CLEP Biology Mendelian Inheritance Patterns 2 — Questions and Answers
Question 1: In a dihybrid cross between two heterozygous parents (AaBb × AaBb), what fraction of offspring are expected to be homozygous recessive for both traits (aabb)?
- 1/16 (Correct answer)
- 3/16
- 9/16
- 1/4
Correct answer: 1/16
Each trait independently produces 1/4 homozygous recessive offspring, so (1/4)(1/4) = 1/16 for both.
Question 2: A man with blood type A (genotype I^A i) and a woman with blood type B (genotype I^B i) have children. What is the probability that a child will have blood type O?
- 1/4 (Correct answer)
- 1/2
- 3/4
- 0
Correct answer: 1/4
The cross I^A i × I^B i produces I^A I^B, I^A i, I^B i, and ii in equal 1/4 proportions, so 1/4 will be type O.
Question 3: Which of the following best describes the concept of 'gene interaction' in the context of epistasis?
- One gene masks or modifies the expression of another gene (Correct answer)
- Two genes on the same chromosome assort together
- A single gene controls multiple phenotypic traits
- Alleles at one locus blend to produce an intermediate phenotype
Correct answer: One gene masks or modifies the expression of another gene
Epistasis occurs when one gene's alleles suppress or alter the phenotypic expression of a different gene.
Question 4: A plant with red flowers (RR) is crossed with a white-flowered plant (rr), producing all pink offspring (Rr). This pattern of inheritance is an example of:
- Incomplete dominance (Correct answer)
- Codominance
- Complete dominance
- Epistasis
Correct answer: Incomplete dominance
Incomplete dominance produces an intermediate phenotype (pink) because neither allele is fully dominant over the other.
Question 5: In humans, the allele for attached earlobes (a) is recessive to free earlobes (A). Two parents with free earlobes have a child with attached earlobes. What are the genotypes of the parents?
- Aa × Aa (Correct answer)
- AA × Aa
- AA × AA
- Aa × aa
Correct answer: Aa × Aa
Both parents must be Aa (carriers) to produce an aa child while themselves expressing the dominant phenotype.
Question 6: The law of segregation states that:
- Allele pairs separate during gamete formation so each gamete carries only one allele per gene (Correct answer)
- Genes on different chromosomes assort independently during meiosis
- The dominant allele always masks the recessive allele in heterozygotes
- Traits blend together in offspring of two different parents
Correct answer: Allele pairs separate during gamete formation so each gamete carries only one allele per gene
Mendel's law of segregation holds that the two alleles of a gene separate during meiosis, with each gamete receiving one allele.
Question 7: If a trait is autosomal recessive, which of the following pedigree observations would be INCONSISTENT with that inheritance pattern?
- An affected child with two unaffected parents who are carriers
- Skipping of generations (trait appears in grandchild but not parent)
- An affected father passing the trait directly to all sons (Correct answer)
- Equal frequency of the trait in males and females
Correct answer: An affected father passing the trait directly to all sons
An autosomal recessive trait is not sex-linked, so an affected father does NOT pass it to all sons — sons must also inherit a recessive allele from the mother.
CLEP Biology Mendelian Inheritance Patterns 2
In a dihybrid cross between two heterozygous parents (AaBb × AaBb), what fraction of offspring are expected to be homozygous recessive for both traits (aabb)?