Unit 4 (Week 14 Epigenetics, Linkage, and Extranuclear Inheritance) Flashcards
Mendelian inheritance patterns follow three general rules which are? (3)
- Except in the case of rare mutations, genes are passed unaltered from cell to cell, and from generation to generation.
- The genes obey Mendel’s law of segregation.
- For crosses involving two or more genes, the genes obey Mendel’s law of independent assortment.
Select all that apply
What are the three general rules for genes that follow a Mendelian pattern of inheritance?
Multiple select question.
The genes interact in an additive way to produce a phenotype.
For crosses involving two or more genes, the genes obey Mendel’s law of independent assortment.
The genes obey Mendel’s law of segregation.
Genes are generally passed unaltered from cell to cell, and from generation to generation.
For crosses involving two or more genes, the genes obey Mendel’s law of independent assortment.
The genes obey Mendel’s law of segregation.
Genes are generally passed unaltered from cell to cell, and from generation to generation.
Who coined the term epigenetics in 1941?
Conrad Waddington. Prefix, epi, means over, which suggests that some types of changes in gene expression are at a level that goes beyond changes in DNA sequences.
How do geneticists distinguish an epigenetic effect from other types of gene regulation?
An epigenetic effect begins with an initial event that causes a change in gene expression.
For example, DNA methylation may inhibit transcription. However, for this to be an epigenetic effect, the change must be passed from cell to cell and must not involve a change in the sequence of DNA.
What is the key feature of an epigenetic effect?
The long-term maintenance of a change in genetic expression.
As an example, let’s consider muscle cells in humans. Some genes in the human genome should be expressed in muscle cells, such as the genes that encode the proteins called actin and myosin, which are required for muscle contraction.
In embryonic muscle cells, these genes are subjected to epigenetic changes that promote their expression through adulthood. Alternatively, in other cell types, these same genes are inhibited by epigenetic changes such as DNA methylation. As the embryo grows and eventually becomes an adult, these epigenetic changes are passed from cell to cell so that adult muscle cells express actin and myosin genes at very high levels, whereas many other cell types do not.
T/F Some epigenetic changes, such as those involving the expression or inhibition of actin and myosin genes, are relatively permanent during the life of an individual.
True.
However, other epigenetic changes may be reversible during the life of an individual or may be reversible from one generation to the next.
What is the process in which certain species of plants require an exposure to cold temperatures in order to flower?
Vernalization
After vernalization, plants do not necessarily initiate flowering, but they acquire the ability to do so. Most commonly, plants are vernalized by exposure to cold winter temperatures and then flower the following spring or summer.
Vernalization involves epigenetic changes to genes that play a role in flowering. These epigenetic changes are induced by cold winter temperatures, and they are maintained during the flowering season. However, the epigenetic changes are reversed after the flowering season is over.
What is the study of mechanisms that lead to changes in gene expression that can be passed from cell to cell and are reversible, but do not involve a change in sequence of DNA?
Epigenetics.
This type of change may also be called EPIMUTATION.
This is a heritable change in gene expression that does not alter the sequence of DNA.
What is an epigenetic change that is passes from parent to offspring? An example is genomic imprinting.
Epigenetic inheritance
What is a case of epigenetic changes that are not inherited from parents?
For example, a person may be exposed to an environmental agent in cigarette smoke that causes an epigenetic change in a lung cell that is subsequently transmitted from cell to cell and promotes lung cancer. Such a change would not be transmitted to offspring.
What are the MOST common types of molecular changes that underlie epigenetic effects on gene expression?
- DNA methylation
- Chromatin remodeling
- Covalent histone modification
- Localization of histone variants
These types of changes are also involved in transient (nonepigenetic) gene regulation that is not transmitted from cell to cell.
The term which describes changes in gene expression that are not related to variations of the DNA sequence, yet are transmissible and are reversible, is __________
epigenetics or epigenetic
True or false: An epigenetic effect causes a change in gene expression without altering the sequence of DNA.
True false question.
True
False
True
Which of the following statements best describes epigenetic changes during the life of an individual?
Multiple choice question.
Some epigenetic changes are permanent while others are reversible.
All epigenetic changes are permanent and irreversible.
All epigenetic changes are transient and reversible.
Some epigenetic changes are permanent while others are reversible.
The molecular mechanisms of epigenetics are varied. The most common types are: DNA ________, chromatin ________, covalent ________ modification, and localization of histone variants.
Methylation, remodeling, and histone
Mendelian inheritance is characterized by three general rules: 1. Except in the case of rare _______, genes are passed unaltered from generation to generation; 2. Each gene obeys Mendel’s law of __________; and 3. During crosses, two or more genes obey Mendel’s law of independent __________-.
Mutations, segregation, assortment
What type of inheritance describes genomic imprinting?
Multiple choice question.
Mendelian
Extranuclear
Epigenetic
Mitochondrial
Epistatic
Epigenetic
Select all that apply
Which of the following statements are true regarding epigenetics?
Multiple select question.
Epigenetic changes may be transmitted to offspring.
Epigenetic changes are transmissible from cell to cell.
