Question 1

Suppose you discover a new species of worm that exists in two forms-slimy and non-slimy.You find that mating slimy females with 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.

Accepted Answer

The fact that mating slimy females with non-slimy males produces offspring with a slimy phenotype indicates that the slimy allele is dominant, as all the offspring have the slimy phenotype. Additionally, the fact that mating non-slimy females with slimy males produces offspring that are all slimy indicates that the slimy allele is present on the sex chromosome, and that females are the heterogametic sex (as the offspring of non-slimy females and slimy males are all of the same sex and have the slimy phenotype). This means that the slimy allele is on the X chromosome, and that males are XY and females are XX.

Question 2

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 nonbarred feathers.From which of the following crosses would all of the daughters be of one type (barred or nonbarred)and all of the sons the other type?

Accepted Answer

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

Question 3

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 _________.

Accepted Answer

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

Question 4

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

Accepted Answer

The fact that the spiky fur trait is only present in males suggests that it is sex-limited in its expression. The fact that it is not present in the F1 generation suggests that it is recessive, and the fact that it appears in 1/4 of the F₂ males but in none of the females (who all have soft fur) suggests that it is an autosomal recessive trait with sex-limited expression. Therefore, the best choice is C, an autosomal recessive with sex-limited expression.

Question 5

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?

Accepted Answer

Since the progeny consists of brown-eyed sons and red-eyed daughters, the mutation causing brown eyes in the parental female must be on the X chromosome. The pn (prune) mutation is the only one located on the X chromosome, making it responsible for the brown eyes in the parental female.

Question 6

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

Accepted Answer

Polar microtubules attach to the centrosomes but not the chromosomes and interdigitate with microtubules from the opposite pole, providing stability and separation of the two poles during cell division. Kinetochore microtubules attach to the chromosomes and pull them towards the poles, while astral microtubules radiate outwards from the centrosome and play a role in positioning the spindle during cell division. Interdigitating microtubules is not a commonly used term in the context of microtubule organization during cell division.

Question 7

In Drosophila,the recessive allele for forked bristles is sex-linked,and the recessive allele for purple eyes is autosomal.The wild-type alleles are for straight bristles and red eyes,respectively.A female,heterozygous for both pairs of alleles,is mated with a male with forked bristles and purple eyes.What percentage of the daughters will have forked bristles and purple eyes?

Accepted Answer

Since the gene for forked bristles is sex-linked and the female is heterozygous, she will pass on the allele for forked bristles to half of her daughters. The gene for purple eyes is autosomal recessive, and since the female is heterozygous and the male has purple eyes, half of their offspring will inherit the purple eyes phenotype. Therefore, 1/2 (for forked bristles) * 1/2 (for purple eyes) = 1/4 or 25% of the daughters will have both forked bristles and purple eyes.

Question 8

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

Accepted Answer

Since the woman is normal, she must have two X chromosomes that are both normal. The man must have one X chromosome that is normal and one X chromosome that carries the gene for color blindness. 
The Punnett square for their offspring would be:

| | XN | Xn | 
|---|---|---|
|Y |XYN |XYn |
|Y |XYN |XYn |

As we can see, 1 out of 4 possible combinations would result in a color-blind child (XYn). Therefore, the probability of their first child being color-blind is 1/4 or 0.25. Thus, the correct choice is B.

Question 9

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

Accepted Answer

Mitosis results in two daughter cells each having the same number of chromosomes as the parent cell, thus "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 "a reduction by half in" chromosome number.

Question 10

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

Accepted Answer

In fruit flies, the gene for eye color is located on the X chromosome, with red eyes being dominant (X^R) and white eyes being recessive (X^r). Since the female is white-eyed, she must have two recessive alleles (X^rX^r) and the male, being red-eyed, has at least one dominant allele but only one X chromosome (X^RY). Their offspring would result in red-eyed females (X^RX^r) due to receiving one X chromosome from each parent, and white-eyed males (X^rY) because they inherit the X chromosome with the recessive allele from their mother and the Y chromosome from their father, with no dominant allele to mask the recessive white-eyed gene.

Question 11

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

Accepted Answer

Mendel's law of segregation states that during gamete formation, the two alleles for a trait separate, with only one allele present in each gamete. This is due to the separation of homologous chromosomes during anaphase I of meiosis, with each gamete receiving only one member of each homologous pair.

Question 12

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

Accepted Answer

Males have only one X chromosome, therefore they are hemizygous for X-linked genes. Homozygous and heterozygous refer to individuals with two copies of a gene, and heteroallelic is not a term used for X-linked genes. Deficient is not the correct term for describing the genetic status of males with one copy of an X-linked gene.

Question 13

A female fruit fly with singed bristles was mated with a male from a true-breeding wild-type stock with long bristles.All of the F₁ females had wild-type bristles and all of the F₁ males had singed bristles.If the F₁ flies are intercrossed,the expected ratio of long to singed bristles in the F₂ flies is

Accepted Answer

The answer of A female fruit fly with singed bristles...

Question 14

Cells said to be in the G₀ stage

Accepted Answer

The answer of Cells said to be in the G₀...

Question 15

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 offspring?

Accepted Answer

The white-eyed female offspring likely has a karyotype of XXY. In fruit flies, the white-eye trait is X-linked recessive. A white-eyed female (XwXw) mated with a red-eyed male (X+Y) can produce a white-eyed female offspring if nondisjunction occurs, resulting in an XXY karyotype.

Question 16

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

Accepted Answer

Homologous chromosomes are paired during meiosis I, exchange genes by crossing-over, carry alleles for the same genes at the same chromosomal position, and segregate to opposite poles during anaphase of meiosis I. However, they are not attached to the same centromere during metaphase of meiosis I; instead, they are attached to homologous centromeres (one from each chromosome).

Question 17

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?

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 18

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

Accepted Answer

In the G₂ stage, cells have replicated their DNA during the S phase, resulting in twice as many chromatids compared to the G₁ stage, where DNA replication has not yet occurred.

Question 19

Haemophilia is caused by an X-linked recessive mutation in humans.If a woman whose paternal uncle (father's brother)was a haemophiliac marries a man whose brother is also a haemophiliac,what is the probability of their first child having haemophilia? Assume that there are no other cases of haemophilia in the pedigree and no hidden carriers.

Accepted Answer

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

Question 20

Colour 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 colour blindness.Suppose a colour-blind man marries a colour-blind woman and all of their offspring have normal vision.What is the genotype of the woman?

Accepted Answer

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

Quiz 2: Extensions to Mendels Laws

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 _.

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

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

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

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

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

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

Cells said to be in the G₀ stage

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 offspring?

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

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.

Quiz 2: Extensions to Mendels Laws

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 _________.

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

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

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

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

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

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

Cells said to be in the G0 stage

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 offspring?

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

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.

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 _.

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

Cells said to be in the G₀ stage

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