Question 1

Which of the following best explains why dominant lethal alleles are much rarer in populations than recessive lethal alleles?

Accepted Answer

Dominant lethal alleles often cause death before reproductive age, preventing their transmission to offspring.

Question 2

A woman who is heterozygous for the X-linked gene for red-green color blindness (X	extsuperscript{N}X	extsuperscript{n}) marries a man with normal vision (X	extsuperscript{N}Y). What is the probability that their son will be color blind?

Accepted Answer

$$0.25$$

Question 3

Which of the following statements about X-inactivation in female mammals is correct?

Accepted Answer

X-inactivation results in the formation of Barr bodies, which are reactivated in ovarian cells for meiosis.

Question 4

In Morgan’s experiments with Drosophila, why did all F1 offspring from a cross between a white-eyed male and a red-eyed female have red eyes?

Accepted Answer

The red-eye allele is dominant and located on the X chromosome.

Question 5

Which equation represents the expected phenotypic ratio in the F2 generation for a dihybrid cross according to the law of independent assortment?

Accepted Answer

$$9:3:3:1$$

Question 6

A male with the genotype X	extsuperscript{n}Y for an X-linked recessive disorder and a female who is a carrier (X	extsuperscript{N}X	extsuperscript{n}) have children. What is the probability that a daughter will have the disorder?

Accepted Answer

$$0.25$$

Question 7

Which of the following best describes the chromosomal theory of inheritance?

Accepted Answer

Genes are located on chromosomes, and their behavior during meiosis explains Mendel’s laws.

Question 8

In the Z-W sex determination system, which of the following is true?

Accepted Answer

Males are ZZ and females are ZW.

Question 9

A geneticist observes a 1:1:1:1 phenotypic ratio in the F2 generation of a cross. Which process best explains this result?

Accepted Answer

Independent assortment of alleles on different chromosomes.

Question 10

Which of the following is a real-life example of a recessive lethal allele in humans?

Accepted Answer

Phenylketonuria (PKU), where individuals lack an enzyme to break down phenylalanine.

Question 11

Which of the following best explains why males are more likely to express X-linked recessive disorders?

Accepted Answer

Males have only one X chromosome and are hemizygous for X-linked genes.

Question 12

A tortoiseshell cat has patches of black and orange fur. Which genetic mechanism explains this phenotype?

Accepted Answer

Random X-inactivation in heterozygous females.

Question 13

Which of the following is NOT a mechanism of sex determination described in animals?

Accepted Answer

Mitochondrial inheritance system.

Question 14

If a gene is located on the Y chromosome, which of the following statements is true?

Accepted Answer

Only males can inherit and express Y-linked traits.

Question 15

Which of the following best describes the inheritance pattern of Duchenne muscular dystrophy?

Accepted Answer

It is an X-linked recessive disorder, primarily affecting males.

Question 16

A woman with normal vision (X	extsuperscript{N}X	extsuperscript{N}) and a man with red-green color blindness (X	extsuperscript{n}Y) have children. What is the expected phenotype of their daughters?

Accepted Answer

All daughters will be carriers but have normal vision.

Question 17

Which of the following is a consequence of aneuploidy in humans?

Accepted Answer

Down syndrome, caused by trisomy 21.

Question 18

Which of the following statements about Barr bodies is correct?

Accepted Answer

A Barr body is an inactivated X chromosome found in female somatic cells.

Question 19

Which of the following best explains why calico cats are almost always female?

Accepted Answer

The gene for coat color is X-linked, and random X-inactivation in heterozygous females produces the calico pattern.

Question 20

Which of the following is an example of the law of segregation?

Accepted Answer

Each gamete receives only one allele for a given gene during meiosis.

Chromosomal Genetics: The Chromosomal Basis of Inheritance and Sex-Linked Traits

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