Chapter Four Flashcards
What is Mendelian Inheritance pattern?
The common pattern of inheritance observed by Mendel, which involves the transmission of eukaryotic genes that are located on the chromosomes found within the cell nucleus.
What are the two laws the traits of Mendelian inheritance follow?
The law of segregation
The law of independent assortment.
What is simple mendelian inheritance?
An inheritance pattern involving a simple, dominant/recessive relationship that produces observed ratios in the offspring that readily obey Mendel’s laws.
What is incomplete dominance?
Inheritance pattern that occurs when the heterozygote has a phenotype that is intermediate between either corresponding homozygote.
Ex: cross between red and white flower produces a pink flower.
What is overdominance?
Inheritance pattern occurs when the heterozygote has a trait that is more beneficial than either homozygote.
What is codominance?
Inheritance pattern occurs when the heterozygote expresses both alleles simultaneously without forming an intermediate phenotype.
Ex: parents with A blood type and B blood type will produce an offspring with AB blood type
What is sex-influenced inheritance?
Inheritance pattern the refers to the effect of sex on the phenotype of the individual. Some alleles are recessive in one sex and dominant in the opposite sex.
What is sex-limited inheritance?
Inheritance pattern that refers to traits that occur in only one of the two sexes.
What are lethal alleles?
An allele that has the potential of causing the death of an organism.
Which of the following statements is true?
a. Not all inhertance patterns follow a strict dominant/recessive relationship.
b. Geneticists want to understand both inhertiance patterns and the underlying molecular mechanism that cause them to happen.
c. Different inheritance patterns are explained by a variety of different molecular mechanisms
d. all of the above.
d. all of the above.
What are wild-type alleles?
An allele that is fairly prevalent in a natural population, generally greater than 1% of the population. For polymorphic genes, there may be more than one wild-type allele.
What is genetic polymorphism?
When two or more alleles occur in population; each allele is found at a frequency of 1% or higher.
What are mutant alleles?
Alleles that have been created by altering a wild-type allele by mutation.
Does a PP individual produce more of the protein encoded by the P gene than is necessary for the purple flower?
Yes. The PP homozygote probably makes twice as much of the protein that is needed for purple pigment formation.
What are thre three explanations that account for most dominant mutant alleles?
A gain-of-function mutation
A dominant-negative mutation,
Haplo-insufficiency.
What is gain-of-function mutation?
A mutation that causes a gene to be expressed in an additional place where it is not normally expressed or during a stage of development when it is not normally expressed.
What is dominant-negative mutation?
A mutation that produces an altered gene product that acts antagonistically to the normal gene product. Shows a dominant pattern of inheritance.
What is haploinsufficiency?
The phenomenon in which a person has only a single functional copy of a gene, and that single functional copy does not produce a normal phenotype.
What is incomplete penetrance?
A pattern of inheritance in which a dominant allele does not always control the phenotype of the individual.
What is expressivity?
The degree to which a trait is expressed.
For example, flowers with deep red color have a high expressivity of the red allele.
Which of the following is not an example of a wild-type allele?
a. yellow-flowered elderflower orchid
b. Red-flowered elderflower orchid
c. a gray elephant
d. an albino elephant.
d. an albino elephant.
Dominant alleles may results from mutations that cause
a. the overexpression of a gene or its protein product.
b. a protein to inhibit the function of a normal protein
c. a protein to be inactive and 50% of the normal protein is insufficient for a normal phenotype
d. all of the above.
d. all of the above.
Polydactyly is a condition in which a person has extra fingers and/or toes. It is caused by a dominant allele. If a person carries this allel but does not have any extra fingers or toes, this is an example of
a. haploinsufficiency.
b. a dominant negative mutation
c. incomplete penetrance
d. a gain-of-function mutation.
c. incomplete penetrance
What is temperature sensative allele?
An allele in which the resulting phenotype depends on the environment temperature.
What are the two main factors that determines an organisms traits?
Genes and the environment.
What is norm of reaction?
The effects of environmental variation on an individual’s traits.
How do researchers evaluate norm of reaction?
Begin with true-breeding strains that have the same genotype and subject them to different environmental conditions.
The outcome of an individual’s traits is controlled by what?
a. genes
b. the environment
c. genes and the environment
d. neither genes nor the environment
c. genes and the environment
At the moleular level, what is the explanation for why the flowers are pink instead of red?
50% of the functional enzymes is not enough to give a red color.
At which level is incomplete dominance more likely to be observed– at the molecular/cellular level or at the organism level?
Molecular/cellular level.
What is heterozygote advantage?
Or overdominance.
An inheritance pattern in which a heterozygote is more vigorous than either of the corresponding homozygotes.