Variations of gene expression that result from DNA mutations
Variations are reversible from one generation to the next.
Variations of gene expression that are unrelated to DNA sequence variants
Epigenetic changes may be transmitted to offspring.
Epigenetic changes are transmissible from cell to cell.
Variations are reversible from one generation to the next.
Variations of gene expression that are unrelated to DNA sequence variants
Which of the following characterize an epigenetic effect?
Multiple select question.
The change must be passed from cell to cell
Leads to changes in the DNA sequence
Has no effect on gene expression
Causes a change in gene expression
The change must be passed from cell to cell
Causes a change in gene expression
[Information on Chromatin Modifications]
DNA methylation
Methyl groups may be attached to cytosine bases in DNA. When this occurs near promoters, transcription is usually repressed.
Chromatin remodeling
Nucleosomes may be moved to new locations or evicted. When such changes occur in the vicinity of promoters, the level of transcription may be altered. Also, larger-scale changes in chromatin structure may occur, such as those that happen during X-chromosome inactivation in female mammals, discussed later in this chapter.
Covalent histone modification
Specific amino acid side chains in the amino terminal tails of histones can be covalently modified. For example, they can be acetylated or phosphorylated. Such modifications may repress or activate transcription.
Localization of histone variants
Histone variants may become localized to specific locations, such as near the promoters of genes, and affect transcription.
None
[18.2 Epigenetics I: Genomic Imprinting]
What does the term imprinting implie?
A type of marking process that has memory.
For example, newly hatched birds identify marks on their parents, which allows them to distinguish their parents from other individuals.
What is the phenomenon in which a segment of DNA is imprinted, or marked, during egg or sperm formation in a way that affects gene expression throughout the life of the individual who inherits that DNA?
Genomic imprinting
However, depending on the gene, it may be marked by females during egg formation or by males during sperm formation, but not both. This marking process, which involves epigenetic modifications, affects whether or not the gene is expressed in the offspring.
What is dependent on how a particular gene is marked by one of the parents?
The offspring expresses either the maternal or the parental allele, but not both.
Does imprinting follow the Mendelian pattern of inheritance?
No, imprinted genes do not follow a Mendelian pattern of inheritance because imprinting causes the offspring to distinguish between maternal and paternal alleles.
Give some information on the first imprinted gene that was identified.
- Gene called Igf2, found in mice and other mammals.
- This gene encodes a growth hormone called insulin-like growth factor 2 (Igf2), which is needed for proper growth
- If a functional copy of this gene is NOT expressed, a mouse will be a dwarf.
[Remember] Mice are diploid meaning they have two copies of this gene, one from each parent.
How is a mutant allele, using Igf2 as an example, designated?
Igf2- (with a minus sign)
[Mice interaction with Lgf2- gene]
When a homozygous Igf2 Igf2 mouse and a homozygous Igf2−Igf2− mouse are crossed, the results are surprising.
If the female parent is homozygous for the mutant allele and the male parent is homozygous for the functional allele, all of the offspring grow to a normal size.
By contrast, if the female is homozygous for the functional allele and the male is homozygous for the mutant allele (right side), all of the offspring are dwarf.
Why is this surprising and give an explanation?
The mice have the same genotype yet they have different phenotypes!
In mice, the Igf2 gene is imprinted in such a way that only the paternal allele is expressed, which means it is transcribed into mRNA.
This breaks the laws of Mendelian inheritance.
If you crossed an Igf2 Igf2− male mouse to an Igf2 Igf2− female mouse, what would be the expected results?
Only the allele inherited from the father would be expressed in the offspring. Because he is heterozygous, half of the offspring would be normal size and half would be dwarf.
Why is the maternal gene encoding Igf2 not transcribed into mRNA?
DNA methylation, which is the attachment of methyl (—CH3) groups to bases of DNA, can alter gene transcription.
Researchers have discovered that DNA methylation is the marking process that occurs during the imprinting of certain genes, including the Igf2 gene.
For most genes, DNA methylation silences gene expression by inhibiting the initiation of transcription or by causing the chromatin in a region to become more compact. By contrast, for a few imprinted genes, DNA methylation may enhance gene expression by attracting activator proteins to the promoter or by preventing the binding of repressor proteins
True or false: As a result of genomic imprinting, individuals with the same genotype may have different phenotypes.
True false question.
True
False
True
True or false: Epigenetic changes that occur in an individual are permanent during its lifetime.
True false question.
True
False
False
The gene Igf2 encodes a(n) ______.
Multiple choice question.
growth hormone
transcription factor
enzyme
neurotransmitter
growth hormone
Select all that apply
Which of the following are common types of molecular changes that result in epigenetic effects on gene expression?
Multiple select question.
Covalent histone modification
DNA methylation
Localization of histone variants
DNA mutation
DNA translocation
Chromatin remodeling
Covalent histone modification
DNA methylation
Localization of histone variants
Chromatin remodeling
What does the expression of the Igf2 gene depend on in mice?
Multiple choice question.
