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 heterozygous tall pea plant (Tt) and a dwarf plant (tt), what is the expected ratio of tall to dwarf offspring?

Accepted Answer

$$1:1$$

Question 5

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

Accepted Answer

$$1/4$$

Question 6

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 7

A dihybrid plant is self-fertilized and the F2 generation consists of 860 tall plants with purple flowers, 285 dwarf, purple plants, 340 tall, pink plants, and 115 dwarf, pink plants. The data fit a $$9:3:3:1$$ ratio. If the critical chi-square for two degrees of freedom is $$5.991$$, what should you conclude if your calculated chi-square is less than this value?

Accepted Answer

Accept your hypothesis.

Question 8

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 9

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 10

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

Accepted Answer

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

Question 11

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 12

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

Accepted Answer

Affected males yield all affected daughters.

Question 13

In the cell division figure below (showing four chromosomes aligned at the metaphase plate, 2n=4), 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 this organism be in humans?

Accepted Answer

Male human being

Question 15

A pedigree shows a trait that is present in every generation and affected males have all affected daughters but no affected sons. What is the most likely mode of inheritance?

Accepted Answer

X-linked dominant

Question 16

If a dihybrid plant (AaBb) is testcrossed, what is the expected phenotypic ratio of the offspring?

Accepted Answer

$$1:1:1:1$$

Question 17

In a pedigree, what is the chance that individual III-2 is a heterozygous carrier if both parents are heterozygous and the trait is autosomal recessive?

Accepted Answer

$$50\%$$

Question 18

Huntington's disease is an autosomal dominant trait. If an affected individual has three children with a normal partner, what is the probability that exactly two of the three children will have the disorder?

Accepted Answer

$$3/8$$

Question 19

Which of the following best describes expressivity in genetics?

Accepted Answer

The degree to which a genotype is expressed in an individual.

Question 20

A pedigree shows a trait that never passes from father to son and affected males are born to carrier mothers. What is the most likely mode of inheritance?

Accepted Answer

X-linked recessive

Genetics Exam Study Guide: Pedigree Analysis, Mendelian Inheritance, and Probability

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