce unaffected offspring (depicted by an unfilled symbol), because an individual must inherit two copies of the mutant allele to exhibit the disease.
A recessive mode of inheritance is also indicated by the observation that all of the offspring of two affected individuals are affected themselves. However, for genetic diseases that limit survival or fertility, there are rarely if ever cases where two affected individuals produce offspring.
T/F Most alleles causing human genetic diseases are recessive, but some are known to be dominant.
True.
What is a disease whereas the condition that causes the degeneration of brain cells involved in emotions, intellect, and movement?
Huntington disease.
When does Huntington appear and what specific symptoms are there?
30 to 50 years old, and includes uncontrollable jerking movements of the limbs, trunk, and face; progressive loss of mental abilities; and the development of psychiatric problems.
What observation in a pedigree suggests a dominant pattern of inheritance?
All affected offspring having at least one affected parent suggests a dominant pattern of inheritance.
However, affected parents do not always produce affected offspring. For example, II-6 is a heterozygote that has passed the nondisease-causing allele to his offspring, thereby producing unaffected offspring (III-3 and III-4).
Where are most human genes found?
On paired chromosomes called autosomes, these exclude the sex chromosomes.
Huntington disease is an example of a trait with an autosomal dominant inheritance pattern, whereas cystic fibrosis displays an autosomal recessive pattern. However, some human genes are located on sex chromosomes, which are different in males and females. These genes have their own characteristic inheritance patterns
[17.4 Sex Chromosomes and X-Linked Inheritance Patterns]
What is a distinctive pair of chromosomes that are different in males and females of some species and determine the sex of an individual?
Sex chromosomes
Sex chromosomes are found in many but not all species with two sexes.
If a person is born with only one X chromosome and no Y chromosome, would you expect that person to be a male or a female?
The person is a female. In mammals, the presence of the Y chromosome causes maleness. Therefore, lacking a Y chromosome, a person with a single X chromosome develops into a female.
What gene located on the Y chromosome of mammals plays a key role in the developmental pathway that leads to maleness?
The SRY gene
The X-Y System operates in mammals.
Where does the X-O system operate in and how does it differ from the X-Y system?
It operates in insects.
THe Y chromosome does not determine maleness.
Females in this system have a pair of sex chromosomes and are designated XX. In some insect species that follow the X-O system, the male has only one sex chromosome, the X. In other X-O insect species, such as Drosophila melanogaster, the male has both an X chromosome and a Y chromosome. In all cases, an insect’s sex is determined by the ratio between its X chromosomes and its sets of autosomes.
If a fly has one X chromosome and is diploid for the autosomes (2n), this ratio is 1/2, or 0.5. This fly will become a male whether or not it receives a Y chromosome. On the other hand, if a diploid fly receives two X chromosomes, the ratio is 2/2, or 1.0, and the fly becomes a female.
For birds and some fish, the Z-W system operates how?
Thus far, we have considered examples where females have two similar copies of a sex chromosome, the X. However, in other animal species, such as birds and some fish, the male carries two similar chromosomes. This is called the Z-W system to distinguish it from the X-Y system found in mammals. The male is ZZ, and the female is ZW.
What system does not involve a special pair of sex chromosomes which is found in bees and based fundamentally in whether or not the gamete is fertilized?
Haplodiploid System.
Females, queen and worker bees, are produced from fertilized eggs and are diploid.
The Males, or drones, are produced from an unfertilized egg and are haploid. (one less gamete, the sperm)
What mechanism of sex determination is control by environmental factors such as temperature?
Environmental Sex Determination
Some reptiles and fish have their sex determined by temperature.
For example, in the American alligator (Alligator mississippiensis), temperature controls sex development. When eggs of this alligator are incubated at 33°C, nearly all of them produce male individuals. When the eggs are incubated at a temperature significantly below 33°C, they produce nearly all females, whereas increasing percentages of females are produced above 34°C.
[Information on Sex Determination in Plants]
Most species of flowering plants, including pea plants, have a single type of diploid plant, or sporophyte, that makes both male and female gametophytes. However, the sporophytes of some species have two sexually distinct types of individuals, one with flowers that produce male gametophytes, and the other with flowers that produce female gametophytes.
Examples include hollies, willows, poplars, and date palms. Sex chromosomes, designated X and Y, are responsible for sex determination in many such species. The male plant is XY, whereas the female plant is XX. However, in some plant species with separate sexes, microscopic examination of the chromosomes does not reveal distinct types of sex chromosomes.
