Question 1

Hemophilia is caused by an X-linked recessive mutation in humans.If a woman whose paternal uncle (father's brother) was a hemophiliac marries a man whose brother is also a hemophiliac, what is the probability of their first child having hemophilia (Note: assume that there are no other cases of hemophilia in the pedigree and no hidden carriers)?
A)0
B)1/4
C)1/2
D)1/8
E)1

Accepted Answer

The answer of Hemophilia is caused by an X-linked recessive...

Question 2

A white-eyed female fruit fly is mated to a red-eyed male.One of their progeny is a white-eyed female.This white-eyed daughter likely arose from nondisjunction of the sex chromosomes during _________ in the __________.
A)meiosis I, mother
B)meiosis II, mother
C)meiosis I, father
D)meiosis II, father
E)meiosis I or II, mother

Accepted Answer

The answer of A white-eyed female fruit fly is mated...

Question 3

Which aspect(s) of chromosome behavior is/are primarily responsible for the tremendous amount of genetic variability associated with sexual reproduction?
A)Segregation of sister chromatids at anaphase II of meiosis
B)Segregation of homologous chromosomes at anaphase I of meiosis
C)Crossing over between homologous chromosomes during prophase I of meiosis
D)Independent alignment of different homologous pairs on the metaphase I spindle
E)Both crossing over between homologous chromosomes during prophase I of meiosis and independent alignment of different homologous pairs on the metaphase I spindle contribute to genetic variability

Accepted Answer

Both crossing over between homologous chromosomes during prophase I of meiosis and independent alignment of different homologous pairs on the metaphase I spindle contribute to genetic variability. Crossing over during prophase I of meiosis allows for exchange of genetic material between homologous chromosomes, while independent assortment during metaphase I allows for any combination of chromosomes to end up in a gamete. Together, these two factors lead to an immense amount of genetic diversity during sexual reproduction.

Question 4

Suppose you discover a new species of worm that exists in two forms-slimy and non-slimy.You find that mating slimy females to non-slimy males produces offspring consisting of slimy males and non-slimy females, whereas mating non-slimy females with slimy males produces offspring of both sexes that are all slimy.You would conclude that the _________ allele is dominant and that ________ are the heterogametic sex (the sex with two different sex chromosomes) in this species of worm.
A)slimy, females
B)slimy, males
C)non-slimy, females
D)non-slimy, males

Accepted Answer

This is an example of sex-linked inheritance, where the phenotype depends on which sex carries the dominant allele. Since mating slimy females with non-slimy males produces slimy males, the slimy allele must be dominant. Since offspring from non-slimy females and slimy males are all slimy, this indicates that the non-slimy allele is recessive. Additionally, the fact that offspring from the first mating combination have different phenotypes depending on their sex suggests that females have two different sex chromosomes (XX) while males have only one (XY), making females the heterogametic sex.

Question 5

What aspect of chromosome behavior most clearly accounts for Mendel's law of independent assortment?
A)Movement of sister chromatids to opposite poles at anaphase II of meiosis
B)Movement of homologous chromosomes to opposite poles at anaphase I of meiosis
C)Crossing over between homologous chromosomes during prophase I of meiosis
D)Replication of chromosomes prior to meiosis
E)Independent alignment of different homologous pairs on the metaphase I spindle

Accepted Answer

The independent alignment of different homologous pairs on the metaphase I spindle allows for the random segregation of different alleles during meiosis, which is the basis of Mendel's law of independent assortment. This is because each homologous pair can align independently, and the orientation of the chromosomes is random, resulting in a random assortment of maternal and paternal chromosomes in the gametes. The other choices do not directly relate to the independent assortment of chromosomes and therefore are not the best answers.

Question 6

What aspect of chromosome behavior most clearly accounts for Mendel's law of segregation?
A)Movement of sister chromatids to opposite poles at anaphase II of meiosis
B)Movement of homologous chromosomes to opposite poles at anaphase I of meiosis
C)Crossing over between homologous chromosomes during prophase I of meiosis
D)Replication of chromosomes prior to meiosis
E)Independent alignment of different homologous pairs on the metaphase I spindle

Accepted Answer

Mendel's law of segregation refers to the separation of alleles (variants of a gene) during gamete formation. This separation occurs when homologous chromosomes (which carry alleles of the same gene) separate and move to opposite poles during anaphase I of meiosis. This process is known as "disjunction" and is responsible for the random assortment of alleles into gametes. Movement of sister chromatids (A), crossing over (C), replication (D), and independent alignment (E) all contribute to genetic diversity, but do not directly account for Mendel's law of segregation.

Question 7

Mitosis results in _______ chromosome number, whereas meiosis results in _______ chromosome number.
A)a doubling of, no change in
B)no change in, no change in
C)a reduction by half in, no change in
D)no change in, a doubling of
E)no change in, a reduction by half in

Accepted Answer

Mitosis results in two daughter cells each having the same number of chromosomes as the parent cell, thus there is no change in chromosome number. Meiosis, on the other hand, results in four daughter cells each with half the number of chromosomes of the parent cell, thus reducing the chromosome number by half.

