Question 1

Which statement best explains the Chromosomal Theory of Inheritance?

Accepted Answer

Genes are located on chromosomes, and the behavior of chromosomes during meiosis accounts for inheritance patterns described by Mendel.

Question 2

Why is Drosophila melanogaster considered a model organism for genetic studies?

Accepted Answer

It breeds at a high rate, has a short generation time, and only four pairs of chromosomes.

Question 3

In Drosophila, red eyes (w+) are dominant to white eyes (w). If a female with genotype $$w^+w is $$crossed with a male with genotype $$w^+Y$$, what is the expected phenotypic ratio in the offspring?

Accepted Answer

All offspring will have red eyes.

Question 4

Which of the following best describes why only male Drosophila had white eyes in Morgan's experiments?

Accepted Answer

The white-eye allele is located on the X chromosome and is recessive; males only have one X chromosome.

Question 5

A woman heterozygous for color blindness ($$X^CX^c) $$has a child with a man who is colorblind ($$X^cY). $$What is the probability that their offspring will be a colorblind female?

Accepted Answer

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

Question 6

Which of the following conditions is caused by an extra copy of chromosome 21?

Accepted Answer

Down syndrome

Question 7

What is the effect of X chromosome inactivation in female mammals?

Accepted Answer

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

Question 8

Which equation represents the probability of a female offspring being a carrier for color blindness when a homozygous dominant woman ($$X^CX^C) $$mates with a colorblind man ($$X^cY$$)?

Accepted Answer

$$P = \frac{1}{2}$$

Question 9

Which syndrome is associated with the karyotype $$47, XXY$$?

Accepted Answer

Klinefelter syndrome

Question 10

What is the most likely outcome of a full chromosome loss or gain (aneuploidy) in humans?

Accepted Answer

Aneuploidy almost always results in death of the organism.

Question 11

Which of the following best explains why calico cats are almost always female?

Accepted Answer

X chromosome inactivation leads to mosaic expression of coat color genes, which requires two X chromosomes.

Question 12

If nondisjunction occurs during meiosis I in a human female, what is the possible chromosomal outcome in the offspring?

Accepted Answer

Some offspring may have an extra chromosome (trisomy) or be missing a chromosome (monosomy).

Question 13

Which equation best represents the relationship between maternal age and the risk of Down syndrome in live births?

Accepted Answer

$$Risk = a \cdot e$$^{b \cdot Age}$$

Question 14

Which of the following is a non-lethal aneuploidy compatible with life due to the unique nature of the X chromosome?

Accepted Answer

Turner syndrome (XO)

Question 15

A male with genotype $$X^cY ($$colorblind) mates with a female with genotype $$X^CX^c ($$carrier). What is the probability that their offspring will be a carrier female?

Accepted Answer

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

Question 16

Which of the following best describes the formation of a Barr body?

Accepted Answer

One X chromosome in each female cell is randomly inactivated and condensed into a Barr body.

Question 17

Which syndrome is associated with the karyotype $$45, XO$$?

Accepted Answer

Turner syndrome

Question 18

Which of the following is NOT a recessive allele that may reside on the X chromosome?

Accepted Answer

Cystic fibrosis

Question 19

If a female cat has both black and orange fur, what genetic mechanism explains this phenotype?

Accepted Answer

Random inactivation of one X chromosome in each cell, leading to mosaic expression of coat color genes.

Chromosomal Theory of Inheritance and Human Chromosomal Disorders

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