Chapter 16: Transmission of Genetic Information from Parents to Offspring II

Question 1

The Mendelian inheritance patterns follow three general rules. What are they?

16.1

Answer 1

1. except in the case of rare mutations, genes are passed unaltered from cell to cell, and from generation to generation
2. the genes obey Mendel’s law of segregation
3. for crosses involving two or more genes, the genes obey Mendel’s law of independent assortment

Question 2

Define epigenetic inheritance.

16.1

Answer 2

modification of a gene or chromosome during gamete formation that alters a gene’s expression but does not change the DNA sequence

Question 3

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?

16.6

Answer 3

linkage

Question 4

Epigenetics is the study of?

16.1

Answer 4

mechanisms that lead to changes in gene expression that can be passed from cell to cell, are reversible, but do not involve a change in the sequence of DNA

Question 5

What are some common types of molecular changes that can have an epigenetic effect that alters gene expression?

16.1

Answer 5

DNA methylation, chromatic remodeling, covalent histone modification, and localization of histone variants

Question 6

The phenomenon where offspring express a paternal or maternal allele depending on how a particular gene is marked is known as what?

16.2

Answer 6

genomic imprinting

Question 7

T or F: A gene can be marked by females during egg formation and by males during sperm production.

16.2

Answer 7

false; either or, not both

Question 8

Do imprinted genes follow a Mendelian pattern of inheritance?

16.2

Answer 8

No

Question 9

What is the function of the Igf2 imprinted gene?

16.2

Answer 9

it encodes a growth hormone called insulin-like growth factor 2; the mutation (Igf2-) blocks the function of the hormone

Question 10

Individuals may have the same genotype but very different phenotypes as a result of what?

16.2

Answer 10

genomic imprinting

Question 11

What serves as the marking process that occcurs during the imprinting of certain genes including Igf2?

16.2

Answer 11

DNA methylation

Question 12

Genomic imprinting refers to the:

16.2

Answer 12

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

Question 13

What is the function of DNA methylation in genomic imprinting?

16.2

Answer 13

it silences gene expression by inhibiting the initiation of transcription or by causing the chromatin in a region to become more compact

Question 14

Draw a diagram of genomic imprinting via DNA methylation in both females and males! :)

16.2

Answer 14

Question 15

A male mouse that is homozygous for the functional allel of the Igf2 gene is mated to a female that is heterozygous, carrying one functional copy and one mutant (nonfunctional) copy of the gene. What would be the expected outcome of this cross?

Answer 15

all normal size offspring (paternal allele is expressed)

Question 16

In the somatic cells of female mammals, the genes on one fo the two copies of the X-chromosome are not expressed. This phenomenon is known as?

16.3

Answer 16

X-chromosome inactivation

Question 17

T or F: During embyonic development in female mammals, one of the X chromosomes undergoes an epigenetic change called X-chromosome inactivation.

16.3

Answer 17

true

Question 18

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

16.3

Answer 18

two, because one active X chromosome is needed

Question 19

The short region on the X-chromosome where X-chromosome inactivation begins is called:

16.3

Answer 19

X-inactivation center (XiC)

Question 20

The Xist gene, which is involved in X inactivation, encodes what type of molecule?

16.3

Answer 20

RNA molecule

Question 21

The expression of a specific gene is required for the compaction of the X chromosome into a Barr body. Which gene is this?

16.3

Answer 21

Xist gene (X inactive specific transcript)

Question 22

Which statement regarding X-chromosome inactivation is false?

a. Xic is the site where X-chromosome inactivation begins
b. Xic is where the Xist gene is located
c. The Xist gene on the inactivated X chromosome (the Barr body) is not expressed
d. The product of the Xist gene coats the inactivated X chromosome

16.3

Answer 22

c. The Xist gene on the inactivated x chromosome (the Barr body) is not expressed

Question 23

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?

16.3

Answer 23

all of the X chromosomes are inactivated except for one

Question 24

The Xist gene product is a long ____ molecule that ________ for a protein.

16.3

Answer 24

RNA; does not code

Question 25

How is the Xist gene involved in X inactivation? ## Footnote 16.3

Answer 25

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

Question 26

T or F: Cells of humans and other mammals have the ability to cunt X chromosomes and allow only one X chromosome to be active. ## Footnote 16.3

Answer 26

true

Question 27

When mice carrying the Avy allele exhibit a darker coat color, this phenotype is thought to be caused by dietary factors that result in... ## Footnote 16.4

Answer 27

a greater level of DNA mehtylation and a decrease in the expression of the Agouti gene

Question 28

When an association occurs between an environmental agent that causes an epigenetic change and a particular disease, this association can be due to what factors? ## Footnote 16.4

Answer 28

1. the epigenetic change directly contributes to the disease symptoms 2. the disease symptoms arise first, and they cause subsequent epigenetic changes to happen 3. the association is indirect because a third factor is involved

Question 29

Which organelles demonstrate extranuclear inheritance? ## Footnote 16.5

Answer 29

chloroplast and mitochondria

Question 30

What is encoded by the Xist gene of the X chromosome? ## Footnote 16.3

Answer 30

an RNA molecule

Question 31

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 orgnanelles in the egg cell? ## Footnote 16.5

Answer 31

maternal inheritance

Question 32

What accounts for the wide array of coat color seen in mice carrying the A vy allele of the Agouti gene? ## Footnote 16.5

Answer 32

epigenetic modification of the new promoter of the Agouti gene

Question 33

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? ## Footnote 16.5

Answer 33

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

Question 34

In most plant species, chloroplasts are inherited via which cell? Why? ## Footnote 16.5

Answer 34

they are inherited via the egg cell, because it contributes most of the cytoplasm to the zygote

Question 35

Chloroplats are inherited only from the pollen in ____ inheritance. ## Footnote 16.5

Answer 35

paternal

Question 36

In plants, which gamete typically provides most of the cytoplasm to the zygote? ## Footnote 16.5

Answer 36

the egg cell

Question 37

What is extranuclear inheritance? ## Footnote 16.5

Answer 37

the transmission of genes located outside the nucleus

Question 38

What types of organs are most liley to be affected by mitochondrial disease? ## Footnote 16.5

Answer 38

organs that require high ATP levels

Question 39

Who performed a two-factor cross in sweet peas that involved flower color and pollen shape? ## Footnote 16.6

Answer 39

Bateson and Punnett

Question 40

Bateson and Punnet, 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... ## Footnote 16.6

Answer 40

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

Question 41

If two genes are linked, is it possible for recombinant offspring to occur? ## Footnote 16.6

Answer 41

yes, if crossing over occurs