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What are the size differences in the X and Y chromosomes?
X is rather large carrying over 1,000 genes while the Y chromosome is quite small and carries less than 100 genes.
What are genes found on the X chromosome and not the Y chromosome?
What about genes found on the Y chromosome?
X-linked genes
Y-linked genes. Much less common considering the size.
What is another name for genes found on one sex chromosome and not the other? Typically is not used since most are found on the X chromosome.
Sex-linked genes
Why can a male not be homozygous or heterozygous for an x-linked gene?
The terms only apply to genes that are present in two copies. Males are XY hence no copy of the same gene in sex chromosomes for X-linked genes.
What is the term that describes having only one copy of a particular gene?
Hemizygous
A male mammal is hemizygous for an X-linked gene.
T/F Many recessive x-linked alleles cause disease in humans, and these diseases occur more frequenlty in women.
False. X-linked refers to diseases more common in men.
What is an example of an x-linked recessive disorder?
Hemophilia.
In individuals with hemophilia, blood does not clot properly, and a minor cut may bleed for a long time. Common accidental injuries that are minor in most people pose a threat of severe internal or external bleeding for hemophiliacs.
Hemophilia A is caused by a recessive X-linked allele that encodes a defective form of a clotting protein. If a mother is a heterozygous carrier of hemophilia A, each of her children has a 50% chance of inheriting the recessive allele. The following Punnett square shows a cross between an unaffected father and a heterozygous mother. XH designates an X chromosome carrying the dominant functional allele, and Xh-A is the X chromosome that carries the recessive nonfunctional allele for hemophilia A.
Although each child has a 50% chance of inheriting the hemophilia allele from the mother, only 1/2 of the sons will exhibit the disorder. Because a son inherits only one X chromosome, a son who inherits the recessive (disease-causing) allele from his mother will have hemophilia. However, a daughter inherits an X chromosome from both her mother and her father. In this example, a daughter who inherits the recessive allele from her mother also inherits a dominant allele from her father. This daughter will not have hemophilia, but if she passes the recessive allele to a son, he will have hemophilia.
[17.5 Variations in Inheritance Patterns and Their Molecular Basis]
What is the inheritance patterns of genes that segragate and assort independently?
Mendelian inheritance
In the first section of this chapter, we considered the inheritance pattern of traits affected by a single gene that is found in two variants, one of which is dominant over the other. This pattern is called simple Mendelian inheritance, because the phenotype ratios in the offspring clearly demonstrate Mendel’s laws.
T/F There are cases where the inheritance patterns of genes that segregate and assort independently do not display a simple dominant/recessive relationship.
True.
The transmission of these genes from parents to offspring does not usually produce the ratios of phenotypes we would expect on the basis of Mendel’s observations.
What is a prevalent allele in a population?
A wild-type allele. In most cases, a wild-type allele encodes a protein that is made in the proper amount and functions properly.
What is an allele that has been altered by mutation?
Mutant allele.
These tend to be rare in natural populations. In the case of Mendel’s seven characters in pea plants, the recessive alleles are due to rare mutations.
What do you call mutations that produce recessive alleles that are likely to decrease or eliminate the synthesis or functional activity of a protein?
These are called loss-of-function alleles.
To understand why many loss-of-function alleles are recessive, we need to take a quantitative look at protein function.
Use an example of a pea plant and its color of its flowers to explain the dominant phenotype of a heterozygote.
The gene encodes an enzyme (protein P) that is needed to convert a colorless molecule into a purple pigment. The P allele is dominant because one P allele encodes enough of the functional protein—50% of the amount found in a PP homozygote—to provide a purple phenotype. Therefore, the PP homozygote and the Pp heterozygote both make enough of the purple pigment to yield purple flowers. The pp homozygote cannot make any of the functional protein required for pigment synthesis, so its flowers are white.
If an organism like a homozygote has two dominant alleles, and is making 100% of its protein to exhibit the respective phenotype, how does an organism that is a heterozygote with only one dominant allele exhibit the phenotype with 50% production of proteins?
In other cases, however, an allele may be dominant because the heterozygote actually produces more than 50% of the functional protein. This increased production is due to the phenomenon of gene regulation. The dominant allele is up-regulated in the heterozygote to compensate for the lack of function of the recessive allele.