Alleles inherited from both parents, with only the dominant gene expressed
Parental origin, with only the maternal gene expressed
Parental origin, with only the paternal gene expressed
Alleles inherited from both parents, with only the mutant gene expressed
Parental origin, with only the paternal gene expressed
Genomic imprinting is an example of a phenomenon called _________ inheritance.
epigenetic
Imprinted genes do not follow a Mendelian inheritance pattern because ______.
Multiple choice question.
the DNA sequence is altered in each generation
the alleles from the parents are expressed differently
individuals with imprinted genes are mosaics with different expression patterns in different somatic cells
the alleles from the parents are expressed differently
In mice, the Igf2 gene inherited from the ______ is not transcribed into mRNA because the DNA is ______.
Multiple choice question.
mother; methylated
father; methylated
mother; mutated
father; mutated
mother; methylated
Individuals may have the same genotype but very different phenotypes as a result of ______.
Multiple choice question.
polygenic inheritance
genetic linkage
genomic imprinting
epistasis
genomic imprinting
The marking process that occurs during genomic imprinting is the addition of ___________ groups to DNA.
methyl, CH3, or -CH3
One of the first imprinted genes to be identified was a gene in mice called Igf2. This gene encodes a growth hormone called ______-like growth ________ 2 (lgf2).
insulin, factor
The transcription of a gene can be altered by the attachment of _________ groups to the bases of DNA.
methyl, CH3, or -CH3
In mice, the Igf2 gene is imprinted in such a way that only the _________ allele is expressed.
paternal
Select all that apply
How does DNA methylation inhibit gene expression?
Multiple select question.
It attracts activator proteins to the promoter.
It causes mutations in the gene.
It prevents the initiation of transcription.
It prevents binding of repressor proteins.
It causes chromatin to become more compact.
It prevents the initiation of transcription.
It causes chromatin to become more compact.
Why don’t imprinted genes follow a Mendelian pattern of inheritance?
Multiple choice question.
Individuals may have the same genotype but different phenotypes because the offspring expresses only the maternal or paternal allele.
Imprinted genes are inherited only maternally because they are found on the mitochondrial genome.
The genes are linked on the same chromosome, violating Mendel’s law of independent assortment.
The genes do not separate during meiosis, violating Mendel’s law of segregation.
Individuals may have the same genotype but different phenotypes because the offspring expresses only the maternal or paternal allele.
How is the maternal version of the Igf2 gene silenced in mice?
Multiple choice question.
Methylation is erased from the gene, inhibiting transcription.
Methyl groups are attached to the gene, inhibiting transcription.
Compaction of one of the X chromosomes into a Barr body silences the gene.
The gene is found in mitochondria, which are only inherited from the father.
Methyl groups are attached to the gene, inhibiting transcription.
[18.3 Epigenetics II: X-Chromosome Inactivation]
What is a process that causes an X chromosome to become highly compacted and silences the genes that it carries?
X-chromosome inactivation (XCI)
Female mammals carry two X chromosomes in their cells, whereas males carry one X and one Y.
During embryonic development in female mammals, one of the X chromosomes undergoes an epigenetic change called X-chromosome inactivation (XCI). This process causes that X chromosome to become highly compacted, which silences the genes that it carries.
What were the two lines of evidence to indicate XCI?
First came from microscopic studies of mammalian cells.
In 1949, Canadian physicians Murray Barr and Ewart Bertram identified a highly condensed structure in the cells of female cats that was not found in the cells of male cats.
This structure was named a Barr body after one of its discoverers.
In 1960, Asian-American geneticist Susumu Ohno correctly proposed that a Barr body is a highly condensed X chromosome.
Lyon’s second line of evidence was the inheritance pattern of variegated coat colors in certain female mammals. A classic case is the calico cat, which has randomly distributed patches of black and orange fur.
What is a highly condensed X chromosome present in the cells of female mammals?
Barr body
How is the Barr body different from the other X chromosome in this cell?
The Barr body is much more compact than the other X chromosome in the cell. This compaction prevents most of the genes on the Barr body from being expressed.
How do we explain this patchwork phenotype in the calico cat?
According to Lyon’s hypothesis, the calico pattern is due to the permanent inactivation of one X chromosome in each cell that forms a patch of the cat’s skin.
The gene involved is an X-linked gene that occurs as an orange allele, XO, and a black allele, XB. A female cat heterozygous for this gene will be calico. (The cat’s white underside is due to a dominant allele of a different autosomal gene.)
At an early stage of embryonic development, one of the two X chromosomes is randomly inactivated in each of the cat’s somatic cells, including those that will give rise to the hair-producing skin cells. As the embryo grows and matures, the pattern of XCI is maintained during subsequent cell divisions.
Skin cells derived from a single embryonic cell in which the XB-carrying chromosome has been inactivated produce a patch of orange fur, because they express only the XO allele that is carried on the active chromosome. Alternatively, a group of skin cells in which the chromosome carrying XO has been inactivated express only the XB allele, producing a patch of black fur.
If female mammals are heterozygous for X-linked genes, approximately half of their somatic cells express one allele, whereas the rest of their somatic cells express the other allele. The result is an animal with randomly distributed patches of black and orange fur. These heterozygotes are called mosaics because they have somatic regions that are composed of two types of cells.
