Q: A testcross between a dihybrid fly (BbVv) and a double recessive fly (bbvv) yields the following offspring: 965 wild type, 944 double mutant, 186 gray body with vestigial wings, and 185 black body with normal wings. What is the recombination frequency between the genes?

$$\frac{186 + 185}{965 + 944 + 186 + 185} \times 100 = 27\%$$

Question 1

Which of the following best explains why the number of genes in a cell is much greater than the number of chromosomes?

Accepted Answer

Each chromosome contains hundreds or thousands of genes.

Question 2

In Morgan’s experiments with Drosophila, what was the significance of the observation that body color and wing size were usually inherited together?

Accepted Answer

The genes for these traits are linked and located on the same chromosome.

Question 3

If two genes are located far apart on the same chromosome, what is the expected effect on their recombination frequency?

Accepted Answer

The recombination frequency will be high, approaching 50%.

Question 4

A testcross between a dihybrid fly (BbVv) and a double recessive fly (bbvv) yields the following offspring: 965 wild type, 944 double mutant, 186 gray body with vestigial wings, and 185 black body with normal wings. What is the recombination frequency between the genes?

Accepted Answer

$$\frac{186 + 185}{965 + 944 + 186 + 185} 	imes 100 = 27\%$$

Question 5

Which of the following statements about linked genes is correct?

Accepted Answer

Linked genes are located on the same chromosome and tend to be inherited together.

Question 6

What is the purpose of a chi-square ($$\$$chi^2$$) test in genetic experiments?

Accepted Answer

To compare observed and expected data to test a genetic hypothesis.

Question 7

If the probability calculated from a chi-square test is less than 0.05, what conclusion should be drawn?

Accepted Answer

The hypothesis should be rejected because the data are not consistent with it.

Question 8

Which of the following best describes the relationship between crossing over and genetic recombination?

Accepted Answer

Crossing over increases genetic recombination by exchanging segments between homologous chromosomes.

Question 9

A plant heterozygous for seed color and seed shape (YyRr) is crossed with a plant homozygous recessive for both traits (yyrr). If the genes are unlinked, what is the expected phenotypic ratio among the offspring?

Accepted Answer

1:1:1:1

Question 10

Why might the observed offspring ratios in a dihybrid testcross deviate from the expected 1:1:1:1 ratio?

Accepted Answer

The genes are linked and do not assort independently.

Question 11

Which of the following is true regarding the construction of a genetic linkage map?

Accepted Answer

The farther apart two genes are, the higher the recombination frequency.

Question 12

If two genes are so far apart on a chromosome that crossovers between them are very frequent, what will their recombination frequency approach?

Accepted Answer

$$50\%$$

Question 13

Which of the following best explains why the physical connection between genes on the same chromosome does not always result in genetic linkage?

Accepted Answer

Crossing over can separate genes that are far apart on the same chromosome.

Question 14

Which of the following is a correct interpretation of a recombination frequency of 10% between two genes?

Accepted Answer

The genes are 10 map units apart on the same chromosome.

Question 15

What is the main reason that the observed number of recombinant offspring may differ from the expected number in a genetic cross?

Accepted Answer

Random fluctuations due to chance.

Question 16

Which of the following statements about the linear order of genes on a chromosome is correct?

Accepted Answer

The linear order of genes is identical in all genetic maps, but the spacing between genes may differ.

Question 17

If a chi-square test yields a probability value greater than 0.05, what does this indicate about the hypothesis being tested?

Accepted Answer

The observed data are not statistically significant, and the hypothesis cannot be rejected.

Question 18

Which of the following best describes the effect of crossing over on the inheritance of genes located close together on the same chromosome?

Accepted Answer

Genes that are close together are less likely to be separated by crossing over.

Question 19

Which of the following is a direct result of independent assortment during meiosis?

Accepted Answer

Genes located on different chromosomes assort independently.

The Chromosomal Basis of Inheritance and Genetic Linkage

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