AP Biology Practice Questions- . Linkage & Beyond (Answer Key at the End)

Section 1: Linkage & Recombination

1. Multiple Choice

Thomas Hunt Morgan discovered that genes located on the same chromosome tend to be inherited together. Which of the following best explains why some linked genes are sometimes separated?

A) Independent assortment

B) Nondisjunction during meiosis

C) Crossing over during prophase I

D) DNA replication errors

2. Free Response

Morgan’s data for linked genes in fruit flies showed 965 parental-type offspring and 206 recombinant offspring.

a) Calculate the recombination frequency.

b) Explain what this frequency tells us about the distance between these genes.

Section 2: Gene Mapping

3. Matching

Match the scientist to their contribution:

1. Thomas Hunt Morgan

2. Alfred Sturtevant

3. Hermann Muller

4. Theodosius Dobzhansky

5. Ernst Mayr

A) Developed the Biological Species Concept

B) Studied the effects of radiation on mutations

C) Used recombination frequencies to create the first gene maps

D) Conducted fruit fly experiments showing genes are on chromosomes

E) Connected genetics with evolution, studied Drosophila populations

Section 3: Evolution & Speciation

4. True or False

• A species is defined only by physical characteristics.

• Allopatric speciation occurs due to geographic isolation.

• Genetic drift has no effect on small populations.

• The closer genes are on a chromosome, the higher the chance of recombination.

5. Free Response

Ernst Mayr proposed the Biological Species Concept (BSC).

a) Define the Biological Species Concept.

b) Provide one limitation of this definition.

Section 4: Experimental Scenarios

6. Experimental Design

Alfred Sturtevant used recombination frequencies to create gene maps. Suppose you are studying three genes: X, Y, and Z. You obtain the following recombination frequencies:

• X-Y = 12%

• Y-Z = 8%

• X-Z = 20%

a) Draw a simple linkage map showing the order of these genes.

b) If a fourth gene, W, is found to have a recombination frequency of 25% with gene X, where is W likely located?

Answer Key

1. Multiple Choice Answer:

C) Crossing over during prophase I

2. Free Response Answer:

a) Recombination frequency = (Recombinants / Total Offspring) × 100

• (206 + 185) / (965 + 944 + 206 + 185) × 100 = 17%

b) A recombination frequency of 17% means these genes are 17 map units (centimorgans) apart on the chromosome. The closer genes are, the less likely they will be separated by crossing over.

3. Matching Answer:

1 - D) Morgan → Genes are on chromosomes

2 - C) Sturtevant → Gene mapping using recombination frequency

3 - B) Muller → Radiation and mutations

4 - E) Dobzhansky → Connected genetics and evolution

5 - A) Mayr → Biological Species Concept

4. True or False Answers:

• False – A species is NOT defined only by physical characteristics (reproductive isolation matters).

• True – Allopatric speciation occurs due to geographic isolation.

• False – Genetic drift strongly affects small populations.

• False – The closer genes are, the lower the chance of recombination.

5. Free Response Answer:

a) The Biological Species Concept defines a species as a group of populations that can interbreed and produce viable, fertile offspring but are reproductively isolated from other groups.

b) A limitation is that BSC does not apply to asexual organisms (e.g., bacteria) or fossil species where reproductive isolation cannot be tested.

6. Experimental Design Answer:

a) The gene order is:

X—Y—Z (because X-Y is 12%, Y-Z is 8%, and X-Z is 20%).

b) If W has a recombination frequency of 25% with X, it is likely farther away than Z or on a different chromosome if the recombination frequency is too high.