Addition of Information (Further explanation)
The calico pattern is due to random XCI in a female that is heterozygous for an X-linked gene with black (XB) and orange (XO) alleles. The cells at the top of this figure represent a small mass of cells making up the very early embryo. In these cells, both X chromosomes are active. At an early stage of embryonic development, one X chromosome is randomly inactivated in each cell. The initial inactivation pattern is an epigenetic change that is maintained in the descendants of each cell as the embryo matures into an adult. The pattern of orange and black fur in the adult cat reflects the pattern of XCI in the embryo.
For x-linked traits in humans, what will females who are heterozygous for recessive x-linked alleles usually show?
The dominant trait because the expression of the dominant allele in 50% of their cells is sufficient to produce the dominant phenotype.
How is it possible for a female who is heterozygous may show mild or even severe hemophilia symptoms when half of the cells should be expressing enough factor VIII for proper blood clotting?
X-chromosome inactivation in humans occurs when an embryo is 10 days old. At this stage, the liver contains only about a dozen cells. In most females who are heterozygous for the dominant and recessive (hemophilia-causing) alleles, roughly half of their liver cells express the dominant allele.
However, on rare occasions, all or most of the dozen embryonic liver cells may inactivate the X chromosome carrying the dominant functional allele. Following growth and development, such a female will have a very low level of factor VIII and as a result will show symptoms of hemophilia.
What is the phenomenon in which the expression of X-linked genes is equalized between males and females; in mammals, the inactivation of one X chromosome in the female reduces the number of expressed copies (doses) of X-linked genes from two to one?
Dosage compensation
What does the cells of humans and mammals have the ability to do when it comes to X chromosomes?
The ability to count the X chromosomes and allow only one of them to remain active.
Additional X chromosomes are converted to Barr bodies. In females, two X chromosomes are counted and one is inactivated. In males, one X chromosome is counted and none inactivated.
What is a short region on the X chromosome known to play a critical role in X inactivation?
X inactivation center (Xic)
Finnish-born American geneticist Eeva Therman and German-born American geneticist Klaus Patau determined that XCI is accomplished by counting the number of Xics and inactivating all X chromosomes except for one.
In cells with two X chromosomes, if one of them is missing its Xic due to a chromosome mutation, neither X chromosome will be inactivated, because only one Xic is counted. Having two active X chromosomes is a lethal condition for a human female embryo.
What is the gene responsible within the Xic that is required for compaction of the X chromosome into a Barr body?
This gene, discovered in 1991, is named Xist (for X inactive specific transcript). The Xist gene product is a long RNA molecule that does not encode a protein. Instead, the role of Xist RNA is to coat one of the two X chromosomes during the process of X-chromosome inactivation.
After coating, proteins associate with the Xist RNA and promote compaction of the chromosome into a Barr body. The Xist gene on the Barr body continues to be expressed after other genes on this chromosome have been silenced.
The expression of the Xist gene also maintains a chromosome as a Barr body during cell division. Whenever a somatic cell divides in a female mammal, the Barr body is replicated to produce two Barr bodies.
X-chromosome inactivation refers to the process that occurs in ______.
Multiple choice question.
all mammals, in which the genes of all X chromosomes are not expressed
female mammals, when the genes of one of the two X chromosomes are not expressed
male mammals, in which the genes of the single X chromosome are not expressed
female mammals, when the genes of both of the X chromosomes are not expressed
female mammals, when the genes of one of the two X chromosomes are not expressed
In genomic imprinting, the transcription of the imprinted gene is inhibited because ______.
Multiple choice question.
a transcription factor controlling gene expression is phosphorylated
the Xist transcript binds to the gene
the DNA is methylated
the DNA is phosphorylated
the DNA is methylated
What is a Barr body?
Multiple choice question.
An imprinted gene only found in females
A maternal cell that transports gene products into the developing egg
A highly condensed X chromosome
An inactive cell that is produced during oogenesis in female mammals
A region on the X chromosome that is essential for compaction
A highly condensed X chromosome
Which of the following phenotypes is directly associated with X-chromosome inactivation?
Multiple choice question.
Leaf color in four o’clock plants
Shell coiling in snails
Calico coat pattern in female cats
Skin pigmentation in humans
Body size in male mice
Calico coat pattern in female cats
The calico coat pattern in female cats is an example of ______.
Multiple choice question.
gene interaction due to linkage
extranuclear inheritance
paternal inheritance due to genomic imprinting
mosaicism due to X-chromosome inactivation
mosaicism due to X-chromosome inactivation
In the somatic cells of female mammals, the genes on one of the two copies of the X chromosome are not expressed. This phenomenon is known as X-chromosome __________
Blank 1: inactivation
Which of the following statements is true regarding a female mammal that is heterozygous for an X-linked gene?
Multiple choice question.
All of the somatic cells will express one of the two alleles.
Some of the somatic cells will express one allele, the others will express the other allele.
Three fourths (3/4) of the somatic cells will express one of the two alleles.
All of the somatic cells will express both of the two alleles at the same time.
Some of the somatic cells will express one allele, the others will express the other allele.