Why does heterozygote have an advantage for sickle cell anemia?
The heterozygote is resistant to malaria.
Overdominance is usually due to what?
Two alleles that produce proteins with slightly different amino acid sequences.
What’s a second way to expalin overdominance?
In some cases, a protein functions as a complex of multiple subunits; each subunit is composed of one polypeptide.
What is a third way to explain overdominance?
The proteins encoded by each allele exhibit differences in their functional activity.
Most genes exist in what?
Multiple alleles, when the same genes exists in two or more alleles. within a population
Which allele is an example of loss-of-function allele in blood type?
The i allele is a loss-of-function allele
What is codominance again?
A pattern of inheritance in which two alleles are both expressed in the heterozygous condition.
A pink-flowered four-o’clock is crossed to a red-flowered plant. What is the expected outcome for the offspring?
a. all pink
b. all red
c. 1 red: 2 pink: 1 white
d. 1 red: 1 pink
d. 1 red: 1 pink
A person with type AB blood has a child with a person with type O blood. What are the possible blood types of the child?
a. A and B
b. A, B, and O
c. A, B, AB, and O
d. O only.
a. A and B
What is X-linked recessive?
An allele or trait in which the gene is found on the x chromosome and the allele is recessive relative to a corresponding dominant allele.
What is a reciprocal cross?
A pair of crosses in which the traits of the two parents differ with regard to sex. For example, one cross could be a red-eyed female fly and a white-eyed male fly, and the reciprocal cross would be a red-eyed male fly and a white-eyed female fly.
What is hemizygous?
The single copy of an x-linked gene in the male. A male mammal is said to be hemizygous for x-linked genes.
What are holandric genes?
A gene on the Y chromosome
What is pseudoautosomal inheritance?
The inheritance pattern of genes taht are found on both the X and Y chromosomes. Even though such genes are located physically on the sex chromosomes, their pattern of inheritance is identical to that of autosomal genes.
Why are the homologous regions of the X and Y chromosomes important during meiosis?
They are important for chromosome synapsis during meiosis
A cross is made between a white-eyed female fruit fly and a red-eyed male. What would be the reciprocal cross?
a. female is XwXw and male is XwY
b. Female is Xw+Xw+ and male is Xw+Y
c. Female is Xw+Xw+ and male is XwY
d. Female is XwXw and male is Xw+Y
c. Female is Xw+Xw+ and male is XwY
Hemophilia is a blood clotting disorder in humans that follows an X-linked recessive pattern of inheritance. A man with hemophilia and woman without hemophilia have a daughter with hemophilia. If you let H represent the normal allele and h the hemophilia allele, what are the genotypes of the parents?
a. mother is XHXh and father is XhY
b. Mother is XhXh and father is XhY
c. mother is XhXh and father is XHY
d. mother is XHXh and father is XHY
a. mother is XHXh and father is XhY
What is the difference between Sex-linked inheritance and sex-influenced inheritance?
Sex-influenced genes are autosomal, not on the X or Y chromosomes.
What is sex-limited inheritance again?
An inheritance pattern in which a trait is found in only one of the two sexes.
What is sexual dimorphism?
Species in which the males and females are morphologically distinct.
What is the molecular explanation for sex-limited inheritance?
Certain traits are expressed only in males or females, possible due to differences in the levels of sex hormones or other factors that differ between the sexes.
A female cow with scurs and a male bull with no scurs have an offspring. This offspring could be
a. a female with scurs or a male with scurs
b. a female with no scurs or a male with scurs
c. a female with scurs or a male with no scurs
d. a female with no scurs or a male with no scurs.
b. a female with no scurs or a male with scurs
What is an essential gene?
A gene that is essential for survival.
What are nonessential genes?
Genes that are not absolutely required for survival, although they are likely to be beneficial to the organism
Approximatley what fraction of genes are essential genes?
1/3
What are conditional lethal alleles?
Alleles that are lethal, but only under certain environmental conditions.
What are temperature-sensitive lethal alleles?
An allele that is lethal at a certain environmental temperature.
What are semilethal alleles?
Lethal alleles that kill some individuals but not all
Why do you think the heterzygote survies with developmental abnormalities, whereas the homozygote dies?
The heterozygote has one normal copy of the gene, which allows for development to proceed in a way that is not too far from normal. Having two mutatant copies of the gene probably messes up development to a degree that is incompativle with survival.
What is the age of onset?
For alleles that cause genetic diseases, the time of life at which disease symptoms appear.
