Question 1

According to the chromosome theory of inheritance, what is the relationship between genes and chromosomes?

Accepted Answer

Genes are located on chromosomes, and each chromosome carries many genes at specific loci.

Question 2

During meiosis, what process ensures that alleles segregate into different gametes?

Accepted Answer

Separation of homologous chromosomes during Anaphase I

Question 3

Which of the following best explains why sex-linked diseases are more common in males?

Accepted Answer

Males are hemizygous for the X chromosome, so a single recessive allele will cause the disease.

Question 4

A female carrier for hemophilia (XDXd) marries a male with normal blood clotting (XDY). What fraction of their male children will have hemophilia?

Accepted Answer

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

Question 5

What is the probability that a human male will inherit an X-linked recessive allele from his father?

Accepted Answer

0%

Question 6

A genetic defect in humans results in the absence of sweat glands in the skin. In women, this defect is expressed in patches. What is the most likely explanation for this pattern?

Accepted Answer

X chromosome inactivation

Question 7

If two genes are located far apart on the same chromosome, what is their expected recombination frequency?

Accepted Answer

$$50\%$$

Question 8

In a testcross of F1 dihybrid flies, if the percentages of parental and recombinant offspring are about the same, what does this indicate about the two genes?

Accepted Answer

The genes are unlinked.

Question 9

In cosmos plants, purple stem (A) is dominant to green stem (a), and short petals (B) is dominant to long petals (b). If AaBb plants are testcrossed with aabb plants and the genes are unlinked, what is the expected phenotypic ratio among the offspring?

Accepted Answer

1:1:1:1

Question 10

If 900 offspring are produced from a testcross of AaBb × aabb and the genes are unlinked, how many offspring of each phenotype are expected?

Accepted Answer

$$225$$

Question 11

Which chromosomal alteration is associated with Huntington’s disease due to repeated DNA sequences?

Accepted Answer

Duplication

Question 12

A child is born with a missing chromosome, resulting in Turner’s syndrome. What is the chromosomal notation for this condition?

Accepted Answer

$$XO$$

Question 13

Which chromosomal abnormality is most commonly associated with Down syndrome?

Accepted Answer

Trisomy (2n+1)

Question 14

Which event during meiosis can lead to aneuploidy?

Accepted Answer

Nondisjunction during Anaphase I or II

Question 15

Which chromosomal alteration involves a segment of a chromosome being oriented in the reverse direction?

Accepted Answer

Inversion

Question 16

A reciprocal translocation between chromosomes 9 and 22 is associated with which human disorder?

Accepted Answer

Chronic myelogenous leukemia

Question 17

Which of the following is true about X chromosome inactivation in female mammals?

Accepted Answer

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

Question 18

Which chromosomal alteration is most likely to cause infertility due to improper pairing during meiosis?

Accepted Answer

Inversion

Question 19

If a gene is located on the X chromosome and a male inherits a disease allele, what is his genotype?

Accepted Answer

$$XdY$$

Question 20

Which of the following best describes the outcome of crossing over between linked genes?

Accepted Answer

It increases genetic diversity by producing recombinant chromosomes.

The Chromosomal Basis of Inheritance: Study Notes

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