AP Biology Genetics, Heredity, and More Practice Problems (Answer Key on the bottom)

I. Heredity & Genetics

1. Mendelian Genetics

1. A heterozygous (Aa) plant is crossed with a homozygous recessive (aa) plant.

a) What are the possible genotypes of the offspring?

b) What is the genotypic ratio?

c) What is the phenotypic ratio if A is dominant over a?

2. In peas, round seeds (R) are dominant over wrinkled seeds (r). A heterozygous plant (Rr) is crossed with a homozygous dominant (RR) plant.

a) What are the possible genotypes of the offspring?

b) What is the phenotypic ratio?

2. Non-Mendelian Genetics

3. In snapdragons, red (RR) and white (WW) flowers show incomplete dominance, producing pink (RW) flowers.

a) If two pink flowers (RW) are crossed, what is the expected genotypic ratio?

b) What is the expected phenotypic ratio?

4. Blood type is an example of codominance and multiple alleles. A man with blood type AB has a child with a woman who has blood type O.

a) What are the possible blood types of their child?

b) What is the probability of each blood type occurring?

3. Chi-Square Analysis

5. A farmer is breeding chickens and expects a 3:1 ratio of red-feathered to white-feathered chickens in the offspring. However, the actual results show 76 red and 24 white.

a) Calculate the expected values for each phenotype.

b) Use the chi-square formula to determine if the difference is statistically significant.

II. Meiosis & Genetic Variation

1. Meiosis

6. Meiosis creates genetic variation through crossing over and independent assortment.

a) Explain how crossing over contributes to genetic diversity.

b) How does independent assortment differ from crossing over in terms of genetic variation?

7. A sperm cell contains 23 chromosomes. Where do these chromosomes come from, and how does meiosis ensure genetic diversity?

2. Meiosis Errors

8. What is nondisjunction, and during which phases of meiosis can it occur?

9. If a person has an extra 21st chromosome, what disorder do they have?

10. If a female has only one X chromosome (XO), what disorder does she have?

III. Population Genetics & Evolution

1. Hardy-Weinberg Equilibrium

11. A population of 500 frogs includes 375 dark green and 125 light green frogs. Dark green (D) is dominant to light green (d).

a) What is the frequency of the recessive allele (q)?

b) What is the frequency of the dominant allele (p)?

c) What are the expected genotype frequencies (p², 2pq, q²)?

2. Genetic Drift & Natural Selection

12. Explain the difference between the bottleneck effect and the founder effect. Give an example of each.

13. Identify which type of natural selection is occurring in each scenario:

a) Birds with extremely long and short beaks survive better than birds with medium beaks.

b) In a population of rabbits, white fur is advantageous in snowy environments, so more rabbits with white fur survive and reproduce.

c) Human babies with very low or very high birth weights have lower survival rates than those of average weight.

IV. Speciation & Evolution

1. Reproductive Isolation

14. Match the following reproductive barriers with their descriptions:

• Temporal isolation

• Behavioral isolation

• Mechanical isolation

• Hybrid sterility

a) A male frog’s mating call is not recognized by females of a different frog species.

b) Two flowers live in the same area, but one blooms in the spring and the other in the fall.

c) A horse and a donkey can mate, but their offspring (a mule) cannot reproduce.

d) Two species of insects have differently shaped reproductive organs that prevent mating.

2. Rates of Evolution

15. What is the difference between gradualism and punctuated equilibrium? Provide an example of each.

Answer Key

I. Heredity & Genetics

1. Mendelian Genetics

1.

a) Possible genotypes: Aa, aa

b) Genotypic ratio: 1 Aa : 1 aa

c) Phenotypic ratio: 1 dominant : 1 recessive

2.

a) Possible genotypes: RR, Rr

b) Phenotypic ratio: 100% round seeds

2. Non-Mendelian Genetics

3. a) Genotypic ratio: 1 RR : 2 RW : 1 WW

b) Phenotypic ratio: 1 red : 2 pink : 1 white

4. a) Possible blood types: A, B

b) Probability: 50% Type A, 50% Type B

3. Chi-Square Analysis

5. a) Expected values: (75 red, 25 white) based on a 3:1 ratio

b) Chi-square formula:

X² = ((76-75)² / 75) + ((24-25)² / 25) = 0.053

Since X² < 3.841 (cutoff for p = 0.05), we fail to reject the null hypothesis—deviation is likely due to chance.

II. Meiosis & Genetic Variation

1. Meiosis

6. a) Crossing overallows homologous chromosomes to exchange genetic material, creating unique combinations.

b) Independent assortmentrandomly distributes chromosomes into gametes, increasing genetic diversity.

7. The 23 chromosomes in a sperm cell come from both maternal and paternal homologous chromosomes, randomly sorted due to independent assortment and crossing over.

2. Meiosis Errors

8. Nondisjunctionoccurs when chromosomes fail to separate properly during Anaphase I or IIof meiosis.

9. Trisomy 21 (Down Syndrome)

10. Turner Syndrome (XO)

III. Population Genetics & Evolution

1. Hardy-Weinberg Equilibrium

11.

a) q = 0.5

b) p = 0.5

c) Genotypic frequencies: p² = 0.25, 2pq = 0.50, q² = 0.25

2. Genetic Drift & Natural Selection

12.

• Bottleneck effect: Drastic reduction in population size (e.g., natural disaster).

• Founder effect: Small group colonizes new area (e.g., island settlers).

13.

a) Disruptive selection

b) Directional selection

c) Stabilizing selection

IV. Speciation & Evolution

1. Reproductive Isolation

14.

a) Behavioral isolation

b) Temporal isolation

c) Hybrid sterility

d) Mechanical isolation

2. Rates of Evolution

15.

• Gradualism: Slow, continuous change (e.g., horse evolution).

• Punctuated Equilibrium: Rapid changes between long periods of stability (e.g., Cambrian explosion).