Question 1

Which of the following best explains why white-eyed male fruit flies appeared in the F2 generation of Morgan's classic cross, but not in the F1 generation?

Accepted Answer

The white-eye allele is recessive and X-linked, so males only need one copy to express the trait.

Question 2

According to Mendel’s Law of Segregation, what happens to alleles during gamete formation?

Accepted Answer

The two alleles for a heritable character separate and end up in different gametes.

Question 3

A woman who is heterozygous for the X-linked recessive allele for color blindness (X^N X^n) marries a man with normal vision (X^N Y). What is the probability that their son will be color blind?

Accepted Answer

$$\frac{1}{2}$$

Question 4

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

Accepted Answer

The inactivated X chromosome forms a Barr body.

Question 5

If two genes are located very close together on the same chromosome, which of the following is most likely true?

Accepted Answer

They are likely to be inherited together due to genetic linkage.

Question 6

A geneticist observes that two genes have a recombination frequency of 17%. What does this indicate about their physical relationship on the chromosome?

Accepted Answer

They are 17 map units apart on the chromosome.

Question 7

Which chromosomal abnormality is most likely to result in Down syndrome?

Accepted Answer

Trisomy 21

Question 8

A plant is found to have three complete sets of chromosomes (3n). What is this condition called?

Accepted Answer

Polyploidy

Question 9

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

Accepted Answer

It is inherited only from the mother.

Question 10

A male with Klinefelter syndrome has which of the following karyotypes?

Accepted Answer

$$XXY$$

Question 11

Which of the following chromosomal changes involves a segment of a chromosome being reversed end to end?

Accepted Answer

Inversion

Question 12

A woman who is a carrier for hemophilia (an X-linked recessive disorder) has children with a man who does not have hemophilia. What is the probability that their daughter will have hemophilia?

Accepted Answer

$$\frac{1}{4} ($$only if the daughter inherits the affected X from both parents, but the father is not affected, so the answer is 0)

Question 13

Which of the following is a real-life example of a human disorder caused by a deletion of a chromosomal segment?

Accepted Answer

Cri du chat syndrome

Question 14

In a testcross between a dihybrid fruit fly (b+ vg+/b vg) and a double recessive fly (b vg/b vg), most offspring have parental phenotypes, but some have recombinant phenotypes. What process explains the appearance of recombinant phenotypes?

Accepted Answer

Crossing over during meiosis

Question 15

Which of the following best explains why X-linked recessive disorders are more common in males than in females?

Accepted Answer

Males have only one X chromosome, so a single recessive allele will cause the disorder.

Question 16

A geneticist is mapping two genes and finds a recombination frequency of 2%. What does this suggest about the physical distance between the two genes?

Accepted Answer

They are very close together on the same chromosome.

Question 17

Which of the following is NOT a possible result of nondisjunction during meiosis?

Accepted Answer

A gamete with only autosomes and no sex chromosomes

Question 18

Which of the following statements about linked genes is correct?

Accepted Answer

Linked genes tend to be inherited together because they are located near each other on the same chromosome.

Question 19

A woman with Turner syndrome has which of the following karyotypes?

Accepted Answer

$$X0$$

Question 20

Which of the following best describes the chromosomal basis for the tortoiseshell coloration in female cats?

Accepted Answer

It results from random X chromosome inactivation in heterozygous females.

Chromosomal Basis of Inheritance and Exceptions to Mendelian Genetics

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