Question 1

Which of the following best describes the difference between heterogametic and homogametic sexes in humans?

Accepted Answer

Homogametic individuals produce gametes with the same sex chromosome (XX in females), while heterogametic individuals produce gametes with different sex chromosomes (XY in males).

Question 2

During meiosis, the X and Y chromosomes pair due to the presence of which region?

Accepted Answer

PAR (pseudoautosomal) region

Question 3

A male with an X-linked recessive disorder inherited the mutant allele from:

Accepted Answer

His mother

Question 4

In Drosophila, a red-eyed female is crossed with a white-eyed male. All F1 offspring have red eyes. What does this indicate about the inheritance of the white-eye trait?

Accepted Answer

Red-eye is dominant and X-linked.

Question 5

Which of the following best explains why reciprocal crosses involving X-linked traits do not yield the same results as those involving autosomal traits?

Accepted Answer

Because males are hemizygous for the X chromosome and inherit their X chromosome from their mother.

Question 6

A woman who is heterozygous for an X-linked dominant disorder (genotype $X^A X^a$) has children with an unaffected man ($X^a Y$). What is the probability that a son will be affected?

Accepted Answer

$0.25$

Question 7

Which of the following statements about X-linked recessive inheritance in humans is correct?

Accepted Answer

Affected mothers pass the trait to all their sons.

Question 8

A color-blind woman (X-linked recessive) and a man with normal vision have a daughter. What is the probability that the daughter will be color-blind?

Accepted Answer

$1.0$

Question 9

In a human pedigree, an X-linked recessive trait is observed to skip generations and is more common in males. Which of the following best explains this pattern?

Accepted Answer

Males are hemizygous for the X chromosome, so a single recessive allele will cause the phenotype.

Question 10

A man with an X-linked dominant disorder has children with a woman who does not carry the allele. What proportion of his daughters will be affected?

Accepted Answer

$1.0$

Question 11

Which of the following is true regarding the inheritance of the SRY gene?

Accepted Answer

It is located on the Y chromosome and determines male development.

Question 12

If a red-eyed female Drosophila (homozygous) is crossed with a white-eyed male, what is the expected phenotype ratio in the F1 generation?

Accepted Answer

All red-eyed offspring

Question 13

A man with Duchenne muscular dystrophy (an X-linked recessive disorder) has children with a woman who is not a carrier. What is the probability that their son will have the disorder?

Accepted Answer

$0$

Question 14

Which of the following best describes a reciprocal cross?

Accepted Answer

A cross in which the phenotypes of the parents are reversed with respect to sex.

Question 15

In a pedigree, an X-linked recessive trait is present in a female. Which of the following must be true about her father?

Accepted Answer

He must be affected.

Question 16

A woman who is a carrier for an X-linked recessive disorder ($X^N X^n$) and a man who is unaffected ($X^N Y$) have a child. What is the probability that a son will be affected?

Accepted Answer

$0.5$

Question 17

Which of the following is NOT a feature of X-linked recessive inheritance?

Accepted Answer

Affected fathers always pass the trait to all their sons.

Question 18

In Drosophila, if a white-eyed female is crossed with a red-eyed male, what is the expected phenotype of the male offspring in the F1 generation?

Accepted Answer

All white-eyed males

Question 19

Which of the following best explains why X-linked traits are more commonly expressed in males than in females?

Accepted Answer

Males are hemizygous for the X chromosome, so a single recessive allele will result in the phenotype.

Sex Linkage and X-Linked Inheritance Patterns CH 3 sex linkage

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