Chapter 4 Study Guide Flashcards by Alexandra Lugo

Dosage compensation is a mechanism that _____.

equalizes the amount of protein produced by X-linked genes in the two sexes

equalizes the effects of X-linked genes relative to autosomal genes

equalizes the effects of Y-linked genes relative to autosomal genes

ensures that a dose of a drug is the same for males and females

ensures that the amount of protein produced by a Y-linked gene is the same as the amount produced by an X-linked gene

equalizes the amount of protein produced by X-linked genes in the two sexes

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A man with a hereditary skin condition has 10 children with a phenotypically normal woman who is homozygous for the normal allele; 5 of the children are normal boys and 5 are girls who all have the same skin condition as their father. Which of the following is the most likely genetic basis for the skin condition?

X-linked dominant

autosomal recessive

X-linked recessive

autosomal dominant

Y-linked

X-linked dominant

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Females inherit a Z-linked trait from _____.

their mother only

their father only

their mother and their father

their mother or their father

None of the above answers is correct

their father only

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In the XX-XO sex-determination system, which of the following is true?

The ratio of the number of X chromosomes divided by the number of haploid sets of autosomes determines the sex of the offspring.

The temperature during embryonic development determines the sex of the offspring.

The presence of the Y chromosome determines the male sex, while the absence of the Y chromosome determines the female sex.

The presence of only a single X chromosome determines the male sex, while the presence of two X chromosomes determines the female sex.

The presence of only a single X chromosome determines the female sex, while the presence of two X chromosomes determines the male sex.

The presence of only a single X chromosome determines the male sex, while the presence of two X chromosomes determines the female sex.

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Fruit flies with XXY sex chromosomes and all other chromosomes normal in number have which sexual phenotype?

metamale

intersex

female

male

Metafemale

female

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A male with normal sex chromosomes has how many Barr bodies?

Because all but one X chromosome are inactivated and becomes Barr bodies, males usually have 0 Barr bodies.

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Which cross would result in a female white-eyed fruit fly? (The gene for white eyes is represented as “w”.)

XX * XwY

XXw * XYw

XXw * XY

XXw * XwY

XwXw * XY

XXw * XwY

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Assume that a man carries an X-linked dominant mutation. His wife is heterozygous for the same mutation. What is the expected frequency of this dominant trait among their children?

all of their sons will be normal and all of their daughters will be affected

all of their sons will be affected and all of their daughters will be normal.

all of their daughters will be affected; ½ of their sons will be normal and ½ will be affected

all of their sons will be normal; ½ of their daughters will be normal and ½ will be affected.

all of their daughters will be normal; ½ of their sons will be normal and ½ will be affected

all of their daughters will be affected; ½ of their sons will be normal and ½ will be affected

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A man and a woman who both have normal vision have a daughter with the sex-linked recessive condition of red-green color blindness. The daughter is also short and has folds of skin on the neck. Chromosome analysis of the daughter would likely reveal that she has which of the following chromosome constitutions?

XXX

XXY

XO
XO is Turner syndrome, characterized by short stature and neck skin folds, and the daughter is hemizygous for the mutant allele.

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The Lyon hypothesis proposes that _____.

X-linked recessive traits display cross-cross inheritance

the expression of autosomal genes increases in males

each Barr body is an inactivated X chromosome

the Y chromosome contains very little genetic information

males inherit their X chromosome from their mother

each Barr body is an inactivated X chromosome

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A woman who is homozygous for the sex-linked recessive condition of red-green color blindness marries a man with normal vision. Among their possible children, which of the following would you expect not to see?

a boy with normal vision

a girl with normal vision

a colorblind boy

a girl who is heterozygous for the colorblind allele

All of the above would normally be expected to occur.

a boy with normal vision

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If a male bird that is homozygous for a recessive Z-linked mutation is crossed to a wild-type female, what proportion of the progeny will be mutant males?

100%

25%

75%

50%

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In which of the following chromosome constitutions would you expect to find one Barr body in the nuclei of somatic cells?

