Question 1

Which of the following best describes penetrance in genetics?

Accepted Answer

The proportion of individuals with a particular genotype that actually displays the associated phenotype.

Question 2

A pedigree shows a trait that appears in every generation and affects both males and females equally. What is the most likely mode of inheritance?

Accepted Answer

Autosomal dominant

Question 3

A dihybrid cross AaBb x AaBb is performed. Assuming independent assortment, what is the expected phenotypic ratio among the offspring?

Accepted Answer

$$9:3:3:1$$

Question 4

In a testcross between a dihybrid (AaBb) and a double recessive (aabb), what is the expected phenotypic ratio if the genes assort independently?

Accepted Answer

$$1:1:1:1$$

Question 5

A woman with normal vision whose father was colorblind has children with a man with normal color vision. Red-green color blindness is X-linked recessive. What is the probability that their first child will be colorblind?

Accepted Answer

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

Question 6

A dihybrid plant is self-fertilized and the F2 generation consists of 860 tall purple, 285 dwarf purple, 340 tall pink, and 115 dwarf pink plants. The critical chi-square for two degrees of freedom is 5.991. Should you accept or reject the hypothesis that the observed ratio fits a $$9:3:3:1$$ ratio?

Accepted Answer

Accept your hypothesis

Question 7

Which of the following is true about X-linked recessive inheritance?

Accepted Answer

Affected males are usually born to carrier mothers

Question 8

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

Accepted Answer

Autosomal recessive

Question 9

A woman whose husband worked at the Chernobyl nuclear reactor gives birth to a hemophilic son. Which is the most likely genetic explanation?

Accepted Answer

She should not blame the accident because she carried the hemophilia allele.

Question 10

A dihybrid (AaBb) lab mouse is testcrossed. What is the probability that the first three offspring are dihybrid females?

Accepted Answer

$$(1/8)^3 = 0.002$

Question 11

Which of the following best explains why Mendel's work was not appreciated until 1900?

Accepted Answer

There was no known physical basis for Mendel's 'gene' concept at the time.

Question 12

A pedigree shows a trait that is never passed from father to son, but affected males have affected daughters. What is the most likely mode of inheritance?

Accepted Answer

X-linked dominant

Question 13

A cell is shown with four chromosomes aligned at the metaphase plate, each consisting of two sister chromatids. What is the stage and ploidy?

Accepted Answer

Metaphase I of meiosis, $$2n = 4$$

Question 14

A diploid organism has an XXY sex chromosome complement. What would be the expected phenotype in humans?

Accepted Answer

Male human being

Question 15

In a cross between a pure-breeding green plant with full pods (FFyy) and a pure-breeding yellow plant with constricted pods (ffYY), what is the expected genotype of a yellow plant with constricted pods?

Accepted Answer

ffyy

Question 16

In the pedigree below, what is the probability that individual III-2 is a heterozygous carrier for an autosomal recessive trait?

Accepted Answer

50%

Question 17

Huntington's disease is an autosomal dominant trait. If individual IV-2 has three children with a normal man, what is the probability that exactly two of the three children would have the disorder?

Accepted Answer

$$3/8$$

Question 18

A male fruit fly and a female fruit fly are heterozygous for detached wings (det). What is the probability that of their first ten offspring, any five will be females with detached wings?

Accepted Answer

$$(10!/(5!5!))(1/8)^5$(3/8)^5$

Question 19

Barring new mutation, and assuming complete penetrance and single-locus inheritance, what are possible modes of inheritance for a trait that appears only in males and skips generations?

Accepted Answer

X-linked recessive

Question 20

A pedigree shows a trait that appears in every generation and is passed from father to all sons. What is the most likely mode of inheritance?

Accepted Answer

Y-linked

Genetics Exam Study Guide: Pedigree Analysis, Mendelian Genetics, Probability, and Cell Division

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