The Manx phenotype in cats is caused by a dominant allele that is lethal in the homozygous state. A Manx cat is crossed to a normal cat. What is the expected outcome for the surviving offspring?
a. All Manx offspring
b. All normal offspring
c. 1 normal offspring, 1 Manx offspring
d. 1 normal offspring, 2 Manx offspring
c. 1 normal offspring, 1 Manx offspring
What is pleiotropy?
The multiple effects of a single gene on the phenotype of an organism
What are some of the reasons pleiotropy occurs?
- the expression of a single gene can affect cell function in more than one way.
- A gene may be expressed in different cell types in a multicellular organism
- A gene may be expressed at different stages of development
Which of the following is a possible explanation for pleiotropy?
a. the expression of a single gene can affect cell function in more than one way.
b. A gene may be expressed in different cell types in a multicellular organism
c. A gene may be expressed at different stages of development
d. all of the above
d. all of the above.
What is gene interaction?
When two or more different genes influence the outcome of a single trait.
What is epistasis?
An inheritance pattern in which the alleles of one gene mask the phenotypic effects of the alleles of a different gene
What is complementation?
A phenomenon in which two parents that express the same or similar recessive phenotypes produce offspring with a wild-type phenotype
What is gene modifier effects?
A phenomenon in which an allele of one gene modifies the phenotypic outcome of the alleles of a different gene.
What is Gene Redundancy?
A pattern in which the loss of function in a single gene has no phenotypic effect, but the loss of function of two genes has an effect. Functionality of only one of the two genes is necessary for a normal phenotype; the genes are functionally redundant.
What is recessive epistasis?
A form of epistasis in which an individual must be homozygous for either recessive allele to mask a particular phenotype.
What is gene knockout?
When both copies of a normal gene have been replaced by an inactive mutant gene.
What are paralogs?
Homologous genes within a single species that constitute a gene family.
At the molecular level (with regard to loss-of-function alleles), explain why the ttvv homozygote has an ovate capsule phenotype?
The tow genes are redundant. Having one normal copy of either gene produces a triangular capsule. If both genes are inactive, an ovate capsule is produced.
Two different strains of sweet peas are true-breeding and have white flowers. When these strains are crossed together, the F1 offspring all have purple flowers. This phenomenon is called
a. epistasis
b. complmentation
c. incomplete dominance
d. incomplete penetrance
b. complmentation
If the F1 offspring from question 1. are allowed to self-fertilize, what is the expected outcome fro the F2 offspring?
a. all white
b. all purple
c. 2 purple to 1 white
d. 9 purple to 7 white.
d. 9 purple to 7 white
Discuss the difference between sex-influenced, sex-limited, and sex-linked inheritance.
Sex-influenced traits are influenced by the sex of the individual even though the gene that governs the trait may be autosomally inheritated. Sex-limited traits are an extreme example of sex influence. The expression of a sex-limited trait is limited to one sex. Sex-linked traits involve traits whose genes are found on the sex chromosomes.
Let’s suppose a recessive allele encodes a completely defective protein. If the functional allele is dominant, what does that tell you about the amount of the functional protein that is sufficient to cause the phenotype? What if the allele shows incomplete dominance?
If the normal allele is dominant, it tells you that one copy of the gene produces a sufficient amount of the protein encoded by the gene. Having twice as much of this protein, as in the normal homozygote, does not alter the phenotype. If the allele is incompletely dominant, this means that one copy of the normal allele does not produce the same trait as the homozygote.
An allele in drosophila produces a star-eye trait in the heterozygous individual. However, the star-eye allele is lethal in homozygotes. What would be the ratio and phenotypes of surviving flies if star-eyed flies were crossed to each other?
1 normal: 2 star-eyed
The blood serum from one individual is known to agglutinate the red blood cells from a second individual. List the pairwise combinations of possible genotypes that individual 1 and 2 could be. If individual 1 is the parent of individual 2, what are his or her possible genotypes?
If individual 1 is ii, individual 2 could be IAIA, IAi, IBIB, or IAIB
If individual 1 is IAi or IAIA, individual 2 could be IBi, IBIB, or IAIB
If individual 1 is IBi or IBIB, individual 2 could be IAi, IAIA, or IAIB
Assuming individual 1 is the parent of individual 2:
If individual 1 is ii, individual 2 could be IAi or IBi
If individual 1 is IAi, individual 2 could be IBi or IAIB
If indibidual 1 is IAIA, individual 2 could be IAIB
If individual 1 is IBi, individual 2 could be IAi or IAIB
If individual 1 is IBIB, individual 2 could be IAIB
A woman with type B blood has a child with type O blood. What are the possible geneotypes and blood types of the father?
The father could be IAIB, IBIB, or IAIA. He is contributing the O allele to his offspring. Genotypically, he could be IAi, IBi, or ii and have type A, B, or O blood respectively