XXX

XYY

XXXY

XXY

XO (O represents a missing chromosome)

XXY
The number of Barr bodies is one less than the number of X chromosomes. The presence of the Y chromosome has no effect on the number of Barr bodies.

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Why are few characteristics in humans Y-linked?
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Answer choices

The Y chromosome is smaller in size and thus has less genes affecting less traits.

Only roughly 50% of the human population has a Y chromosome, so the number of characteristics seen are reduced.

Genes on the Y chromosome are only expressed during development, so few characteristics remain through adulthood.

Since all humans have at least one X chromosome, the genes from this chromosome mask any genes found on the Y chromosome.

The Y chromosome is only found in gametes.

The Y chromosome is smaller in size and thus has fewer genes affecting fewer traits.

Because the Y chromosome of many organisms contains little genetic information, most sex-linked characteristics are X linked. Males and females differ in their sex chromosomes, so the pattern of inheritance for sex-linked characteristics differs from that exhibited by genes located on autosomes.

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During meiosis, the Y chromosome undergoes recombination with _____________, which may help preserve some functions and prevent total degeneration of the Y chromosome.

itself

the X chromosome

nothing, (The Y chromosome does not undergo recombination.)

an autosome

a Barr body

Itself

The Y chromosome slowly degenerated, losing DNA and genes until it became greatly reduced in size and contained little genetic information. This degeneration produced the Y chromosome found in males today.

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An individual with Turner syndrome has how many Barr bodies?
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Answer choices

Because individuals with Turner syndrome usually have a single X chromosome, and all but one X chromosome are inactivated and become Barr bodies, these individuals usually have 0 Barr bodies.

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A man carries the allele for red-green color blindness on his X chromosome. Such a man is described by which of the following terms?

hemizygous

holandric

heterozygous

homozygous

homogametic

hemizygous

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Fruit flies with XXYYY sex chromosomes and all other chromosomes normal have which sexual phenotype?

metafemale

metamale

intersex

female

male

female

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A triple-X (XXX) individual has how many Barr bodies?

2
Because triplo-X individuals usually have three X chromosomes and all but one X chromosome are inactivated and become Barr bodies, these individuals usually have 2 Barr bodies.

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In sequential _____, each individual animal is both male and female, but not at the same time.

XX-XO sex determination

genic sex determination

ZZ-ZW sex determination

XX-XY sex determination

hermaphroditism

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Assume that a mutation occurs in the XIST gene of a XY male that makes the gene inactive. What would you expect would be the phenotypic consequences of this mutation for the male?

He would have enhanced expression of his Y-linked genes.

He would probably have no phenotypic consequences.

He would probably not survive because all his X-linked genes would be turned off.

He would not have expression of some of his autosomal genes.

He would have several female phenotypic characteristics since his Y chromosome would be inactivated.

He would probably have no phenotypic consequences.

The XIST gene is involved in X inactivation and with XY males the X remains active.

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When T.H. Morgan crossed the mutant male fruit fly with white eyes to normal females with red eyes, he found in the F1 offspring mostly _____.

both males and females had white eyes

both males and females with red eyes

females with white eyes and males with red eyes

males with white eyes and females with red eyes

half the males and females with white eyes with the other half of both sexes with red eyes

both males and females with red eyes

The F1 females would be heterozygous for this sex-linked condition and the males will be hemizygous for the normal allele.

A eukaryotic diploid cell from an organism with the XX-XO sex determination system has two pairs of autosomes and one X chromosome. One pair of autosomes has a heterozygous locus with alleles A and a. The other pair of autosomes has a heterozygous locus with alleles B and b. What is the probability of a gamete from this individual having the following genotype: alleles a and b, without chromosome X?

⅛

⅙

1/16

⅛

The probability of a gamete containing a is ½, containing b is ½ and not containing the X is ½ so ½ × ½ × ½ = 1/8.

