Keystone Test Biology: Genetics and Evolution 2 — Questions and Answers
Question 1: A plant with genotype AaBb is self-fertilized. What fraction of offspring will be aabb?
- 1/16 (Correct answer)
- 1/8
- 1/4
- 3/16
Correct answer: 1/16
Each heterozygous gene pair produces 1/4 homozygous recessive offspring, so 1/4 × 1/4 = 1/16.
Question 2: Which type of mutation involves the insertion of a nucleotide into a DNA sequence?
- Substitution
- Deletion
- Frameshift (Correct answer)
- Silent
Correct answer: Frameshift
Inserting a nucleotide shifts the reading frame of all downstream codons, making it a frameshift mutation.
Question 3: During which phase of meiosis do homologous chromosomes separate?
- Meiosis I anaphase (Correct answer)
- Meiosis II anaphase
- Metaphase I
- Telophase II
Correct answer: Meiosis I anaphase
Homologous chromosomes are pulled to opposite poles during anaphase I, reducing chromosome number by half.
Question 4: A white-eyed female Drosophila (X^w X^w) is crossed with a red-eyed male (X^+ Y). What proportion of female offspring will have white eyes?
- 0% (Correct answer)
- 50%
- 100%
- 25%
Correct answer: 0%
All daughters receive X^+ from their father, making them X^+ X^w carriers with red eyes.
Question 5: What does a phylogenetic tree's branch length typically represent?
- Number of species in a clade
- Amount of evolutionary change (Correct answer)
- Geographic distance between species
- Time since speciation only
Correct answer: Amount of evolutionary change
Branch lengths on most phylogenetic trees represent the amount of evolutionary change (mutations) along that lineage.
Question 6: Which evolutionary mechanism causes random changes in allele frequency in small populations?
- Natural selection
- Gene flow
- Genetic drift (Correct answer)
- Mutation pressure
Correct answer: Genetic drift
Genetic drift is random fluctuation in allele frequencies that has the greatest effect in small populations.
Question 7: If a trait shows incomplete dominance, what will the F1 phenotype of a cross between two homozygous parents look like?
- Identical to one parent
- Identical to both parents
- Intermediate between both parents (Correct answer)
- Absent in F1
Correct answer: Intermediate between both parents
In incomplete dominance, heterozygotes display a phenotype intermediate between the two homozygous parental phenotypes.
Keystone Test Biology: Genetics and Evolution 2
A plant with genotype AaBb is self-fertilized.
What fraction of offspring will be aabb?