The process of X-chromosome inactivation is an example of a(n) _________ change that occurs during embryonic development in female mammals. This leads to the silencing of one of the two X chromosomes found in somatic cells.
epigenetic
In humans and other mammals, X chromosomes are counted. This process ensures that any normal somatic cell contains ________ active X chromosome(s).
one, 1, or single
A highly condensed X chromosome is known as a(n) ______ body.
Barr
[18.4 Epigenetics III: Effects of Environmental Agents]
What are the active fields in genetics in the study of environmental effects on epigenetics?
Two areas that have received a great deal of attention are the effects of diet and the potential effects of toxic agents, such as carcinogens—cancer-causing agents.
What has an effect that can promote epigenetic changes in the Agouti gene (designated A) found in mice?
Chemicals in the diet
This gene encodes the Agouti signaling peptide that controls the deposition of yellow pigment in developing hairs.
When mice are homozygous for a functional allele, AA, the expression of the gene promotes what?
The synthesis of pheomelanin, a yellow pigment.
During the growth of a hair, melanocytes, the pigment producing cells, within a hair follicle initially make what?
Eumelanin, which is black pigment.
What does the temporary or transient expression of the Agouti gene cause in the melanocytes, that typically make black pigment?
Causes them to make pheomelanin, a yellow pigment.
After the expression of the Agouti gene is over, these melanocytes revert back to creating black pigment.
What is the result of this transient gene, Agouti, and its influence on the melanocytes, the pigment-producing cells?
The result is a bad of yellow pigment sandwiched between layers of black pigment, which gives a brown color!
The yellow pigment is not synthesized new the tip of the hair, so the hair of AA mice is brown with black tips.
Different scenario, if a mouse is homozygous for a loss-of-function allele, aa, what color of fur will it have?
Since the Agouti gene will not express transiently, the fur of the mouse will be completely black because pheomelanin, the yellow pigment, will not be expressed by melanocytes.
Alternatively, a gain-of-function mutation that causes the Agouti gene to be overexpressed results in a mouse with yellow fur.
One such mutation is designated Avy. (A refers to Agouti, v refers to viable, and y refers to yellow. The letter v is used because other mutations in the Agouti gene are not viable.)
By characterizing the Avy allele at the molecular level, researchers determined that it is due to the insertion of a new promoter next to the normal promoter of the Agouti gene. This new promoter is very active, which causes the overexpression of the Agouti gene.
What are a variety of dietary factors, found in the diet, that can inhibit the enzyme DNA methyltransferase, which methylates DNA which, in turn, silences genes?
Folic acid, vitamin B12, and choline chloride.
How do we explain the results of mice, with different coat colors, and their dietary intake of factors that inhibit DNA methylation?
In the mice that are more yellow, the new promoter has undergone less DNA methylation. Therefore, the promoter remains active, leading to the transcription of the Agouti gene and the overproduction of yellow pigment. By contrast, the new promoter in the darker mice has undergone more methylation. Such methylation inhibits the overexpression of the Agouti gene and thereby prevents the overproduction of yellow pigment, resulting in darker fur.
What are some examples of identified correlations between epigenetic changes and particular diseases?
For example, some research studies have compared one variable, such as the level of DNA methylation of a specific gene, to a second variable, such as the severity of a disease. If a high level of DNA methylation is associated with an increase in disease severity, this is a positive correlation.
Researchers analyze the data to decide if such a correlation is statistically significant.
When a statistically significant correlation is obtained, how do we interpret its meaning?
Such a result suggests a true ASSOCIATION—changes in the two variables follow a pattern.
For example, in a positive correlation, when one variable increases, the other variable also increases.
What are three common ways an association can arise in reference to epigenetic changes and disease?
- The epigenetic changes directly contribute to the disease symptoms. There is a cause-and-effect relationship.
- Conversely, the disease symptoms may arise first, and then they cause subsequent epigenetic changes to happen. This is also a cause-and-effect relationship, but in the opposite direction.
- The association is indirect because a third factor is involved. For example, a toxic agent in the environment may cause a disease and also cause particular types of epigenetic changes even though those epigenetic changes do not contribute to the disease.
What are some examples of diseases that are associated with epigenetic changes? (5)
These include Alzheimer disease, cardiovascular diseases, diabetes, multiple sclerosis, and asthma.
For these diseases, further research is needed to determine if these epigenetic changes are directly contributing to the disease symptoms. The role of epigenetics in disease has been most extensively studied with regard to cancer.
[Information on - Environmental Agents that are Associated with Cancer and Are Known to Cause Epigenetic Changes]
Order = Environmental Agent, Occurrence, Associations with particular cancers
Polycyclic aromatic hydrocarbons
Tobacco smoke, automobile exhaust, charbroiled food
Lung, breast, stomach, and skin cancer
Benzene
Tobacco smoke, automobile exhaust
Leukemia, lymphoma, multiple myeloma
Endocrine disruptors (such as diethylstilbestrol)
Insecticides, fungicides, herbicides, some types of plastic
Breast, prostate, and thyroid cancer
Cadmium
Tobacco products, production of batteries
Lung and breast cancer
Nickel
Occupational exposure in mining, welding, and electroplating and in the manufacturing of jewelry, stainless steel, and batteries
Lung and nasal cancer
Arsenic
Lead alloy, feed additive in agriculture, insecticides
Skin, bladder, kidney, and liver cancer
None
In mice, the Agouti gene regulates ______.