What is the phenomenon in which a mutation in a single gene can have multiple effects on an individual’s phenotype?
Pleiotropy
Pleiotropy occurs for several reasons, including the following:
The expression of a single gene can affect cell function in more than one way. For example, a defect in a microtubule protein may affect cell division and cell movement. A gene may be expressed in different cell types in a multicellular organism. A gene may be expressed at different stages of development.
Explain more about pleiotrophy and how the expression of one gene can affect more of the body.
In this genetics unit, we tend to discuss genes as they affect a single trait. This educational approach allows us to appreciate how genes function and how they are transmitted from parents to offspring. However, in all or nearly all cases, the expression of a gene is pleiotropic with regard to the characteristics of an organism. The expression of any given gene influences the expression of many other genes in the genome, and vice versa. Pleiotropy is revealed when researchers study the effects of gene mutations.
As an example of a pleiotropic effect, let’s consider cystic fibrosis (CF), which we discussed earlier as an example of a recessive human disorderIn the late 1980s, the gene for CF was identified. The gene encodes a protein called the cystic fibrosis transmembrane regulator (CFTR), which regulates ion balance by allowing the transport of chloride ions (Cl–) across cell membranes. The mutation that causes CF diminishes the function of this Cl– transporter, affecting several parts of the body in different ways. Because the movement of Cl– affects water transport across membranes, the most severe symptom of CF is the production of thick mucus in the lungs, which occurs because of a water imbalance. Similarly, thick mucus can also block the tubes that carry digestive enzymes from the pancreas to the small intestine. Without these enzymes, certain nutrients are not properly absorbed into the body. As a result, persons with CF may show poor weight gain.
Another effect is seen in the sweat glands. The Cl– transporter has the function of recycling salt out of the glands and back into the skin before it can be lost to the outside world. Persons with CF have excessively salty sweat due to their inability to recycle salt back into their skin cells. A common test for CF is the measurement of salt on the skin. Taken together, we can see that a defect in CFTR has multiple effects throughout the body.
What is the phenomenon in which a heterozygote that carries two different alleles exhibits a phenotype that is intermediate between the phenotypes of the corresponding homozygous individuals?
Incomplete dominance
Who discovered incomplete dominance in 1905 by observing this pattern of inheritance of alleles affecting flower color in the four-o’ clock plant?
Carl Correns
Shows a cross between two four-o’clock plants: a red-flowered homozygote and a white-flowered homozygote. The allele for red flower color is designated CR, and the white allele is CW. These alleles are designated with superscripts rather than upper- and lowercase letters because neither allele is dominant. The offspring of this cross have pink flowers—they are CRCW heterozygotes with an intermediate phenotype.
What would the Punnett square look like in incomplete dominance for the four o’ clock plant?
4 squares all labeled with alleles with subscripts since none of them are dominate.
The cases where the resulting offspring have both red and white combinations would be pink. Same alleles in the other two offspring would be completely red or white.
What is the phenomenon in which a gene has three or more alleles in a natural population?
Multiple alleles
Particular phenotypes depend on which two alleles each individual inherits. ABO blood types in humans are an example of phenotypes produced by multiple alleles.
What are antigens (in the case of red blood cells)?
They are substances that may be recognized as foreign material when introduced into the body of an animal.
What are the two types of surface antigens that can be found on red blood cells?
A and B antigens
How is the synthesis of these antigens determined?
By enzymes that are encoded by a gene that exists in three alleles, designated I^A, I^B, and i.
What is the i allele recessive to?
I^A and I^B.
What type of alleles does someone have if they are blood type O?
Explain the other blood types.
They are ii homozygous and do not produce surface antigen A or B.
The red blood cells of an IAIA homozygous or IAi heterozygous individual have surface antigen A (blood type A). Similarly, a homozygous IBIB or heterozygous IBi individual produces surface antigen B (blood type B). A person who is IAIB heterozygous makes both antigens, A and B, on every red blood cell (blood type AB). The phenomenon in which a single individual expresses two alleles is called codominance.
What is the phenomenon in which a single individual expresses two alleles? Think AB blood type.
Codominance
What is the molecular explanation for codominance?