Question 8

Males with one copy of an X-linked gene are said to be _________ for that gene.
A)homozygous
B)heteroallelic
C)heterozygous
D)hemizygous
E)deficient

Accepted Answer

Males only have one copy of the X chromosome, so they are hemizygous for X-linked genes.

Question 9

Cells said to be in the G₀ stage A)have two chromatids per chromosome. B)are replicating their chromosomes. C)are about to enter the mitotic phase of the cell cycle. D)are in an extended G₁ phase and no longer cycling. E)are dead.

Accepted Answer

Cells in the G0 stage are in a resting or quiescent state where they have exited the cell cycle and are not actively preparing to divide. They are in an extended G1 phase and are not progressing through the cell cycle.

Question 10

Which of the following is not a property of homologous chromosomes? A)They pair physically during prophase of meiosis I. B)They exchange genes by crossing over during meiosis. C)They carry alleles for the same genes at the same chromosomal position. D)They are attached to the same centromere during G₂ of the cell cycle. E)They segregate to opposite poles at anaphase of meiosis I.

Accepted Answer

Homologous chromosomes have different centromeres and are not attached to the same centromere during the cell cycle. This is a characteristic of sister chromatids, which are identical copies of a single chromatid that are held together at the centromere until they are separated during mitosis or meiosis II.

Question 11

A white-eyed female fruit fly is mated to a red-eyed male.One of their progeny is a white-eyed female.What is the likely karyotype of this white-eyed daughter?
A)XX
B)XXY
C)XO
D)XXX
E)XYY

Accepted Answer

The white-eyed trait in fruit flies is X-linked recessive. For a female to be white-eyed, she must inherit two recessive alleles. The presence of a white-eyed female progeny from a red-eyed male suggests a nondisjunction event, leading to an XXY karyotype where the extra X carries the recessive allele.

Question 12

In chickens, it is the females that have two different sex chromosomes (Z and W) while the males have two Z chromosomes.A Z-linked gene controls the pattern of the feathers, with the dominant B allele causing the barred pattern and the b allele causing non-barred feathers.From which of the following crosses would all of the daughters be of one type (barred or non-barred) and all of the sons the other type?
A)barred females * non-barred males
B)non-barred females * barred males
C)non-barred females * non-barred males
D)barred females * barred males
E)More than one of the choices is correct.

Accepted Answer

The answer of In chickens, it is the females that...

Question 13

In fruit flies, brown eyes can be caused by the recessive mutations pn (prune), bw (brown) or ry (rosy), which are on the X chromosome, second chromosome, and third chromosome, respectively.Wild-type alleles for all three genes must be present for eyes to be red.Suppose that two brown-eyed flies are crossed and their progeny consist of brown-eyed sons and red-eyed daughters.Which mutation is responsible for the brown eyes in the parental female?
A)pn
B)bw
C)ry
D)either bw or ry
E)any of the three - pn, bw, or ry

Accepted Answer

The brown-eyed sons indicate that the mutation is on the X chromosome, as they inherit their X chromosome from their mother. Therefore, the mutation responsible is pn (prune), which is X-linked.

Question 14

A variable feature of some chromosomes in corn is the presence or absence of knobs at particular sites.Suppose that one member of each of two pairs of chromosomes in a corn plant has a knob.If this plant is crossed with a knobless plant, what percentage of the offspring is expected to be knobless?
A)100%
B)75%
C)50%
D)25%
E)0%

Accepted Answer

If one member of each of two pairs of chromosomes in a corn plant has a knob, it means that half of the chromosomes in that plant have knobs. When this plant is crossed with a knobless plant, all the gametes of the knobless plant will have no knobs, and only the gametes of the corn plant with knobs will have knobs. During fertilization, the offspring will randomly inherit one chromosome from each parent, so there's a 50% chance of inheriting a knobbed chromosome and a 50% chance of inheriting a knobless chromosome. Therefore, the expected percentage of offspring that is knobless is 50%, or 1/2. This is equivalent to 25% of the offspring having inherited two knobless chromosomes, which is the correct answer choice.

Question 15

Suppose you discover a new variant in which mice have spiky fur instead of the usual soft fur.You notice that this trait seems only to be present in males.To investigate this pattern, you cross a spiky-fur male with a soft-fur female, and find that all of the F₁ progeny of both sexes have soft fur.You then interbreed the F₁ and observe that all of the F₂ females have soft fur, but 1/4 of the F₂ males have spiky fur.You conclude that the spiky allele is A)an X-linked recessive. B)Y-linked. C)autosomal recessive with sex-limited expression. D)an X-linked dominant. E)an autosomal dominant with sex-limited expression.

