Question 1

Which of the following best explains why Mendel observed a 9:3:3:1 ratio in the F2 generation of his dihybrid crosses?

Accepted Answer

Because the two genes were located on different chromosomes and assorted independently during meiosis.

Question 2

In a dihybrid cross between true-breeding smooth yellow (SS YY) and wrinkled green (ss yy) pea plants, what is the expected phenotypic ratio in the F2 generation if the genes assort independently?

Accepted Answer

$$9:3:3:1$$

Question 3

Which stage of meiosis is primarily responsible for the law of independent assortment as illustrated in the provided images?

Accepted Answer

Metaphase I

Question 4

If two genes are completely linked (no crossing over occurs), what proportion of the gametes will be recombinant?

Accepted Answer

$$0\%$$

Question 5

A testcross between a dihybrid individual (AaBb) and a double recessive (aabb) produces the following offspring: 40% AB, 40% ab, 10% Ab, 10% aB. What is the recombination frequency between the two genes?

Accepted Answer

$$20\%$$

Question 6

During which substage of prophase I does crossing over (recombination) occur?

Accepted Answer

Pachytene

Question 7

If the recombination frequency between two genes is $$1.4\%$$, what is their distance apart on a genetic map?

Accepted Answer

$$1.4$$ centiMorgans (cM)

Question 8

Why do genetic maps based on recombination frequencies sometimes underestimate the true physical distance between two genes?

Accepted Answer

Because double crossovers can occur, which restore the parental combination and are not detected as recombinants.

Question 9

In the context of genetic linkage, what does a recombination frequency of $$50\%$$ indicate about the relationship between two genes?

Accepted Answer

The genes are either on different chromosomes or far apart on the same chromosome and assort independently.

Question 10

A geneticist observes that two genes in Drosophila have a recombination frequency of $$37.5\% in a $$single experiment, but a genetic map predicts they are $$57.6$$ map units apart. What is the most likely explanation for this discrepancy?

Accepted Answer

Double crossovers between the genes are not detected, leading to an underestimate of the true distance in the experiment.

Question 11

Which of the following statements about crossing over is TRUE?

Accepted Answer

Crossing over occurs between homologous chromosomes during meiosis I and increases genetic diversity.

Question 12

If two genes are 36.9 map units apart on the X chromosome, what percentage of gametes are expected to be recombinant for these genes?

Accepted Answer

$$36.9\%$$

Question 13

Which of the following best describes a chiasma?

Accepted Answer

A physical site where homologous chromosomes exchange genetic material during meiosis.

Question 14

In a cross where two genes are incompletely linked and crossover occurs in $$20\% of $$meioses, what proportion of the gametes will be recombinant?

Accepted Answer

$$20\%$$

Question 15

Which of the following is a direct consequence of the linear arrangement of genes on a chromosome?

Accepted Answer

The frequency of recombination between two genes is proportional to their physical distance apart.

Question 16

A geneticist is mapping three genes (A, B, and C) on a chromosome. The recombination frequency between A and B is $$10\%$$, between B and C is $$15\%$$, and between A and C is $$25\%. $$What is the most likely order of the genes?

Accepted Answer

A - B - C

Question 17

Which of the following would be the best experimental approach to minimize the underestimation of genetic distances due to double crossovers?

Accepted Answer

Use multiple small intervals between genes to construct the genetic map.

Question 18

Which of the following is NOT a modification to simple Mendelian inheritance?

Accepted Answer

Complete dominance with 100% penetrance

Question 19

In a testcross, if the observed number of parental phenotypes is significantly higher than expected under independent assortment, what is the most likely explanation?

Accepted Answer

The genes are linked and located close together on the same chromosome.

Question 20

Which of the following equations correctly calculates the recombination frequency between two genes?

Accepted Answer

$$	ext{Recombination\ frequency} = \frac{	ext{Number\ of\ recombinant\ offspring}}{	ext{Total\ number\ of\ offspring}} 	imes 100\%$$

Lecture 6

Study Guide - Practice Questions

Study Guide - Flashcards