Biochemists have analyzed the carbohydrate tree produced in people of differing blood types. The differences are shown schematically. In type O, the carbohydrate tree is smaller than in type A or type B because a sugar has not been attached to a specific site on the tree. People with blood type O have a loss-of-function mutation in the gene that encodes the enzyme that attaches a sugar at this site. This enzyme, called a glycosyl transferase, is inactive in type O individuals. In contrast, the type A and type B antigens have sugars attached to this site, but each of them has a different sugar.
This difference occurs because the enzymes encoded by the IA allele and the IB allele have slightly different active sites. As a result, the enzyme encoded by the IA allele attaches a sugar called N-acetylgalactosamine to the carbohydrate tree, whereas the enzyme encoded by the IB allele attaches galactose. N-Acetylgalactosamine is represented by an orange hexagon in Table 17.2, and galactose by a green triangle.
What is the phenotype range that individuals with a particular genotype exhibit under differing environmental conditions?
Norm of reaction
Could you study the norm of reaction in a wild population of squirrels?
No. You need a genetically homogenous population to study the norm of reaction. A wild population of squirrels is not genetically homogenous, so it could not be used.
[17.6 Gene Interaction]
What was pivotabl in establishing the science of genetics and what did it help?
The study of single genes.
This focus allowed Mendel to formulate the basic laws of inheritance for traits with a simple dominant/recessive inheritance pattern.
Likewise, this approach helped later researchers understand inheritance patterns involving incomplete dominance and codominance, as well as traits that are influenced by an individual’s sex.
Are all or nearly all traits influenced by many genes?
Yes.
For example, in both plants and animals, height is affected by genes that encode proteins involved in the production of growth hormones, cell division, the uptake of nutrients, metabolism, and many other functions. Variation in any of the genes involved in these processes is likely to influence an individual’s height.
If height is controlled by many genes, how was Mendel able to study the effects of a single gene that produced tall or dwarf pea plants?
The answer lies in the genotypes of his strains. Although many genes affect the height of pea plants, Mendel chose true-breeding strains that differed with regard to only one of those genes.
[Information of hypothetical example of genes affecting height in pea plants]
As a hypothetical example, let’s suppose that pea plants have 10 genes affecting height, which we will call K, L, M, N, O, P, Q, R, S, and T. The genotypes of two hypothetical strains of pea plants may be:
Tall strain:
KK LL MM NN OO PP QQ RR SS TT
Dwarf strain:
KK LL MM NN OO PP QQ RR SS tt
In this example, the tall and dwarf strains differ at only a single gene. One strain is TT and the other is tt, and this accounts for the difference in their height. If we make crosses of tall and dwarf plants, the genotypes of the F2 offspring will differ with regard to only one gene; the other nine genes will be identical in all of them. This approach allows a researcher to study the effects of a single gene even though many genes may affect a single character.
None
What is the phenomenon in which a single trait is controlled by two or more genes, each of which has two or more alleles?
Gene interaction
What is a gene interaction in which the alleles of one gene mask the expression of the alleles of another gene?
Epistasis
What was the study that helped show unexpected gene interation in regards to epistasis?
An example is the unexpected gene interaction discovered by English geneticists William Bateson and Reginald Punnett in the early 1900s, when they were studying crosses involving the sweet pea, Lathyrus odoratus. A cross between a true-breeding purple-flowered plant and a true-breeding white-flowered plant produced an F1 generation with all purple-flowered plants and an F2 generation with a 3:1 ratio of purple- to white-flowered plants. Mendel’s laws predicted this result.
The surprise came when the researchers crossed two different true-breeding varieties of white-flowered sweet peas.
All of the F1 generation plants had purple flowers! When these plants were allowed to self-fertilize, the F2 generation had purple-flowered and white-flowered plants in a 9:7 ratio. From these results, Bateson and Punnett deduced that two different genes were involved.
To have purple flowers, a plant must have one or two dominant alleles for each of these genes. The relationships among the alleles are as follows:
C (one allele for purple) is dominant to c (white) P (an allele of a different gene for purple) is dominant to p (white) cc masks P, or pp masks C, resulting in white flowers in either case
How do we explain these results at the molecular and cellular level for epistasis?
