BIO 1 (Chpt 18)

X-chromosome inactivation refers to the process that occurs in

female mammals, when the genes of one of the two X chromosomes are not expressed.

The calico pattern in cats is due to random X-chromosome inactivation in a

female that is heterozygous for an X-linked gene with black (XB) and orange (XO) alleles.

The inheritance pattern of the Igf2 gene in mice, in which only the paternal gene is expressed, is known as:

genomic imprinting

The gene Igf2 encodes a(n)

growth hormone

A male with a deletion of the Xic region of his X chromosome will display what phenotype

he will have no apparent phenotype associated with the mutated Xic region.

In cats, the calico pattern is caused by the random X-chromosome _______ in females that are heterozygous for an X-linked gene with black and ______ alleles.

inactivation orange

People who have abnormalities in the number of X chromosomes may exhibit some phenotypic abnormalities due to:

incomplete silencing of genes on Barr bodies effects of gene expression prior to X inactivation

Genomic imprinting refers to the

marking of DNA so that the phenotype of offspring depends on the parental origin of the gene.

The marking process that occurs during genomic imprinting is the addition of

methyl groups to DNA.

In mice, the Igf2 gene inherited from the ______ is not transcribed into mRNA because the DNA is ______.

mother; methylated

In humans and other mammals, X chromosomes are counted. This process ensures that any normal somatic cell contains _______ active X chromosome(s).

one

In triple X syndrome, how many X chromosomes are converted into Barr bodies and why?

one, because two active X chromosomes are needed

If the Agouti gene in mice undergoes a gain-of-function mutation, the gene will be

over-expressed, resulting in yellow fur.

What does the expression of the Igf2 gene depend on in mice?

parental origin, with only the paternal gene expressed

In mice, the Igf2 gene is imprinted in such a way that only the

paternal allele is expressed.

female with deletion of the Xic region of one of her X chromosome will display what phenotype

she will produce twice as much protein as normal x chromosomes.

Researchers have identified several mutations that affect the expression of the Agouti gene in mice, including the loss-of-function gene a. For example, mice that are aa homozygotes will have black fur because

the yellow pigment pheomelanin is not produced.

For most genes, DNA methylation silences genes by inhibiting the initiation of ______ or by causing the chromatin in a region to become more ______.

transcription; compact

Turner Syndrome

A chromosomal disorder in females in which either an X chromosome is missing, making the person XO instead of XX, or part of one X chromosome is deleted. 0 Bar bodies

What is an example of mosaicism?

Calico coat pattern in cats

In cats, the calico pattern is caused by the random X-chromosome ______ in females that are heterozygous for an X-linked gene with black and _______ alleles.

Inactivation, Orange

Epigentics

Reversible Changes In gene expression passed from cell to cell.

normal Female

XX

Which of the following is an example of an imprinted gene?

the gene Igf2 in mammals

The process that is directly affected by the attachment of methyl groups to the bases of DNA is

transcription.

Arrange the events that occur during the establishment of imprinting. Begin at the top with zygote formation.

1. After fertilization somatic cells, retain the methylation pattern inherited from the parents. 2. During gamete formation the methylation pattems are erased. 3. A gene is methylated either in sperm or egg cells.

Klinefelter syndrome

A chromosomal disorder in which males have an extra X chromosome, making them XXY instead of XY. 1 barr body

People experiencing Turner, triple X, or Klinefelter syndrome experience symptoms associated with abnormalities in the number of their X chromosomes. What are some reasons posited for this?

Although all but one X chromosome is inactivated, some genes on the Barr body may remain active. The symptoms may be associated with genes expressed prior to Barr body formation.

Which of the following best describes an epimutation?

An inherited change in gene expression without a corresponding change in the gene's DNA sequence

A highly condensed X chromosome is known as a(n)

Barr Body

If two X chromosomes are present in a mammalian cell, one of them is converted to a(n)

Barr Body

In a mammalian cell that contains two X chromosomes, one of the X chromosomes will become a(n)

Barr Body

The cells of humans and other mammals have the ability to __________ their X chromosomes, and are therefore able to inactivate all but one of them.

Count

Genomic imprinting is an example of a phenomenon called ______ inheritance.

Epigenetic

Changes in gene expression that are not related to variations of the DNA sequence, yet are transmissible and are reversible

Epigenetics

A(n) ______ is a heritable change in gene expression that does not alter the sequence of DNA.

Epimutation

Epigenetic changes that occur in an individual are permanent during its lifetime.

False

In genomic imprinting, which genes are silenced?

Genes inherited from either the mother or the father depending on the gene.

Which of the following statements are true regarding genomic imprinting?

It is permanent in the somatic cells of an individual. Marking of the DNA is altered from one generation to the next.

How does DNA methylation inhibit gene expression?

It prevents the initiation of transcription. It causes chromatin to become more compact.

How is the Xist gene involved in X inactivation?

It synthesizes RNA, which coats one of the X chromosomes. Proteins then associate with the RNA, promoting compaction into a Barr body.

Which of the following statements are true regarding genomic imprinting?

Marking of the DNA is altered from one generation to the next. It is permanent in the somatic cells of an individual.

