Chapter 18 Epigenetics Inheritance

The inheritance pattern observed for genes that are located outside the cell nucleus, in mitochondria or chloroplasts,___________ is called inheritance.

extranuclear

The gene Igf2 encodes a(n) Blank______.

growth hormone

In a testcross performed on fruitflies, a ______.

heterozygous female is crossed with a homozygous recessive male

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 like growth factor

Determining the linear order and the distance between genes on the same chromosome is the purpose of genetic

map

The transcription of a gene can be altered by the attachment of_______--groups to the bases of DNA.

methyl

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

mother; methylated

Offspring that do not differ from the parental generation in their combination of traits are known as parentals or

nonrecombinants

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

permanent

The chi square formula is best described as ______.

squaring the difference between each observed and expected value, dividing each by the expected value, and summing all values

In experiments with Drosophila, a(n)____________ involves mating heterozygous females with males that are homozygous for recessive alleles.

testcross

In genomic imprinting, the transcription of the imprinted gene is inhibited because Blank______.

the DNA is methylated

If a chi square test for goodness of fit performed with data from a two-factor cross returns a P value < 0.01, Blank______.

the null hypothesis is rejected

Which of the following values of the chi square test would be most likely to suggest that the null hypothesis is true, and so cannot be rejected?

0.5731

A scientist collects data from a two-factor cross with a null hypothesis that four different types of offspring will be produced in a 1:1:1:1 ratio. After calculating the chi square value using the chi square test for goodness of fit, the scientist must look up the corresponding p value. The number of degrees of freedom she will use when analyzing the chi square table is

3

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

An RNA molecule

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

Barr body

Which organelles demonstrate cytoplasmic inheritance?

Chloroplasts Mitochondria

The cells of humans and other mammals are able to inactivate all but one of the X chromosomes, because these cells have the ability to ___________their X chromosomes.

Count

People who have abnormalities in the number of X chromosomes may exhibit some phenotypic abnormalities. How come?

Effects of gene expression prior to X chromosome inactivation Incomplete silencing of genes on Barr bodies

What types of egg cells can be produced from a plant with variegated leaves?

Egg cells with normal proplastids Egg cells with a combination of normal and mutant proplastids Egg cells with mutant proplastids

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-chromosome inactivation?

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

Males with Klinefelter syndrome have an XXY chromosome composition. How many Barr body bodies would be found in the cells of such males?

One

In cats, one X allele results in dark fur and another results in orange fur. In an orange fur patch on a calico cat, which X chromosome is inactivated?

The X chromosome with the allele for dark fur.

In the majority of plants, which gamete provides most of the cytoplasm to the zygote?

The egg cell

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

The gene Igf2 in mammals

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.

Which of the following statements are true regarding epigenetics?

Variations are reversible from one generation to the next. Epigenetic changes are transmissible from cell to cell. Variations of gene expression that are unrelated to DNA sequence variants Epigenetic changes may be transmitted to offspring.

What structure found in the egg gives rise to chloroplasts in leaf cells?

What structure found in the egg gives rise to chloroplasts in leaf cells?

What observations did Carl Correns make when studying the four-o'clock plant (Mirabilis jalapa), leading him to discover maternal inheritance?

When the maternal plant had white leaves, the offspring always had white leaves. When the maternal plant had green leaves, the offspring always had green leaves. When the maternal plant had variegated leaves, the offspring were green, white, or variegated.

If two genes are linked, is it possible for recombinant offspring to occur?

Yes, if crossing over occurs.

The proplastids in the egg cell of a plant are the precursors of

chloroplasts

In the four-o'clock plant, mutant proplastids in the egg cell will produce ______.

chloroplasts with very little pigment

Thomas Hunt Morgan recognized that some genes in Drosophila violated the law of independent assortment. He proposed that such genes were located on the same chromosome and that new combinations of alleles could be created only if _____________ ______________occurred during meiosis.

crossing over

Epigenetic inheritance refers to epigenetic changes that occur Blank______.

during gamete formation

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?

Some offspring will have green leaves, some will have white leaves, and some will have variegated leaves.

Which of the following best describes the null hypothesis of a chi square test?

There is no real difference between the observed and expected data.

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

Two, because one active X chromosome is needed.

A true association occurs when ______.

two variables follow a pattern

How does a calico cat obtain its unique coat pattern?

A female cat is heterozygous for black and orange fur. X inactivation randomly silences one of the alleles, causing patches of black and orange fur.

What is a Barr body?

A highly condensed X chromosome

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.

Individuals with 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 characterize an epigenetic effect?

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 inactivation

The molecular mechanisms of epigenetics are varied. The most common types are: DNA _________, chromatin________ , covalent__________ modification, and localization of histone variants.

DNA methylation Chromatin Remodeling Covalent histone modification Localization of histone variants

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

In genomic imprinting, which genes are silenced?

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

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?

Linkage

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?

Maternal inheritance

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

Methyl groups are attached to the gene, inhibiting transcription.

Female mammals that are heterozygous for X-linked genes, and are thus composed of two types of cells, are known as which of the following?

Mosaics

Which of the following hypotheses did Thomas Hunt Morgan propose for the unexpected results he obtained when studying transmission of genes in Drosophila?

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. Genes located on the same chromosome are more likely to be inherited together, violating Mendel's law of independent assortment.

Modification of a gene or chromosome during gamete formation that alters a gene's expression but does not change the DNA sequence is known as__________ inheritance.

epigenetic

The process of X-chromosome inactivation occurs during embryonic development in female mammals and leads to the silencing of one of the two X chromosomes found in somatic cells. This is an example of a(n)______________change.

epigenetic

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

epigenetic

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

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 Blank______.

genomic imprinting

Bateson and Punnett, and later Morgan, did experiments on the transmission of genes in various organisms. Their results did not conform to Mendel's law of independent assortment because they observed Blank______.

many more F2 offspring with the parental combination of traits than predicted

Some female mammals are composed of two different types of cells because they are heterozygous for X-linked genes and experience X inactivation. This phenomenon is best described by the term

mosaics

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

transcription

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

transcription; compact

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 ______ is not produced.

yellow pigment pheomelanin