Epistatic interactions often arise because two or more different proteins are involved in a single cellular function. For example, two or more proteins may be part of a metabolic pathway leading to the formation of a single product. This is the case for the formation of a purple pigment in the sweet pea strains we have been discussing:
In this example, a colorless precursor molecule must be acted on by two different enzymes to produce the purple pigment. Gene C encodes a functional protein called enzyme C, which converts the colorless precursor into a colorless intermediate. The recessive c allele results in a lack of production of enzyme C in the cc homozygote. Gene P encodes the functional enzyme P, which converts the colorless intermediate into the purple pigment. Like the c allele, the p allele results in an inability to produce a functional enzyme. A plant homozygous for either of the recessive alleles does not make any functional enzyme C or enzyme P. When either of these enzymes is missing, the plant cannot make the purple pigment and has white flowers. Note that the results observed in Figure 17.19 do not conflict with Mendel’s laws of segregation or independent assortment. Mendel investigated the effects of only a single gene on a given character. The 9:7 ratio is due to a gene interaction in which two genes affect a single character.
What is a trait with clearly defined phenotypic variants?
Discrete trait.
This was discussed in the examples of red and white eyes in fruit flies and round or wrinkled seeds in garden peas. These phenotypes do not overlap.
What is a trait that shows continous variation over a range of phenotypes?
Quantitative traits.
In humans, quantitative traits include height, weight, skin color, metabolic rate, and heart size. In the case of domestic animals and plant crops, many of the traits that people consider desirable are quantitative in nature, such as the number of eggs a chicken lays, the amount of milk a cow produces, and the number of apples on an apple tree. Consequently, much of our modern understanding of quantitative traits comes from agricultural research.
What refers to a trait for which several or many genes contribute to the outcome?
Polygenic
For many polygenic traits, genes contribute to the phenotype in an additive way. Also, environmental factors often have a major effect on quantitative traits. For example, an animal’s diet affects its weight, and the amounts of rain and sunlight that fall on an apple tree affect how many apples it produces.
[17.7 Genetics and Probability]
How is Mendel’s laws of inheritance useful in predicting the outcomes of genetic crosses?
For many polygenic traits, genes contribute to the phenotype in an additive way.
Also, environmental factors often have a major effect on quantitative traits. For example, an animal’s diet affects its weight, and the amounts of rain and sunlight that fall on an apple tree affect how many apples it produces.
What is the chance that an event will have a particular outcome?
Probability
What does the probability of a given outcome depend on?
The number of possible outcomes.
For example, if you draw a card at random from a 52-card deck, the probability that you will get the jack of diamonds is 1 in 52, because 52 outcomes are possible. In contrast, only two outcomes are possible when you flip a coin, so the probability is one in two (1/2, or 0.5, or 50%) that the heads side will be showing when the coin lands.
What is the general formula for the probability (P) that an event will have a specific outcome?
P = number of times an event occurs
divided by
Total of number of possible outcomes
Since tossing a coin has a 50% chance to land on heads or tails, why might there be a chance that if we toss the coin 6 times, that only 25% of the time might be tails?
Because these events are independent of each other.
What is the deviation between the observed and expected outcomes due to random chance?
Random sampling error
What is the probability that two or more independent events will occur is equal to the product of their individual probabilities?
Product rule.
As we have already discussed, events are independent if the outcome of one event does not affect the outcome of another.
The acquisition of traits by their transmission from parent to offspring is called _________
inheritance or heredity
Most of Mendel’s experiments were conducted using _______ plants.
pea, garden pea, peas, Pisum, or Pisum sativum
Multiple Choice Question
Mendel’s work involved quantitative experiments and careful analysis of the ______ of offspring carrying specific traits.
Multiple choice question.
type
number
sex
number
A single-factor cross is one in which an experimenter follows ______.
Multiple choice question.
only one genus of plants
the characters of only one variant
the variants of only one character
only one allele of a gene pair
the variants of only one character
When two true-breeding plants that differ in a single character are crossed, the _______ monohybrids display the trait, and the ___________ trait is masked.
Blank 1: dominant
Blank 2: recessive
True or false: Inheritance is the acquisition of traits by their transmission from offspring to parent.
True false question.
True
False
False
Mendel’s “unit factors” are now called ________ and their variant forms are referred to as __________
Genes; Alleles
Mendel’s proposed his laws of inheritance based on ______.
Multiple choice question.
his knowledge of the structure of DNA
quantitative experiments
observation of chromosomes under the microscope
quantitative experiments
In pea plants, when a true-breeding line with axial flowers is crossed with a true-breeding line with terminal flowers, all of the F1 offspring have axial flowers. What phenotypic ratio is expected in the F2 generation?
