Question 1

Which of the following best describes the phenomenon of genetic linkage?

Accepted Answer

Genes located close together on the same chromosome tend to be inherited together.

Question 2

A testcross between AaBb and aabb plants yields the following progeny: 126 AaBb, 28 Aabb, 32 aaBb, 114 aabb. What is the map distance between genes A and B? Use the formula $$	ext{Map\ units} = \frac{	ext{Number\ of\ recombinants}}{	ext{Total\ offspring}} 	imes 100.$$

Accepted Answer

$$20\ 	ext{map\ units}$$

Question 3

Which of the following statements about crossing over is correct?

Accepted Answer

Crossing over occurs between nonsister chromatids during meiosis I.

Question 4

If two genes are 60 map units apart, what percentage of recombinant gametes would you expect to observe?

Accepted Answer

$$50\%$$

Question 5

In a three-point testcross, the noncrossover phenotypes occur in the greatest proportion of offspring. What does this indicate about the arrangement of genes?

Accepted Answer

The noncrossover phenotypes represent the parental arrangement of alleles.

Question 6

Which of the following is a direct consequence of positive interference during crossing over?

Accepted Answer

Fewer double crossovers than expected are observed.

Question 7

A linkage group is best defined as:

Accepted Answer

All of the genes located on the same chromosome.

Question 8

Which experimental approach allows researchers to assign human genes to specific chromosomes by correlating gene products with the presence or absence of chromosomes in hybrid cell lines?

Accepted Answer

Synteny testing

Question 9

If the recombination frequency between gene y and gene w is $$0.5\%$$, between w and m is $$34.5\%$$, and between y and m is $$35.4\%$$, what is the most likely gene order?

Accepted Answer

y - w - m

Question 10

Which of the following best explains why the maximum observable recombination frequency between two genes is $$50\%$$?

Accepted Answer

Because independent assortment produces equal numbers of parental and recombinant gametes.

Question 11

In a three-point cross, the expected frequency of double crossovers between genes A and C, given that the crossover probability between A and B is $$10\%$$ and between B and C is $$10\%$$, is:

Accepted Answer

$$0.01$$

Question 12

Which of the following is NOT a reason why genetic map distances are not strictly additive?

Accepted Answer

Physical distance between genes is always equal to map distance

Question 13

Which of the following statements about somatic cell hybridization is correct?

Accepted Answer

It allows assignment of human genes to specific chromosomes.

Question 14

Which of the following best describes the relationship between map units and recombination frequency?

Accepted Answer

1 map unit equals 1 percent recombination.

Question 15

Which of the following is a direct application of the coefficient of coincidence in genetic mapping?

Accepted Answer

To quantify the disparity between observed and expected double crossovers.

Question 16

Which of the following is true regarding the mapping of human genes using lod score analysis?

Accepted Answer

It uses probability calculations based on pedigree data.

Question 17

Which of the following is a consequence of multiple crossovers between two genes that are far apart on a chromosome?

Accepted Answer

The observed recombination frequency underestimates the actual number of crossovers.

Question 18

Which of the following best describes the outcome of a testcross between AaBb and aabb when the genes are unlinked?

Accepted Answer

The offspring will be produced in a 1:1:1:1 ratio.

Question 19

The genes A, B, and C occur in that order in fruit flies. A is 10 map units from B, and B is 20 map units from C. How far is A from C?

Accepted Answer

$$30\ 	ext{map\ units}$$

Linkage and Chromosome Mapping in Eukaryotes: Study Guide

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