Fruit flies with XX sex chromosomes and three haploid sets of autosomes (AAA) have which sexual phenotype?

intersex

female

metafemale

metamale

male

intersex

Women with androgen insensitivity syndrome _____. have two Y chromosomes (XYY) have an inactive SRY gene have testes that produce testosterone have two X chromosomes and a Y (XXY) have an XX chromosome constitution but carry the SRY gene on one of the X chromosomes

have testes that produce testosterone

What is the probability that the first son born of a woman heterozygous for the sex-linked recessive condition of red-green color blindness and a man with normal vision will be color blind? ½ 0 ⅔ ¼ ⅛

1/2 Males inherit their X chromosome from their mother, and half of these X chromosomes will carry the mutant allele.

Which statement does not explain why tortoiseshell cats are usually female? because cats have three copies of the X chromosome because of X inactivation in females because males only have one copy of the X-linked locus for orange color because the gene for the presence of orange color is on the X chromosome

because cats have three copies of the X chromosome

In humans, is a father able to pass along a Y-linked trait to his daughter? Yes, the daughter inherits one sex chromosome from each parent. Yes, if the inherited Y chromosome does not become a Barr body. No, the father would have passed another X chromosome to his daughter. Yes, since there is not another Y chromosome to compensate for the mutation, the trait would be displayed in the daughter. No, the X chromosome from the mother would inhibit expression of the Y-linked trait.

No, the father would have passed another X chromosome to his daughter.

What is the mechanism by which sex is established? sex–determination sex–influenced sex–linkage Lyon hypothesis dosage compensation

sex-determination

In bearded dragons, sex is determined by which characteristic? sex chromosomes only X and Y chromosomes temperature only both sex chromosomes and temperature genes scattered throughout on the nonsex chromosomes (autosomes)

both sex chromosomes and temperature

In the XX‑XO mechanism of sex determination, which of the statements is true? Males have one X chromosome and one Y chromosome (XY). Males have two X chromosomes (XX) and females have one X chromosome (XO). Females have two X chromosomes (XX) and males have one X chromosome (XO). Females have two Z chromosomes and males have one Z chromosome (ZO). Males have one chromosome (XO) at high temperatures and two X chromosomes at low temperatures (XX).

Females have two X chromosomes (XX) and males have one X chromosome (XO).

With the genic sex‑determination mechanism, which of the statements is true? More than one of these is true. Females have one Z and one W chromosome (ZW) and males have two Z chromosomes (ZZ). Sex is determined by genes on undifferentiated chromosomes. Females have two X chromosomes (XX) and males have one chromosome (XO). Females have two X chromosomes (XX) and males have one X and one Y chromosome (XY).

Sex is determined by genes on undifferentiated chromosomes.

A fruit fly, Drosophila melanogaster, that has only one sex chromosome (XO) and two sets of autosomes would have which sexual phenotype? male metafemale metamale intersex female

male

In humans, what normally results in the male sexual phenotype? the presence of the Xist gene on the X chromosome the presence of two Z chromosomes (ZZ) the presence of one X chromosome and one W chromosome (XW) the presence of the SRY gene on the Y chromosome the presence of only one X chromosome (XO)

the presence of the SRY gene on the Y chromosome

Humans with only one sex chromosome (XO) usually have underdeveloped sexual characteristics and are sterile. What is this condition called? Nondisjunction Klinefelter syndrome Lyon hypothesis Androgen–insensitivity syndrome Turner syndrome

Turner Syndrome

The white‑eyed mutation in Drosophila, studied by Thomas Hunt Morgan, was the first clear case of sex‑linked inheritance. When Morgan crossed a white‑eyed female with a red‑eyed male, what phenotypes were present in the offspring? All of the males had white eyes and all of the females had red eyes. All of the females had white eyes and all of the males had red eyes. All of the offspring had red eyes. All of the offspring had white eyes. One‑half of both females and males had red eyes and one‑half had white eyes.

All of the males had white eyes and all of the females had red eyes.