Multiple choice question.
All terminal
1 axial: 3 terminal
3 axial: 1 terminal
1 axial:1 terminal
All axial
3 axial: 1 terminal
A cross in which only one character is studied is called a(n) _____-______ cross.
single factor
In pea plants, the allele T codes for tall plants and the allele t codes for short plants. If a plant is short, this would be considered its ______.
Multiple choice question.
genome
phenotype
proteome
genotype
phenotype
In pea plants, purple flowers are dominant to white flowers, and the purple and white alleles are represented with P and p, respectively. In a cross between two heterozygotes, what proportion of the offspring are expected to be purple?
Multiple choice question.
All of the offspring
None of the offspring
1/2
1/4
3/4
3/4
An individual who is homozygous for a given gene carries ______ of the gene.
Multiple choice question.
two recessive alleles
two different alleles
two identical alleles
two dominant alleles
two identical alleles
A single-factor cross is one in which an experimenter follows ______.
Multiple choice question.
only one allele of a gene pair
only one genus of plants
the variants of only one character
the characters of only one variant
the variants of only one character
The combination of alleles that an individual possesses, such as Tt or TT, is the individual’s _________.
Genotype
An individual who carries two different alleles of a gene is said to be _________ with respect to that gene.
heterozygous
A diagram that can be used to predict the outcome of a simple genetic cross is called a(n) ___________ square.
Punnett
An individual with a dominant phenotype may be either homozygous or heterozygous. To determine the exact genotype of this individual a method called a(n) _______ can be used.
testcross
In pea plants, green pods are dominant to yellow pods. The genotype of a plant with green pods must be ______.
Multiple choice question.
homozygous dominant
either homozygous recessive or heterozygous
either homozygous dominant or heterozygous
heterozygous
homozygous recessive
either homozygous dominant or heterozygous
In a Punnett square, the symbols that make up the headings for the columns and rows correspond to the ______.
Multiple choice question.
genotypes of the parents
male and female gametes
phenotypes of the offspring
male and female gametes
An individual who is homozygous for a given gene carries ______ of the gene.
Multiple choice question.
two recessive alleles
two dominant alleles
two different alleles
two identical alleles
two identical alleles
In pea plants, tall is dominant to short. When a tall plant of unknown genotype is testcrossed with a short plant, half of the offspring are tall, and half are short. What was the genotype of the tall parent?
Multiple choice question.
Heterozygous
Homozygous for the recessive allele
Homozygous for the dominant allele
Heterozygous
A Punnett square for a single trait should be set up as a ______ square (Not counting the squares for parental gametes).
Multiple choice question.
2 x 4
3 x 3
4 x 4
2 x 2
2 x 2
What is the purpose of a testcross?
Multiple choice question.
To determine the genotype of an individual with a dominant phenotype
To determine which trait is dominant and which is recessive
To determine how many genes affect a trait
To determine the genotype of an individual with a dominant phenotype
In a two-factor cross, genes that are close together on a chromosome do not follow Mendel’s law of _________ __________
Independent assortment
An individual with a dominant phenotype, may have a genotype of
Multiple select question.
homozygous recessive
homozygous dominant
heterozygous
homozygous dominant
heterozygous
What aspect of chromosome behavior during meiosis explains Mendel’s law of segregation?
Multiple choice question.
Separation of homologous chromosomes during meiosis I
Crossing over during meiosis I
Compaction of chromatin into chromosomes
Replication of a chromosome to form two sister chromatids
Separation of homologous chromosomes during meiosis I
The results of a testcross indicate that all of the offspring have a dominant phenotype. The genotype of the parent in question must be ______.
Multiple choice question.
homozygous dominant
homozygous recessive
heterozygous
homozygous dominant
After DNA replication in a heterozygote, the two sister chromatids on a single chromosome contain ______.
identical alleles
different alleles
new alleles
A two-factor cross is one in which an experimenter follows the inheritance of ______.
Multiple choice question.
two different populations
two different characters
two variants of a single character
two sets of chromosomes
two different characters
Independent assortment of alleles of different genes can be explained by the random alignment of __________ _________ of chromosomes during meiosis I.
Blank 1: homologous
Blank 2: pairs or pair
True or false: In a two-factor cross, genes that are close together on the same chromosome follow Mendel’s law of independent assortment.
Multiple choice question.