Multiple choice question.
the inheritance pattern of mitochondria
the size of the individual
the sex of the individual
the transcription of cell cycling proteins
the deposition of yellow pigment in hair
the deposition of yellow pigment in hair
An example of X-chromosome inactivation is found in some female cats, which have a coat color containing randomly distributed patches of black and orange fur. This is called the _______ pattern of coat color.
calico
What is an example of mosaicism?
Multiple choice question.
Dextral coiling in snails
Dwarfism in mice
White chloroplasts in the four-o’clock plant
Calico coat pattern in cats
Calico coat pattern in cats
In statistics, changes in two variables that follow a pattern is termed a(n) ______.
Multiple choice question.
causation
concordance
correspondence
association
association
In a female mammal heterozygous for an X-linked recessive allele, what proportion of somatic cells will express the recessive allele?
Multiple choice question.
25%
0%
50%
100%
50%
In a eukaryotic cell, where are genes found?
Multiple select question.
the plasma membrane
the endoplasmic reticulum
chloroplasts
the nucleus
mitochondria
the Golgi apparatus
chloroplasts
the nucleus
mitochondria
Adult, wild-type mice with genotype AA for the Agouti gene will have what color coat hairs?
Multiple choice question.
All black
All brown
Yellow with brown tips
Brown with black tips
All yellow
Brown with black tips
[18.5 Extranuclear Inheritance: Organelle Genomes]
At what point in development is the segregation of genes explained by the pairing and segregation of homologous chromosomes?
Meiosis
T/F There are some genes that are not found on the chromosomes in cell nucleus, and these genes do not segregate in the same way.
True. Think mitochondria and chloroplasts.
What in eukaryotes, doe the transmission of genes happen outside the cell nucleus?
Extranuclear inheritance
Two important types of extranuclear inheritance patterns involve genes found in chloroplasts and mitochondria. Extranuclear inheritance is also called CYTOPLASMIC INHERITANCE because these organelles are in the cytoplasm of the cell.
Mitochondria and chloroplasts are found in eukaryotes because of what?
Ancient endosymbiotic relationship
They contain their own genetic material, called the mitochondrial genome and chloroplast genome, respectively
What type of DNA structure do mitochondria and chloroplasts have?
Single, circular DNA molecule.
What is a phenomenon in which offspring inherit particular genes only from the female parent (through the egg) and how was this phenomenon discovered?
Maternal Inheritance.
One of the first experiments showing an extranuclear inheritance pattern was carried out by German botanist Carl Correns in 1909. Correns discovered that leaf pigmentation in the four-o’clock plant (Mirabilis jalapa) follows a pattern of inheritance that does not obey Mendel’s law of segregation. Four-o’clock leaves may be green, white, or variegated.
Correns observed that the pigmentation of the offspring depended solely on the pigmentation of the female parent, a phenomenon called maternal inheritance
In cross 1, if the female parent providing the eggs had white leaves and the male parent providing the pollen had green leaves, all of the offspring had white leaves like the female parent. Correns also conducted a reciprocal cross—a cross in which the sexes and phenotypes are reversed compared to another cross.
What is a cross in which the sexes and phenotypes are reversed compared to another cross?
Reciprocal cross.
All this explains that in the first cross the female plant had white leaves that created white offspring in maternal inheritance.
For the second cross, he made a reciprocal cross, which he used a female plant with green leaves which produced green leaved offspring.
In the first cross, the other plant had green leaves. In the second cross (reciprocal), the other plant had white leaves.
Maternal inheritance in the four-o’clock plant. In four-o’clocks, the egg contains all of the proplastids, which develop into chloroplasts, that are inherited by the offspring. The phenotype of the offspring is determined by the maternal parent. The green phenotype is due to the presence of normal chloroplasts. The white phenotype is due to chloroplasts with a mutant allele that greatly reduces green pigment production. The variegated phenotype is due to a mixture of normal and mutant chloroplasts.
In this example, where is the gene located that causes the green color of four-o’clock leaves? How is this gene transmitted from parent to offspring?
The gene is located in the chloroplast DNA. In this species, chloroplasts are transmitted from parent to offspring via eggs but not via sperm.
How do we explain the variegated phenotype at the cellular level (reference to four-o’ clock plants)?
This phenotype is due to events that occur after fertilization. As a zygote containing both types of proplastids grows via cellular division to produce a multicellular plant, some cells may receive mostly protoplastids that develop into normal chloroplasts. Further division of these cells gives rise to a patch of green tissue. Alternatively, as a matter of chance, other cells may receive all or mostly mutant protoplastids that develop into chloroplasts that are defective in chlorophyll synthesis. The result is a patch of white tissue.
What is an inheritance pattern in which both the male and female gametes contribute organellar genes to the offspring?