Normally in humans, a mutant gene on the Y chromosome will be inherited in which way? All of the daughters of a parent with the mutant gene will receive it but none of the sons will. All of the sons of a parent with the mutant gene will receive it but none of the daughters will. Half of the sons and daughters of a parent with the mutant gene will receive it and half will not. One‑quarter of both the sons and the daughters of a parent with the mutant gene will receive it and the rest will not. Half of the sons of a parent with the mutant gene will receive it and half will not; none of the daughters will receive it.

All of the sons of a parent with the mutant gene will receive it but none of the daughters will.

Which term describes the situation, for X‑linked genes, in human and Drosophila males who have only one X chromosome? homogametic heterozygous homozygous hemizygous dioecious

hemizygous

X-linked red–green color blindness in humans is a recessive condition. Which statement is true? A color‑blind man must have had a color‑blind mother. A color‑blind woman must have had a color‑blind mother. A color‑blind man must have had a color‑blind father. A color‑blind woman must have had a color‑blind father. A man with normal vision cannot have had a color‑blind father.

A color‑blind woman must have had a color‑blind father.

In chickens, the females are heterogametic, ZW, and the males are homogametic, ZZ. Most sex‑linked genes are only carried on the Z chromosome. Congenital baldness is caused by a recessive sex‑linked allele. If a bald male is crossed to a normal female, what would be the expected results in the offspring? All the offspring will be normal regardless of sexual phenotype. All the females will be normal and all the males will be bald. All the offspring will be bald regardless of sexual phenotype. Half the offspring will be bald and half will be normal regardless of sexual phenotype. All the males will be normal and all the females will be bald.

All the males will be normal and all the females will be bald.

In the evolution of the mammalian Y chromosome, which is assumed to have occurred? It evolved from an X chromosome found in some birds. It evolved from an ancestral Y chromosome found in insects such as Drosophila. It evolved from the fusion of two X chromosomes. It evolved from a Barr body that underwent multiple rounds of replication. It evolved from an autosome.

It evolved from an autosome.

A human male with the chromosome constitution of XXXYY would contain how many Barr bodies in his somatic cells? 1 0 4 2 3

What did Mary Lyon propose about sex chromosomes in mammals? One X chromosome in each female cell becomes inactivated, and the process of selection is random. The X and Y chromosomes will pair with each other during meiosis in males. Genes on the Y chromosome are expressed at very high levels. The female sexual phenotype will normally result from having two X chromosomes in mammals. The Y chromosome determines the male sexual phenotype in mammals.

One X chromosome in each female cell becomes inactivated, and the process of selection is random.

The results of which of these crosses allowed T. H. Morgan to conclude that the white‑eye trait in Drosophila was not autosomal recessive? None of the crosses would give a different result than what would be expected if the white‑eye trait was autosomal recessive. crosses between true-breeding white‑eyed females and red‑eyed males crosses between true‑breeding white‑eyed females and white‑eyed males crosses between true‑breeding red‑eyed females and red‑eyed males crosses between true‑breeding red‑eyed females and white‑eyed males

crosses between true-breeding white‑eyed females and red‑eyed males

Because the white‑eye trait is X‑linked recessive, what result would you expect when crossing a heterozygous red‑eyed female with a red-eyed male? All females will have red eyes whereas half of the males will have red eyes and half will have white eyes. All males will be red-eyed whereas half of the females will have red eyes and half will have white eyes. All females will be red‑eyed and all males will be white‑eyed. In both sexes, half of the offspring will have red eyes and half of the offspring will have white eyes. All offspring will be red-eyed.

All females will have red eyes whereas half of the males will have red eyes and half will have white eyes.

Since the white‑eye trait is X‑linked recessive, what result would you expect when crossing a heterozygous red‑eyed female with a white‑eyed male? all red‑eyed progeny In each sex, half of the offspring will have red and half of the offspring will have white eyes. all red‑eyed females and all white‑eyed males all red‑eyed females with half of the males having white and half of the males having red eyes all red‑eyed males with half of the females having white and half of the females having red eyes

In each sex, half of the offspring will have red and half of the offspring will have white eyes.