False
True
False
Carriers of the cystic fibrosis allele are phenotypically ______.
Multiple choice question.
abnormal
recessive
normal
normal
If the offspring of a cross show an intermediate phenotype in the heterozygote, the pattern of inheritance is that of _________ dominance
incomplete
The phenotypic range exhibited by individuals with a particular genotype under differing environmental conditions is called the __________ of ________
norm, reaction
In pea plants, yellow peas (Y) are dominant to green (y) and round peas (R) are dominant to wrinkled (r). Two pea plants were crossed, one with yellow round peas and one with green wrinkled peas. What were the genotypes of the parents?
Question 1 options:
The yellow round was YYRR and the green wrinkled was yyrr
The yellow round was YyRr and the green wrinkled was YyRr
The yellow round was yyrr and the green wrinkled was YYRR
The yellow round was YYrr and the green wrinkled was yyRR
The yellow round was YYRR and the green wrinkled was yyrr
Some plants have flower color that is determined by incomplete dominance, thus both genes are expressed and the color is a blend of the two. In the Four O’clock flower heterozygotes have pink flowers while homozygotes are red or white. A plant with pink flowers was crossed with a plant with red flowers. If 300 offspring were produced, what number of the F1 Generation would have red flowers?
0
75
150
300
150
In one family there is a skin tone that seems to “skip” a generation. For example the grandmother has it, her daughter does not, but her granddaughter does. What is the most likely explanation for this?
Question 3 options:
This skin tone is not heritable
This skin tone is a recessive trait
This skin tone is a dominant trait
This skin tone is caused by a mutation
This skin tone is a recessive trait
Tay Sachs is an autosomal recessive condition that is caused by a mutation in the gene that encodes for the hexA enzyme. This enzyme normally degrades a specific type of lipid in brain cells. When this lipid is not degraded, it results in degradation of brain neurons. Two individuals who do NOT have Tay Sachs have a child that does. What is the most likely explanation for this?
Question 4 options:
There was a spontaneous mutation in both of the child’s chromosomes for hexA
The parents were carriers of the condition
There was a spontaneous mutation in one of the child’s chromosomes for hexA
The mother was not a carrier of the condition but the father was
Both A and D are likely explanations
The parents were carriers of the condition
Some plants have flower color that is determined by incomplete dominance, thus both genes are expressed and the color is a blend of the two. In the Four O’clock flower heterozygotes have pink flowers while homozygotes are red or white. A plant with pink flowers was crossed with a plant with red flowers. If 300 offspring were produced, what number of the F1 Generation would have white flowers?
Question 5 options:
0
75
150
300
150 WRONG
The drug Plavix requires the enzyme CYP2C19 to take it from the prodrug form to the drug form (enzyme A below) and it requires the enzyme CES1 to convert it from active to inactive (enzyme 1 below). The active form of the drug is effective in preventing blood clots but is toxic in higher doses. Individuals with a mutation in this CES1 gene produce a version of CES1 that is not functional. You are a physician trying to determine the dosage of Plavix for a patient who is homozygous for the mutated version of the gene. What should you do?
ProDrug > Drug > Inactive Drug and enzymes
Question 6 options:
Decrease the normal dosage because they are making too much of the drug
Increase the normal dosage because they are making too much of the toxic endproduct
Increase the normal dosage because they are not making enough of the toxic endproduct
Choose another drug as the individual will likely suffer from too much toxicity
Choose another drug as the individual will likely suffer from too much toxicity
The drug Plavix requires the enzyme CYP2C19 to take it from the prodrug form to the drug form (enzyme A below) and it requires the enzyme CES1 to convert it from active to inactive (enzyme 1 below). The active form of the drug is effective in preventing blood clots but is toxic in higher doses. Individuals with a mutation in this CES1 gene produce a version of CES1 that is not functional. You are a physician trying to determine the dosage of Plavix for a patient whose father is homozygous for the mutated version of the CES1 gene and whose mother is heterozygous for the mutation version of the CES1 gene. The mutation is a recessive condition. What does this mean for you and the patient?
