Question 1

During meiosis, if a gamete is produced containing two Y chromosomes, at which division did the nondisjunction event most likely occur?

Accepted Answer

Second division

Question 2

Two homologous chromosomes fail to pair during prophase I of meiosis. Which outcome is most likely?

Accepted Answer

Both crossing over is eliminated and high probability of nondisjunction

Question 3

A couple has 7 children. What is the probability that they have exactly 3 girls and 4 boys? Use the binomial probability formula $$P = \binom{n}{k} p^k (1-p$$)^{n-k}$$ with p = 0.5$.

Accepted Answer

$$\frac{35}{128}$$

Question 4

If a couple has 7 children, what is the probability that they have 3 or more girls? (Assume each child is equally likely to be a girl or boy.)

Accepted Answer

$$\frac{119}{128}$$

Question 5

In a cross AaBbccddEe x aaBbCcDdee, what is the probability of obtaining an individual that expresses the recessive phenotype for all 5 loci?

Accepted Answer

$$\frac{1}{128}$$

Question 6

The ability to taste phenylthiourea (PTC) is dominant. If both parents are heterozygous (Tt), what is the probability of having a family of 4 with exactly two tasters and two non-tasters? Use the binomial formula $$P = \binom{4}{2} (0.75)^2$ (0.25)^2$.

Accepted Answer

$$\frac{54}{256}$$

Question 7

In peas, tall is dominant to short, and round is dominant to wrinkled. A plant heterozygous for both loci is crossed to an unknown plant. The progeny are: 598 tall round, 210 tall wrinkled, 602 short round, 198 short wrinkled. What was the phenotype of the unknown plant?

Accepted Answer

Short round

Question 8

A tall round pea plant, when self-pollinated, produces a 9:3:3:1 ratio of tall round: tall wrinkled: short round: short wrinkled. What ratio would result if this plant were crossed to a homozygous short wrinkled plant?

Accepted Answer

1:1:1:1 ratio of tall round: tall wrinkled: short round: short wrinkled

Question 9

In Drosophila, yellow body (y) is sex-linked and recessive, brown eyes (bw) is autosomal and recessive. A yellow brown male is crossed to a homozygous wild-type female, producing F1 wild-type flies. The F1 are inbred to form F2. What is the expected frequency of yellow (but not brown) males in the F2?

Accepted Answer

$$\frac{1}{16}$$

Question 10

Cystic fibrosis is inherited as an autosomal recessive. Two unaffected parents have two children with cystic fibrosis and three without. What is the probability that their next child will have cystic fibrosis?

Accepted Answer

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

Question 11

For the family in the previous question, what is the probability that a given unaffected child is heterozygous for the cystic fibrosis allele?

Accepted Answer

$$\frac{2}{3}$$

Question 12

Which of the following best describes the principle of segregation and the principle of independent assortment, and where each occurs in meiosis?

Accepted Answer

The principle of segregation is demonstrated in Anaphase I; the principle of independent assortment in Metaphase I.

Question 13

Mendel's law of independent assortment is violated by which of the following?

Accepted Answer

Linkage

Question 14

In Jimsonweed, purple flowers are dominant to white. When a particular purple-flowered Jimsonweed is self-fertilized, there are 28 purple-flowered and 10 white-flowered progeny. What proportion of the purple-flowered progeny will breed true?

Accepted Answer

$$\frac{1}{3}$$

Question 15

The cross of an uncertain genotype with a homozygous recessive genotype at the same locus is called a:

Accepted Answer

Testcross

Question 16

Which year (+/- 20 years) did Mendel publish his work on genetics?

Accepted Answer

1850

Question 17

A three-generation pedigree for a human trait shows that Y-linked inheritance can be excluded. Assuming complete penetrance and full expressivity, what is the most likely mode of inheritance?

Accepted Answer

Autosomal dominant

Question 18

If two homologous chromosomes fail to pair during prophase I, which genetic law is most likely to be affected?

Accepted Answer

Law of independent assortment

Question 19

A dihybrid cross produces an F1 generation with a 12:3:1 ratio. If an F1 individual is test-crossed, what is the expected ratio of phenotypes in the progeny?

Accepted Answer

1:1:1:1

Question 20

In a real-world scenario, a genetic counselor is asked about the risk of cystic fibrosis in a family where both parents are carriers. What is the probability that a child will be unaffected and not a carrier?

Accepted Answer

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

Genetics 2450: Sample Exam Study Guide

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