Question 1

In mammals, which chromosome combination determines a biological male, and what gene is primarily responsible for initiating male development?

Accepted Answer

XY; SRY gene

Question 2

A grasshopper has an XO sex determination system. What is the chromosomal composition of a male grasshopper?

Accepted Answer

XO

Question 3

In Drosophila, the X:A ratio determines sex. What would be the expected sex of a fly with two X chromosomes and two sets of autosomes ($$X:A = 1.0$$)?

Accepted Answer

Female

Question 4

A human with the karyotype XXY is phenotypically:

Accepted Answer

Male with Klinefelter syndrome

Question 5

Which of the following best describes codominance?

Accepted Answer

Both alleles are expressed equally in the phenotype.

Question 6

A cross between two yellow mice (Yy × Yy) produces offspring in a 2:1 ratio of yellow to gray. What is the most likely explanation for this ratio?

Accepted Answer

Lethal allele

Question 7

Which genotype(s) result in blood type AB in humans?

Accepted Answer

$$I^A I^B$$

Question 8

In a dihybrid cross involving two genes with complete dominance, what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$$9:3:3:1$$

Question 9

Which of the following is an example of recessive epistasis?

Accepted Answer

Coat color in mice where cc genotype results in albino regardless of B gene

Question 10

A woman is heterozygous for an X-linked recessive trait. What is the probability that her son will express the trait?

Accepted Answer

$$0.5$$

Question 11

Which phenomenon explains why female mammals are genetic mosaics for X-linked genes?

Accepted Answer

X-chromosome inactivation (Lyon hypothesis)

Question 12

A pedigree shows a trait that appears more frequently in males and skips generations. What is the most likely mode of inheritance?

Accepted Answer

X-linked recessive

Question 13

Which of the following best describes penetrance?

Accepted Answer

The proportion of individuals with a specific genotype who express the expected phenotype

Question 14

In the four-o’clock plant, variegated leaf color is inherited through the cytoplasm. If a variegated female is crossed with a green male, what will be the phenotype of the offspring?

Accepted Answer

All variegated

Question 15

Which of the following is an example of a multifactorial (complex) characteristic?

Accepted Answer

Human height

Question 16

A Himalayan rabbit has dark fur on its ears and feet due to a temperature-sensitive allele. What does this illustrate?

Accepted Answer

Environmental effect on phenotype

Question 17

Which of the following is true about genomic imprinting?

Accepted Answer

It involves epigenetic silencing of genes depending on the parent of origin

Question 18

In a cross between two heterozygotes for two genes showing duplicate dominant epistasis, what is the expected F2 phenotypic ratio?

Accepted Answer

$$15:1$$

Question 19

Pattern baldness in humans is an example of which type of inheritance?

Accepted Answer

Sex-influenced inheritance

Question 20

A snail’s shell coiling direction is determined by the genotype of its mother, not its own genotype. This is an example of:

Accepted Answer

Genetic maternal effect

Extensions of Mendelian Inheritance: Sex Determination, Sex-linked Inheritance, and Gene Interactions

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