If the white‑eye trait were X‑linked dominant rather than X‑linked recessive, what result would you expect when crossing a heterozygous white‑eyed female with a red‑eyed male? For each sex, half of the offspring will have red eyes and half of the offspring will have white eyes. All female offspring will be red‑eyed, whereas half of the male offsping will have white eyes and half of the male offspring will have red eyes. All female offspring will be red‑eyed and all male offspring will be white‑eyed. All male offspring will be red‑eyed, whereas half of the female offspring will have white eyes and half of the female offspring will have red eyes. All offspring will be red‑eyed.

For each sex, half of the offspring will have red eyes and half of the offspring will have white eyes.

If the white-eye trait were X‑linked dominant, rather than X‑linked recessive, what result would you expect when crossing a heterozygous white‑eyed female with a white‑eyed male? All female offspring will be white-eyed, whereas half of the male offspring will have white eyes and half of the male offspring will have red eyes. For each sex, half of the offspring will have red eyes and half of the offspring will have white eyes. All male offspring will be red‑eyed, whereas half of the female offspring will have white eyes and half of the female offspring will have red eyes. All offspring will be red‑eyed. All female offspring will be red‑eyed, whereas half of the male offspring will have white eyes and half of the male offspring will have red eyes.

All female offspring will be white-eyed, whereas half of the male offspring will have white eyes and half of the male offspring will have red eyes.

If the white‑eye trait were Y‑linked dominant, rather than X‑linked recessive, what result would you expect when crossing a red‑eyed female with a white‑eyed male? For each sex, half of the offspring will have red eyes and half of the offspring will have white eyes. All female offspring will be red‑eyed and all male offspring will be white‑eyed. All male offspring will be red‑eyed male, whereas half of the female offspring will have white eyes and half of the female offspring will have red eyes. All offspring will be red‑eyed. All female offspring will be white‑eyed, whereas half of the male offspring will have white eyes and half of the male offspring will have red eyes.

All female offspring will be red‑eyed and all male offspring will be white‑eyed.

Calvin Bridges determined that the rare white‑eyed males produced from the mating of true‑breeding red‑eyed females with white‑eyed males resulted from a nondisjunction of X chromosomes in the female parent during meiosis. If such a mating produced 1234 red‑eyed progeny and three white‑eyed males, what is the observed rate of nondisjunction of the X chromosomes? This is impossible to calculate with the given information. 0. 97% 0. 49% 0. 24% 0. 12%

0.24%

If nondisjunction of X chromosomes occurs at a rate of 2% in a certain population of Drosophila, approximately how many white‑eyed males would you expect to see among 1000 offspring resulting from breeding a true‑breeding red‑eyed female with a white‑eyed male? 2 20 10 5 This is impossible to calculate with the given information.

In the animation, the rare white‑eyed males generated from offspring of true‑breeding red‑eyed females and white‑eyed males were the result of a nondisjunction of X chromosomes in the female during meiosis I. Could white‑eyed males be generated in this cross by a nondisjunction of X chromatids in the female during meiosis II? Why or why not? No, if a nondisjunction of X chromatids occurred in meiosis II of a female, all progeny would have red eyes. Yes, because a nondisjunction of X chromatids in meiosis II of a female will generate two abnormal gametes, one with two X chromosomes and one with no X chromosome. No, if a nondisjunction of X chromatids occurred in meiosis II of a female, only white-eyed females could be generated. No, if a nondisjunction of X chromatids occurred in meiosis II of a female, none of the resulting offspring would be viable. Yes, because a nondisjunction of X chromatids in meiosis II of a female will result in both white-eyed males and white-eyed females.

Yes, because a nondisjunction of X chromatids in meiosis II of a female will generate two abnormal gametes, one with two X chromosomes and one with no X chromosome.