Question 1

A cross between two heterozygous four-o'clock plants (Rr x Rr) produces offspring with red, pink, and white flowers. Which type of inheritance does this illustrate, and what is the expected phenotypic ratio among the offspring?

Accepted Answer

Incomplete dominance; 1:2:1

Question 2

In cats, the Manx phenotype (tailless) is caused by a dominant allele (M) that is lethal in the homozygous state (MM). If two Manx cats are crossed, what proportion of the surviving offspring are expected to be Manx?

Accepted Answer

$\frac{1}{2}$

Question 3

A woman with blood type AB and a man with blood type O have children. Which blood types are possible among their children?

Accepted Answer

A and B only

Question 4

Which of the following best describes the molecular basis of dominance in the pea plant flower color example?

Accepted Answer

The presence of any functional enzyme from either allele is sufficient to produce the purple pigment.

Question 5

In a dihybrid cross involving two independently assorting genes (AaBb x AaBb), what is the expected phenotypic ratio in the F2 generation?

Accepted Answer

$9:3:3:1$

Question 6

A geneticist performs a complementation test by crossing two white-flowered mutants. All F1 offspring have blue flowers. What does this result indicate?

Accepted Answer

The mutations are in different genes.

Question 7

A woman who is a carrier for hemophilia (an X-linked recessive disorder) marries a man without hemophilia. What is the probability that their son will have hemophilia?

Accepted Answer

$\frac{1}{2}$

Question 8

In corn snakes, skin coloration is determined by two genes in distinct pathways: one for orange pigment (O) and one for black pigment (B). If a snake is homozygous recessive for both genes (oo;bb), what will its phenotype be?

Accepted Answer

Albino

Question 9

Which of the following best explains why the F2 generation from a dihybrid cross of two genes in the same pathway (with recessive epistasis) produces a 9:3:4 phenotypic ratio?

Accepted Answer

One gene masks the effect of the other when homozygous recessive.

Question 10

A man with X-linked color blindness (recessive) marries a woman who is homozygous for normal vision. What is the expected outcome for their children?

Accepted Answer

All sons will have normal vision, all daughters will be carriers.

Question 11

Which of the following is a key feature of X-linked dominant inheritance as observed in pedigrees?

Accepted Answer

Affected mothers pass the trait to half of their sons and half of their daughters.

Question 12

If two genes are duplicated such that either gene can produce the same phenotype, what is the expected phenotypic ratio in the F2 generation from a dihybrid cross?

Accepted Answer

$15:1$

Question 13

A couple, both with blood type AB, are planning to have children. What is the probability that their child will have blood type O?

Accepted Answer

$0$

Question 14

Which of the following scenarios would most likely result in a modified 9:7 phenotypic ratio in the F2 generation?

Accepted Answer

Two genes in the same pathway, both required for the phenotype

Question 15

A researcher crosses two pure-breeding white-flowered plants and obtains all blue-flowered F1 offspring. When the F1 are self-crossed, the F2 generation shows a 9:3:4 ratio of blue:magenta:white. What genetic phenomenon does this illustrate?

Accepted Answer

Recessive epistasis

Question 16

Which of the following statements about Mendel's Law of Independent Assortment is correct?

Accepted Answer

It states that alleles of different genes assort independently during gamete formation.

Question 17

A woman with genotype $X^A X^a$ (where $A$ is normal and $a$ is a recessive X-linked disorder) has children with a man with genotype $X^a Y$. What is the probability that a daughter will be affected by the disorder?

Accepted Answer

$\frac{1}{4}$

Question 18

Which of the following best describes the outcome of a complementation test where two mutants fail to complement each other?

Accepted Answer

The mutations are in the same gene.

Question 19

In a cross between two heterozygous individuals for two genes (AaBb x AaBb), what is the probability of obtaining an offspring that is homozygous recessive for both genes?

Accepted Answer

$\frac{1}{16}$

Extensions of Mendelian Genetics: Chapter 4 Study Notes

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