How is the maternal version of the Igf2 gene silenced in mice?

Methyl groups are attached to the gene, inhibiting transcription.

In genomic imprinting, the imprinting pattern in somatic cells of an individual is:

Permanent

Localization Of Histone Variants

Promoters of Genes are Disrupted by the movement of Histone variants affecting transcription.

Which of these sequences plays a critical role in Barr body formation?

The X inactivation center (Xic)

How is X inactivation accomplished?

The Xics are counted, allowing the cell to inactivate all but one X chromosome.

The relationship between loci and linkage That Morgan described is

The closer together two genes are on a chromosome, the more likely they will be inherited together.

What evidence did Mary Lyon have when she proposed the concept of X-chromosome inactivation?

The presence of a highly condensed structure in the cells of female mammals, which was possibly a condensed X chromosome. Some female mammals exhibited a complex pattern of inheritance of coat colors, such as that observed in calico cats.

DNA Methylation

Transcription is represented when menthol groups attach to cytosine Bases In DNA.

An epigenetic effect causes a change in gene expression without altering the sequence of DNA.

True

Which of the following statements are true regarding epigenetics?

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.

The region on the X chromosome that is known to play a role in Barr body formation

X inactivation center

Normal Male

XY 0 bar bodies

The compaction of the x chromosome into a Barr body arises from the actions of which gene?

Xist

The process of X-chromosome inactivation involves the gene ______, which encodes a very long ______ molecule. This molecule coats one of two X chromosomes, thus starting a process that ultimately leads to compaction of the chromosome into a Barr body.

Xist ; RNA

X inactivation is accomplished when all of the ______ are counted, allowing the cell to recognize and inactivate all but one of the X chromosomes.

Zics

What is encoded by the Xist gene of the X chromosome?

an RNA molecule

Epigenetic inheritance refers to epigenetic changes that occur

during gamete formation.

Triple X Syndrome

A genetic abnormality in which a female has an extra X sex chromosome; characterized by decreased fertility, some genital abnormality, and slight mental retardation. 2 bar bodies

Some people are born with abnormalities in the number of their sex chromosomes. For example, people born with triple X syndrome have three X chromosomes, and those born with Klinefelter syndrome have two X chromosomes and one Y. How does X inactivation proceed in these cases?

All of the X chromosomes are inactivated except for one.

Epigentic Effects

Causes a change in gene expression The change must be passed from cell to cell

The observation by scientists of a highly condensed structure found in the cells of female cats that may be one of the X chromosomes and the observation of the complex pattern of coat color inheritance in calico cats led Mary Lyon to propose the phenomenon of X

Chromosome and Activation

During gamete formation, the old methylation patterns of imprinted genes are ___________. New methylation patterns are established depending on whether the individual is a female or a male.

Erased

During gamete formation, the old methylation patterns of imprinted genes are_______ . New methylation patterns are established depending on whether the individual is a female or a male.

Erased

How Can crossing Over Maintain The Principle Of Independent Assortment For Alleles Present On The Same Chromosome?

For two genes located far apart on the same chromosome, crossing over essentially unlinks the genes, and the genes assort independently.

The phenomenon where offspring express a paternal or maternal allele depending on how a particular gene is marked is known as ______ imprinting.

Genomic

In what type of inheritance pattern are phenotypes dependent on the parental origin of the alleles?

Genomic Imprinting

Epigenic Inheritance

Includes a Subset Of Epigenetic Changed That Are passed From parent to offspring accords generations.

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 (Igf2).

Insulin, Factor

maternal inheritance of lorganelles maternal inheritance is the typical pattern of inheritance for mitochondria and chloroplasts because

Mitochondria And chloroplasts cone from large cytoplasm Of the egg rather than the relatively minuscule cytoplasm Of The sperm.

female mammals that are composed of two different types of cells because they are heterozygous for X-linked genes and experience X inactivation

Mosaics

Chromatin Remodeling

Nucleosomes move to new locations or are evicted in the vicinity of promoters altering transcription.

Which of the following statements best describes epigenetic changes during the life of an individual?

Some epigenetic changes are permanent while others are reversible

Which of the following statements is true regarding a female mammal that is heterozygous for an X-linked gene?

Some of the somatic cells will express one allele, the others will express the other allele.

Covalent Histone Modification

Specific Amino Acid Side Chains In Amino Acid Tails Of Histone Are Phosphorylated.

genomic imprinting

a phenomenon in which expression of an allele in offspring depends on whether the allele is inherited from the male or female parent

Adult, wild-type mice with genotype AA for the Agouti gene will have what color coat hairs?

brown with black tips

Which of the following phenotypes is directly associated with X-chromosome inactivation?

calico coat pattern in female cats

The observation by scientists of a highly condensed structure found in the cells of female cats that may be one of the X chromosomes and the observation of the complex pattern of coat color inheritance in calico cats led Mary Lyon to propose the phenomenon of X

chromosome inactivation

A barr body is typically found in the

female somatic cells

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

inactivation

Female mammals that are heterozygous for X-linked genes, and are thus composed of two types of cells,

mosaics