ProDrug > Drug > Inactive Drug and enzymes
Question 7 options:
There is a 25% chance that you will need to increase the dosage of the drug
There is a 25% chance that you will need to decrease the dosage of the drug
There is a 50% chance that you will need to increase the dosage of the drug
There is a 50% chance that you will need to decrease the dosage of the drug
There is a 25% chance that you will need to decrease the dosage of the drug WRONG
The drug Plavix requires the enzyme CYP2C19 to take it from the prodrug form to the drug form (enzyme A below) and it requires the enzyme CES1 to convert it from active to inactive (enzyme 1 below). The active form of the drug is effective in preventing blood clots but is toxic in higher doses. Individuals with a mutation in the CYP2C19 gene produce a version of CYP2C19 that is 50%less effective. You are a physician trying to determine the dosage of Plavix for a patient who is homozygous for the mutated version of the CYP2C19 gene. What should you do?
ProDrug > Drug > Inactive Drug and enzymes
Question 8 options:
Decrease the normal dosage because they are making too much of the toxic endproduct
Increase the normal dosage because they are making too much of the toxic endproduct
Increase the normal dosage because they are not making enough of the drug
Decrease the normal dosage because they are making too much of the drug
Increase the normal dosage because they are not making enough of the drug
Cystic fibrosis is the most common lethal genetic disease among Caucasians. with cystic fibrosis produce a mutated chloride (Cl-) channel protein that results in abnormal ion and water transport across epithelia such as that lining the lung, often making it difficult to breathe. Cystic fibrosis is inherited in an autosomal recessive manner; individuals who are heterozygous for the cystic fibrosis allele are carriers but do not exhibit the disease. An individual who has the disease has children with an individual who is a carrier. What is the chance that their child will not have the disease?
Question 9 options:
0%
25%
50%
75%
100%
75% WRONG
In pea plants, yellow peas (Y) are dominant to green (y) and round peas (R) are dominant to wrinkled (r). Two pea plants were crossed, one homozygous dominant for yellow round peas and one homozygous recessive for green wrinkled peas. What was the phenotypic ratio of the F2 generation?
Question 10 options:
9 yellow round: 3 yellow wrinkled: 3 green round 1: green wrinkled
9 yellow wrinkled: 3 yellow round: 3 green round: 1 green wrinkled
9 green wrinkled: 3 green round: 3 yellow wrinkled: 1 yellow round
9 green round: 3 green wrinkled: 3 yellow round: 1 yellow wrinkled
9 yellow round: 3 yellow wrinkled: 3 green round 1: green wrinkled
Cystic fibrosis is the most common lethal genetic disease among Caucasians. with cystic fibrosis produce a mutated chloride (Cl-) channel protein that results in abnormal ion and water transport across epithelia such as that lining the lung, often making it difficult to breathe. Cystic fibrosis is inherited in an autosomal recessive manner; individuals who are heterozygous for the cystic fibrosis allele are carriers but do not exhibit the disease. An individual who has the disease has children with an individual who does not have the disease and is not a carrier. What is the chance that their child will have the disease?
Question 11 options:
0%
25%
50%
75%
100%
25% WRONG
In humans, long eyelashes (L) are dominant to short eyelashes (l). If an individual is Ll for eyelash length, what does this mean?
Question 12 options:
The individual will have long eyelashes
All offspring will have long eyelashes when crossed with the Ll genotype
All offspring will have long eyelashes when crossed with the ll genotype
The individual is homozygous dominant for eyelashes
All of the above are true
The individual will have long eyelashes
The Law of Independent Assortment means that
Question 13 options:
A gamete will have both members of a homologous pair
A gamete will have only one member of a homologous pair
Alleles for different traits are linked (ex. If you have red hair, you must also have blue eyes)
Alleles for different traits do not have to be inherited together (ex. Red hair and blue eyes are not linked
Alleles for different traits do not have to be inherited together (ex. Red hair and blue eyes are not linked
An individual has green eyes and is homozygous recessive. What is her phenotype?
Question 14 options:
Green eyes
gg
GG
Gg
gg WRONG
Cystic fibrosis is the most common lethal genetic disease among Caucasians. with cystic fibrosis produce a mutated chloride (Cl-) channel protein that results in abnormal ion and water transport across epithelia such as that lining the lung, often making it difficult to breathe. Cystic fibrosis is inherited in an autosomal recessive manner; individuals who are heterozygous for the cystic fibrosis allele are carriers but do not exhibit the disease. An individual who has the disease has children with an individual who does not have the disease and is not a carrier. What is the chance that their child will not have the disease?
Question 15 options:
0%
25%
50%
75%
100%
0% WRONG
