Q: Which formula correctly calculates the map distance between two genes?

Map Distance $$= \frac{\text{Number of recombinant offspring}}{\text{Total number of offspring}} \times 100$$

Question 1

Which of the following best describes Mendel's Law of Segregation?

Accepted Answer

Alleles are paired in diploid cells, and only one allele from each pair is transmitted to offspring in the gamete.

Question 2

In the absence of crossing over, what is the expected outcome for linked alleles during meiosis?

Accepted Answer

Linked alleles will segregate together, producing only parental types.

Question 3

A chiasma forms between loci A and B in 30% of tetrads during meiosis. What percent of gametes will be recombinant types?

Accepted Answer

15%

Question 4

Which formula correctly calculates the map distance between two genes?

Accepted Answer

Map Distance $$= \frac{	ext{Number of recombinant offspring}}{	ext{Total number of offspring}} 	imes 100$$

Question 5

If the map distance between loci B and C is 12 map units, what percent of gametes should be crossover types?

Accepted Answer

12%

Question 6

Which of the following statements about genetic recombination is correct?

Accepted Answer

Genetic recombination results from crossing over between homologous chromosomes.

Question 7

In a trihybrid test cross, which phenotypes are expected to occur most frequently?

Accepted Answer

Parental phenotypes

Question 8

What is the product rule for predicting the likelihood of a double crossover?

Accepted Answer

Multiply the probability of each single crossover event.

Question 9

Given the following data from a trihybrid cross: 411 gray body, red eyes, normal wings; 61 gray body, red eyes, vestigial wings; 2 gray body, purple eyes, normal wings; 30 gray body, purple eyes, vestigial wings; 28 black body, red eyes, normal wings; 1 black body, red eyes, vestigial wings; 60 black body, purple eyes, normal wings; 412 black body, purple eyes, vestigial wings. What is the total number of progeny?

Accepted Answer

1,005

Question 10

If the observed number of double crossovers is 3 and the expected number is 7.5, what is the coefficient of coincidence?

Accepted Answer

$$C = \frac{3}{7.5} = 0.4$$

Question 11

What does positive interference mean in genetic mapping?

Accepted Answer

The first crossover decreases the probability of a second crossover nearby.

Question 12

Which of the following is NOT a use of genetic maps?

Accepted Answer

Determining the protein structure of enzymes

Question 13

If the map distance between gene b and pr is 6.1 mu and between pr and vg is 12.3 mu, what is the map distance between b and vg?

Accepted Answer

$$6.1 + 12.3 = 18.4 mu$$

Question 14

Why does the observed number of recombinant offspring underestimate the map distance when genes are far apart?

Accepted Answer

Multiple crossovers can occur, restoring parental combinations.

Question 15

In a testcross involving two genes, what is the expected phenotypic ratio if the genes assort independently?

Accepted Answer

1:1:1:1

Question 16

Which scientist first created a chromosome linkage map?

Accepted Answer

Alfred Sturtevant

Question 17

What is the formula for interference (i) in genetic mapping?

Accepted Answer

$$i = 1 - C$$

Question 18

Which of the following best explains why parental phenotypes are most common in the offspring of crosses involving linked genes?

Accepted Answer

Linked genes tend to be transmitted together unless crossing over occurs.

Question 19

In a dihybrid cross involving linked genes, what is the maximum recombination frequency that can be observed?

Accepted Answer

50%

Chromosome Mapping and Linkage in Eukaryotes

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