Question 1

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

Accepted Answer

Males only need one copy of the recessive allele on their single X chromosome to express the disorder.

Question 2

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

Accepted Answer

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

Question 3

Which of the following statements about linked genes is correct?

Accepted Answer

Linked genes are located on the same chromosome and tend to be inherited together, but can be separated by crossing over.

Question 4

A geneticist observes a recombination frequency of 12% between two genes in fruit flies. What is the distance between these genes on a linkage map?

Accepted Answer

$$12$$ map units

Question 5

Which chromosomal alteration is correctly matched with its description?

Accepted Answer

Inversion: a segment of a chromosome is reversed within the chromosome

Question 6

A child is born with Down syndrome. Which of the following best describes the chromosomal basis of this condition?

Accepted Answer

The child has three copies of chromosome 21 due to nondisjunction during meiosis.

Question 7

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 8

A woman with mitochondrial myopathy is concerned about passing the disorder to her children. Which statement best explains the inheritance pattern of this disease?

Accepted Answer

Mitochondrial genes are inherited only from the mother, so all her children are at risk.

Question 9

If a female mammal is heterozygous for an X-linked gene, what is the expected result in her somatic cells due to X inactivation?

Accepted Answer

Some cells will express the maternal allele and others the paternal allele, resulting in a mosaic pattern.

Question 10

Which of the following best describes the outcome of nondisjunction during meiosis II in humans?

Accepted Answer

Half of the gametes will have an abnormal number of chromosomes.

Question 11

A male with Klinefelter syndrome has the following sex chromosome composition:

Accepted Answer

XXY

Question 12

Which process is responsible for producing recombinant chromosomes in linked genes?

Accepted Answer

Crossing over during prophase I of meiosis

Question 13

A plant is triploid ($$3n). $$Which of the following statements is true about its chromosome number?

Accepted Answer

It has three complete sets of chromosomes.

Question 14

Which of the following is a likely consequence of a reciprocal translocation between two nonhomologous chromosomes in a human somatic cell?

Accepted Answer

It may result in certain cancers, such as chronic myelogenous leukemia (CML).

Question 15

If two genes are 50 map units apart on the same chromosome, what is the expected recombination frequency between them?

Accepted Answer

$$50\%$$

Question 16

Which of the following best describes the function of the SRY gene in mammals?

Accepted Answer

It triggers the development of testes in embryos.

Question 17

A woman with genotype X	extsuperscript{A}X	extsuperscript{a} (where 'a' is a recessive allele for hemophilia) has a child with a man with genotype X	extsuperscript{A}Y. What is the probability that their daughter will have hemophilia?

Accepted Answer

$$\frac{1}{4}$$

Question 18

Which of the following is true about the inheritance of extranuclear genes?

Accepted Answer

They are inherited only from the mother because the zygote's cytoplasm comes from the egg.

Question 19

Which of the following best explains why polyploidy is more common in plants than in animals?

Accepted Answer

Plants tolerate extra sets of chromosomes better than animals do.

Question 20

A female cat is heterozygous for an X-linked gene that determines fur color. Due to X inactivation, what is the expected phenotype?

Accepted Answer

She will have patches of both fur colors, showing a mosaic pattern.

The Chromosomal Basis of Inheritance

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