Biparental inheritance
Which both the pollen and the egg contribute chloroplasts to the offspring.
What is a pattern in which only the male gamete contributes particular organellar genes to the offspring?
Paternal inheritance
T/F As with the transmission of chloroplasts in plants, maternal inheritance is the most common pattern of mitochondrial transmission in eukaryotes, although some species do exhibit biparental or paternal inheritance.
True
How is mitochondria in humans inherited?
Maternally
[Information of Examples of Human Mitochondrial Disease]
(These are usually chronic degenerative disorders that affect organs, such as the brain, eyes, heart, muscle, kidneys, and endocrine glands, whose cells require high levels of ATP.)
Leber’s hereditary optic neuropathy (LHON)
A mutation in one of several mitochondrial genes that encode electron transport proteins. The main symptom is loss of vision.
Neurogenic muscle weakness
A mutation in a mitochondrial gene that encodes a subunit of mitochondrial ATP synthase, which is required for ATP synthesis. Symptoms involve abnormalities in the nervous system that affect the muscles and eyes.
Maternal myopathy and cardiomyopathy
A mutation in a mitochondrial gene that encodes a tRNA for leucine. The primary symptoms involve muscle abnormalities, most notably in the heart.
Myoclonic epilepsy and ragged-red muscle fibers
A mutation in a mitochondrial gene that encodes a tRNA for lysine. Symptoms include epilepsy, dementia, blindness, deafness, and heart and kidney malfunctions.
None
The inheritance pattern observed for genes that are located outside the cell nucleus, in mitochondria or chloroplasts, is called ____________ inheritance.
extranuclear or cytoplasmic
Which of the following phenotypes is directly associated with X-chromosome inactivation?
Multiple choice question.
Leaf color in four o’clock plants
Calico coat pattern in female cats
Shell coiling in snails
Body size in male mice
Skin pigmentation in humans
Calico coat pattern in female cats
A true association occurs when ______.
Multiple choice question.
one variable is independent of another variable
two variables follow a pattern
one variable is caused by another variable
two variables are studied at the same time
two variables follow a pattern
In humans, mitochondria are inherited through a type of uniparental inheritance called _______ inheritance.
maternal
Which phenomenon describes the presence of two genes very close to each other on the same chromosome, and which are transmitted together as a unit?
Multiple choice question.
Epistasis
Linkage
Genomic imprinting
Pleiotropy
X inactivation
Linkage
[18.6 Genes on the Same Chromosome: Linkage and Recombination]
What happens when the alleles of different genes are on the same chromosome and do not independently assort?
A typical chromosome contains many hundreds or even a few thousand different genes. When two genes are close together on the same chromosome, they tend to be transmitted as a unit, a phenomenon known as LINKAGE.
What is a group of genes that usually stay together during meiosis?
Linkage group
In a two-factor cross, linked genes that are close together on the same chromosome do not follow the law of independent assortment.
How did Morgan explain his data while studying the transmission pattern of genes in crosses of fruit flies? (3)
When different genes are located on the same chromosome, the traits determined by those genes are more likely to be inherited together. This violates the law of independent assortment.
Due to crossing over during meiosis, homologous chromosomes can exchange pieces of chromosomes and create new combinations of alleles.
The likelihood of a crossover occurring in the region between two genes depends on the distance between the two genes. Crossovers between homologous chromosomes are much more likely to occur between two genes farther apart along a chromosome compared to two genes that are closer together.
What is an offspring whose combination of traits has not changed from the true-breeding parental generation?
Nonrecombinant
What is an offspring that has a different combination of traits from the true-breeding parental generation?
Recombinant
What is the use of genetic crosses to determine the linear order of genes that are linked to each other along the same chromosome?
Genetic mapping
What is a chart that shows the linear arrangement of genes along a chromosome?
Genetic Map
What is the frequency of crossing over between two genes?
Recombination frequency
This is accomplished by conducting a testcross. As an example, let’s refer back to the Drosophila testcross described in Figure 18.10. As we discussed, the genes for body color and wing shape are on the same chromosome. The recombinants are the result of crossing over during egg formation in the F1 female. We can use the data from the testcross shown in Figure 18.10 to estimate the distance between these two genes. The map distance between two genes is defined as the number of recombinants divided by the total number of offspring times 100.
What is the distance between genes along chromosomes, which is calculated as the number of recombinant offspring divided by the total number of offspring times 100?
Map distance
Select all that apply
Which of the following hypotheses did Thomas Hunt Morgan propose for the unexpected results he obtained when studying transmission of genes in Drosophila?
Multiple select question.
Some genes are located on extranuclear DNA and follow a maternal inheritance pattern, violating Mendel’s law of segregation.
Genes located on the same chromosome are more likely to be inherited together, violating Mendel’s law of independent assortment.
The likelihood of a crossover between genes is related to how far apart they are on the chromosome.
Alleles of different genes on the same chromosome are always inherited together.
Crossing over occurs during meiosis, allowing chromosomes to create new allele combinations.
Genes located on the same chromosome are more likely to be inherited together, violating Mendel’s law of independent assortment.