Accepted Answer

The pattern of inheritance observed suggests that the spiky fur trait is autosomal recessive with sex-limited expression, meaning that the allele is located on an autosomal chromosome but its expression is influenced by sex hormones or other sex-specific factors. The fact that only males exhibit the spiky fur trait indicates that the allele is expressed only in the presence of male hormones or other factors specific to males. The 1:1 ratio of spiky:soft-fur males in the F₂ generation is consistent with a recessive trait that is carried on the X chromosome, as males inherit only one X chromosome from their mother and thus have no backup copy of the gene if it is defective. However, this is ruled out by the fact that all the females in the same generation have soft fur, indicating that they inherit a dominant allele from either parent that masks the expression of the spiky allele. Therefore, the most likely explanation is that the spiky allele is autosomal recessive with sex-limited expression.

Question 16

Cells in the G₂ stage of the cell cycle have ______ as cells of the same species in the G₁ stage. A)twice as many chromosomes B)twice as many chromatids C)half as many chromatids D)the same number of chromatids E)half as many chromosomes

Accepted Answer

The G₂ stage of the cell cycle represents the end of the S phase, where DNA replication has occurred, and each chromosome is now composed of two identical sister chromatids. Therefore, cells in this stage will have twice as many chromatids as cells in the G₁ stage, which represents the end of the G1 phase where each chromosome consists of a single chromatid. The number of chromosomes remains the same throughout the cell cycle.

Question 17

Color vision depends upon the dominant alleles of three genes: the R gene and the G gene are both on the X chromosome, while the B gene is autosomal.Recessive mutations in any of the three genes can cause color blindness.Suppose a colorblind man marries a colorblind woman and all of their offspring have normal vision.What is the genotype of the woman?
A)RRGGbb
B)RRggBB
C)rrGGbb
D)RRggBB or RRGGbb
E)rrGGbb or rrggBB

Accepted Answer

The answer of Color vision depends upon the dominant alleles...

Question 18

Red green color blindness is controlled by an X chromosomal gene in humans.A normal man and normal woman whose fathers are both color blind marry.What is the probability that their first child will be color blind?
A)1/2
B)1/4
C)1/8
D)1/3
E)0

Accepted Answer

Since the woman is normal, we can assume that she has two normal X chromosomes. However, since the father is color blind, he must have one color blind X chromosome and one normal Y chromosome. Therefore, all of their male children will be color blind (since they will inherit the color blind X chromosome from their father), and none of their female children will be color blind (since they will inherit a normal X chromosome from each parent). 
The probability of their first child being male is 1/2, and the probability of that male child being color blind is 1/2. Therefore, the overall probability of their first child being a color blind male is (1/2) x (1/2) = 1/4, which is option B.

Question 19

A cross between a white-eyed female fruit fly and a red-eyed male would generate which of the following types of progeny?
A)red-eyed females and white-eyed males
B)white-eyed females and red-eyed males
C)all red-eyed females and a 50:50 mixture of white-eyed and red-eyed males
D)all red-eyed males and a 50:50 mixture of white-eyed and red-eyed females
E)The result cannot be predicted because it depends on whether the female is homozygous or heterozygous

Accepted Answer

The answer of A cross between a white-eyed female fruit...

Question 20

Microtubules that attach to centrosomes but not chromosomes and that interdigitate with microtubules emanating from the centrosome at the opposite pole are known as
A)kinetochore microtubules.
B)polar microtubules.
C)astral microtubules.
D)interdigitating microtubules.
E)None of the choices is correct.

Accepted Answer

Polar microtubules attach to centrosomes but not directly to chromosomes and interact with microtubules from the opposite pole to help separate the poles during mitosis.

Quiz 4: The Chromosome Theory of Inheritance

A white-eyed female fruit fly is mated to a red-eyed male.One of their progeny is a white-eyed female.This white-eyed daughter likely arose from nondisjunction of the sex chromosomes during _ in the __.

Which aspect(s) of chromosome behavior is/are primarily responsible for the tremendous amount of genetic variability associated with sexual reproduction?

What aspect of chromosome behavior most clearly accounts for Mendel's law of independent assortment?

What aspect of chromosome behavior most clearly accounts for Mendel's law of segregation?

Mitosis results in _ chromosome number, whereas meiosis results in _ chromosome number.

Males with one copy of an X-linked gene are said to be _________ for that gene.

Cells said to be in the G₀ stage

Which of the following is not a property of homologous chromosomes?

A white-eyed female fruit fly is mated to a red-eyed male.One of their progeny is a white-eyed female.What is the likely karyotype of this white-eyed daughter?

A variable feature of some chromosomes in corn is the presence or absence of knobs at particular sites.Suppose that one member of each of two pairs of chromosomes in a corn plant has a knob.If this plant is crossed with a knobless plant, what percentage of the offspring is expected to be knobless?

Cells in the G₂ stage of the cell cycle have ______ as cells of the same species in the G₁ stage.

Red green color blindness is controlled by an X chromosomal gene in humans.A normal man and normal woman whose fathers are both color blind marry.What is the probability that their first child will be color blind?

A cross between a white-eyed female fruit fly and a red-eyed male would generate which of the following types of progeny?

Microtubules that attach to centrosomes but not chromosomes and that interdigitate with microtubules emanating from the centrosome at the opposite pole are known as