Question 1

Which of the following best explains why white-eyed female fruit flies are less common than white-eyed males in Morgan's experiments?

Accepted Answer

Females must inherit two copies of the white-eye allele (one from each parent) because the gene is X-linked recessive.

Question 2

A male fruit fly has the genotype $$X^wY. $$What is the expected phenotype?

Accepted Answer

White eyes, because there is no dominant allele on the Y chromosome to mask the recessive X-linked allele.

Question 3

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

Accepted Answer

Females express X-linked recessive traits only if they are homozygous for the allele.

Question 4

If a woman is a carrier for hemophilia (an X-linked recessive disorder) and her partner is unaffected, what is the probability that their son will have hemophilia?

Accepted Answer

$$0.25$$

Question 5

Which process during meiosis is primarily responsible for genetic recombination between linked genes?

Accepted Answer

Crossing over between homologous chromosomes

Question 6

A genetic map is constructed using recombination frequencies. If two genes are 10 map units apart, what is the expected recombination frequency between them?

Accepted Answer

$$0.10$$

Question 7

Which of the following chromosomal alterations results in a chromosome with a segment that is repeated?

Accepted Answer

Duplication

Question 8

A child is born with Down syndrome, which is caused by trisomy 21. Which meiotic error most likely led to this condition?

Accepted Answer

Nondisjunction during meiosis I or II

Question 9

Which of the following best describes the inheritance pattern of mitochondrial DNA?

Accepted Answer

It is inherited only from the mother.

Question 10

If a female is heterozygous for an X-linked gene, what is the expected effect of X-inactivation in her somatic cells?

Accepted Answer

One X chromosome is randomly inactivated in each cell, leading to mosaic expression.

Question 11

Which of the following scenarios would most likely result in a polyploid organism?

Accepted Answer

Fertilization of an egg by two sperm

Question 12

A male with Klinefelter syndrome has the karyotype $$XXY. $$Which of the following best explains how this karyotype could arise?

Accepted Answer

Nondisjunction of sex chromosomes during meiosis in either parent

Question 13

Which of the following is a consequence of a reciprocal translocation?

Accepted Answer

A segment of one chromosome is exchanged with a segment of a nonhomologous chromosome.

Question 14

In a dihybrid cross between $$YyRr$$ and $$yyrr ($$where Y = yellow, y = green, R = round, r = wrinkled), what percentage of the offspring are expected to have parental phenotypes?

Accepted Answer

$$50\%$$

Question 15

Which of the following best describes the relationship between gene linkage and recombination frequency?

Accepted Answer

The closer two genes are on a chromosome, the lower the recombination frequency.

Question 16

Which of the following is an example of an X-linked recessive disorder in humans?

Accepted Answer

Hemophilia

Question 17

Which of the following events during meiosis can lead to aneuploidy?

Accepted Answer

Nondisjunction of homologous chromosomes during meiosis I

Question 18

Which of the following statements about Barr bodies is correct?

Accepted Answer

A Barr body is an inactivated X chromosome found in the nuclei of female mammalian cells.

Question 19

Which of the following best explains why mitochondrial disorders are inherited maternally?

Accepted Answer

Mitochondria in the zygote are derived almost exclusively from the egg cell.

Chromosomal Basis of Inheritance and Genetic Disorders

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