The likelihood of a crossover between genes is related to how far apart they are on the chromosome.
Crossing over occurs during meiosis, allowing chromosomes to create new allele combinations.
What is the phenomenon called in which a trait of the offspring is solely determined by the value of the trait in the female parent because it is passed on via the organelles in the egg cell?
Multiple choice question.
Gene linkage
Maternal inheritance
Maternal effect
Epistasis
Genomic imprinting
Maternal inheritance
Leaf pigmentation in four-o’clock plants is inherited via the chloroplast genome. A female plant with variegated leaves is crossed with a male plant with white leaves. What is the result of this cross?
Multiple choice question.
All offspring will have white leaves.
Some offspring will have green leaves, some will have white leaves, and some will have variegated leaves.
Half of the offspring will have variegated leaves, and the other half will have white leaves.
All offspring will have green leaves.
All offspring will have variegated leaves.
Some offspring will have green leaves, some will have white leaves, and some will have variegated leaves.
Which of the following statements most accurately defines epistasis?
Question 1 options:
A single gene affecting a single trait.
The inheritance of two or more genes close together on the same chromosome.
The genotype of the mother determining the phenotype of the offspring.
Inactivation of the allele from one parent and expression of the the allele from the other parent.
The alleles of one gene masking the dominant alleles of another gene.
The alleles of one gene masking the dominant alleles of another gene.
Sex-linked conditions are more common in men than in women because
Question 2 options:
men acquire two copies of the defective gene during fertilization.
the genes associated with the sex-linked conditions are linked to the Y chromosome, which determines maleness.
men need to inherit only one copy of the recessive allele for the condition to be fully expressed.
the sex chromosomes are more active in men than in women.
Men need to inherit only one copy of the recessive allele for the condition to be fully expressed.
Barr bodies
Question 3 options:
are formed only in males.
are formed in females.
inactivate Xic on autosomes.
cause an increased production of X-linked gene products.
are formed only in males and inactivate Xic on autosomes.
are formed in females.
A child has Type O blood. Which of the following cannot be the blood types of the parents?
Question 4 options:
O x O
O x AB
A x O
A x B
None of these could be the parents.
O x AB
Which of the following organelle(s) has/have a genome separate from the genome in the cell nucleus?
Question 5 options:
both the mitochondria and chloroplasts
both the mitochondria and the nucleolus
chloroplasts
mitochondria
nucleolus
both the mitochondria and chloroplasts
The DNA of fraternal twins is _____ identical.
Question 6 options:
75%
100%
50%
25%
0%
50%
Chloroplast and mitochondrial genes in mammals and plants are inherited from the mother.
Question 7 options:
False
True
True
A horticulturist is breeding a new variety of houseplant in which two genes control leaf color. G (allele for green) is dominant to g (yellow) and B (second allele for green) is dominant to b (yellow). The recessive homozygous condition of either gene will mask a dominant allele. What color is a plant with the genotype GgBb?
Question 8 options:
green
variegated (yellow and green spots or stripes)
yellow
an intermediate yellow-green
The color cannot be determined with the information given.
Green
A horticulturist is breeding a new variety of houseplant in which two genes control leaf color. G (allele for green) is dominant to g (yellow) and B (second allele for green) is dominant to b (yellow). The recessive homozygous condition of either gene will mask a dominant allele. What color is a plant with the genotype Ggbb?
Question 9 options:
an intermediate yellow-green
yellow
variegated (yellow and green spots or stripes)
green
The color cannot be determined with the information given.
Yellow
If 100 out of 1000 offspring are recombinants, then the recombination frequency is ___ and the genes are said to be ____ mu apart.
Question 10 options:
1%, 0.01
10%, 10
90%, 90
- 1%, 0.001
- 9%, .9
10%, 10
The genomes of mammalian mitochondria contain
Question 11 options:
genes whose products are used in translation of mRNA.
ribosomal genes.
genes for proteins used in oxidative phosphorylation.
a total of 37 genes.
All of the items listed are correct.
All of the items listed are correct.
Imagine in lemmings, that gray fur color (G) is dominant over white (g). There is another gene, called color, and individuals must have at least one “C” allele for gray color to be expressed. You obtain a white lemming that is heterozygous for gray fur color. What is its genotype?
ggcc
GgCC
gc
ggCc
Ggcc
Ggcc
In mice, the gene for insulin-like growth factor is imprinted. During embryonic development, only the paternal allele for insulin-like growth factor is expressed. This means
Question 13 options:
that the paternal allele is mutated.
that the maternal allele is expressed.
that the paternal allele is hyper-methylated.
that the paternal allele is imprinted.
that the maternal allele is imprinted.
that the maternal allele is imprinted.
Red-green colorblindness is a sex-linked trait on the X chromosome. A man with color-blindness and a woman with no history of color-blindness in either the males or females of her family plan to have children. What is the probability that a daughter born to this couple would be a carrier?
Question 14 options:
75%
25%
0%
50%
100%
25% WRONG
Paternal inheritance occurs in plants but not animals because plants have chloroplasts instead of mitochondria.
Question 15 options:
True
False
False
