Question 1

A cross between two heterozygous yellow mice (Aa) results in a phenotypic ratio of live offspring that is not 3:1. If the AA genotype produces agouti coat color, Aa produces yellow, and aa is lethal, what is the expected ratio of yellow to agouti among live offspring?

Accepted Answer

$$2:1$$\ 	ext{yellow:agouti}$

Question 2

In Morgan's experiments with Drosophila, the white-eyed trait appeared only in males in the F2 generation when a white-eyed male was crossed with a red-eyed female. What does this observation support?

Accepted Answer

The gene for eye color is located on the X chromosome.

Question 3

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 4

A new allele arises on the Y chromosome in Drosophila that reduces body size by half. Which offspring will inherit this allele from a male carrying it?

Accepted Answer

Only male offspring.

Question 5

Which process is responsible for the production of recombinant chromosomes during meiosis?

Accepted Answer

Crossing over between homologous chromosomes

Question 6

If two genes are located 12 map units apart on a chromosome, what is the expected recombination frequency between them?

Accepted Answer

$$12\%$$

Question 7

Which chromosomal abnormality is most likely to result from nondisjunction during meiosis II?

Accepted Answer

A zygote with three copies of a chromosome (trisomy)

Question 8

A child is born with cri du chat syndrome, which is caused by a specific chromosomal alteration. What is the nature of this alteration?

Accepted Answer

Deletion of a segment on chromosome 5

Question 9

Which of the following statements about polyploidy is correct?

Accepted Answer

Polyploidy results in organisms with more than two complete sets of chromosomes.

Question 10

Which enzyme is responsible for relieving the strain caused by unwinding of the DNA double helix during replication?

Accepted Answer

Topoisomerase

Question 11

During DNA replication, why is the lagging strand synthesized in short fragments?

Accepted Answer

DNA polymerase can only synthesize DNA in the 5' to 3' direction, away from the replication fork.

Question 12

Which of the following best describes the function of telomerase in germ cells?

Accepted Answer

It lengthens telomeres to prevent the loss of genetic information during replication.

Question 13

Which experimental evidence first demonstrated that DNA, and not protein, is the genetic material in viruses?

Accepted Answer

Hershey and Chase's bacteriophage experiment

Question 14

Which of the following is a direct result of X inactivation in female mammals?

Accepted Answer

One X chromosome in each cell is randomly inactivated, forming a Barr body.

Question 15

A woman with Turner syndrome has only one X chromosome (XO). Which of the following statements is true?

Accepted Answer

Turner syndrome is the only known viable human monosomy.

Question 16

Which of the following best describes the relationship between map units and recombination frequency?

Accepted Answer

One map unit equals a 1% recombination frequency.

Question 17

Which of the following is an example of genomic imprinting?

Accepted Answer

A gene is expressed only if inherited from the mother, but not from the father.

Question 18

Which of the following is true about the inheritance of mitochondrial DNA mutations?

Accepted Answer

They are inherited only from the mother.

Question 19

Which of the following best explains why DNA is packaged into chromatin in eukaryotic cells?

Accepted Answer

To fit the large amount of DNA into the nucleus and regulate gene expression

Question 20

Which base pairing in DNA is correct according to Chargaff's rules and the double helix structure?

Accepted Answer

A pairs with T, G pairs with C

Chromosomal and Molecular Basis of Inheritance: Study Notes

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