Question 1

A cross between two heterozygous Aa mice at the agouti locus results in offspring with agouti and yellow coats, but aa homozygotes die early in development. What is the expected phenotypic ratio of live mice from this cross?

Accepted Answer

2:1 agouti:yellow

Question 2

Which of the following statements 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 3

In Drosophila, a new allele arises on the Y chromosome that reduces body size by half. Which statement is accurate regarding its inheritance?

Accepted Answer

This allele is passed to all male but no female offspring of a male with the allele.

Question 4

Which chromosomal system of sex determination is found in birds?

Accepted Answer

Z-W system

Question 5

A female mammal is heterozygous for a gene on the X chromosome. What is the expected result in her somatic cells due to X inactivation?

Accepted Answer

She will be a mosaic for the gene, with some cells expressing one allele and some the other.

Question 6

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

Accepted Answer

Crossing over

Question 7

If two genes are located 20 map units apart on a chromosome, what is the expected recombination frequency between them?

Accepted Answer

$$0.2$$

Question 8

Which chromosomal abnormality is most commonly associated with Down syndrome?

Accepted Answer

Trisomy 21

Question 9

A child is born with cri du chat syndrome. Which chromosomal event caused this disorder?

Accepted Answer

Deletion of chromosome 5

Question 10

Which of the following is true about polyploidy?

Accepted Answer

Polyploid organisms have more than two complete sets of chromosomes.

Question 11

Which enzyme is responsible for relieving strain ahead of the replication fork during DNA replication?

Accepted Answer

Topoisomerase

Question 12

What is the function of telomerase in germ cells?

Accepted Answer

It lengthens telomeres to maintain chromosome integrity.

Question 13

Which of the following best describes the semiconservative model of DNA replication?

Accepted Answer

Each daughter DNA molecule consists of one parental strand and one newly synthesized strand.

Question 14

Which of the following is a direct result of nondisjunction during meiosis?

Accepted Answer

Some gametes have an extra chromosome, while others lack one.

Question 15

Which of the following inheritance patterns is an exception to Mendelian genetics and involves the silencing of certain genes depending on the parent of origin?

Accepted Answer

Genomic imprinting

Question 16

Which of the following statements about mitochondrial DNA inheritance is correct?

Accepted Answer

Mitochondrial DNA is inherited only from the mother.

Question 17

Which of the following best explains why the frequency of Down syndrome increases with maternal age?

Accepted Answer

Nondisjunction events during meiosis become more common as maternal age increases.

Question 18

Which of the following is true about the packaging of DNA in eukaryotic cells?

Accepted Answer

DNA is packaged with proteins called histones to form chromatin.

Question 19

Which base pairing in DNA results in a uniform width of the double helix?

Accepted Answer

Purine with pyrimidine

Question 20

A diploid animal is heterozygous at two loci, H and T. Which of the following gamete genotypes could this animal produce?

Accepted Answer

HT

Chromosomal and Molecular Basis of Inheritance

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