CLEP Biology Mendelian Inheritance Patterns 4 — Questions and Answers
Question 1: A trait appears in every generation of a pedigree and affects both males and females equally. Affected individuals always have at least one affected parent. This pattern is most consistent with:
- Autosomal dominant inheritance (Correct answer)
- Autosomal recessive inheritance
- X-linked recessive inheritance
- Mitochondrial inheritance
Correct answer: Autosomal dominant inheritance
Autosomal dominant traits appear in every generation (no skipping), affect both sexes equally, and require only one dominant allele.
Question 2: In Labrador retrievers, coat color is controlled by two genes: E (extension) and B (brown). A dog with genotype B_E_ is black, B_ee is yellow, bbE_ is chocolate, and bbee is yellow. This is an example of:
- Recessive epistasis (Correct answer)
- Codominance
- Incomplete dominance
- Sex-linked inheritance
Correct answer: Recessive epistasis
The ee genotype masks the B locus entirely, causing yellow regardless of the B allele — this is recessive epistasis.
Question 3: If the frequency of an autosomal recessive disease in a population is 1/10,000, what is the approximate carrier frequency according to the Hardy-Weinberg principle?
- 1/50 (Correct answer)
- 1/100
- 1/200
- 1/10,000
Correct answer: 1/50
q² = 1/10,000 so q = 1/100; carrier frequency = 2pq ≈ 2(1)(1/100) = 1/50.
Question 4: A cross between a black chicken (BB) and a white chicken (bb) produces all blue-grey (splash) offspring. When two splash chickens are crossed, the expected offspring ratio is:
- 1 black : 2 blue-grey : 1 white (Correct answer)
- 3 black : 1 white
- 1 black : 1 white
- All blue-grey
Correct answer: 1 black : 2 blue-grey : 1 white
Incomplete dominance: Bb (splash) × Bb gives 1 BB (black) : 2 Bb (splash) : 1 bb (white).
Question 5: Pleiotropy refers to a situation in which:
- A single gene influences multiple, seemingly unrelated phenotypic traits (Correct answer)
- Multiple genes each contribute to a single quantitative trait
- One gene masks the expression of another gene
- Two alleles are both fully expressed in heterozygotes
Correct answer: A single gene influences multiple, seemingly unrelated phenotypic traits
Pleiotropy occurs when one gene has multiple phenotypic effects, as seen with PKU affecting brain, skin, and hair pigmentation.
Question 6: Two true-breeding strains of mice are crossed: one with normal fur (AABB) and one with albino fur (aabb). F1 mice are all normal (AaBb). When F1 mice are interbred, the F2 ratio is 9 normal : 3 brown : 4 albino. The 4 albino class includes which genotypes?
- aaB_ and aabb (Correct answer)
- aaBB and aabb
- Aabb and aabb
- aaBb only
Correct answer: aaB_ and aabb
The aa genotype causes albinism regardless of the B locus, so aaB_ (3/16) and aabb (1/16) together equal 4/16 albino.
Question 7: A geneticist performs a cross and observes a 9:7 ratio in the offspring. This ratio most likely results from:
- Duplicate recessive epistasis where either locus being homozygous recessive gives the same phenotype (Correct answer)
- Simple dominant epistasis at one locus
- A standard dihybrid cross with complete dominance
- Codominance at both loci
Correct answer: Duplicate recessive epistasis where either locus being homozygous recessive gives the same phenotype
A 9:7 ratio arises when A_B_ gives one phenotype and all other genotypes (A_bb, aaB_, aabb) give the same alternative phenotype.
CLEP Biology Mendelian Inheritance Patterns 4
A trait appears in every generation of a pedigree and affects both males and females equally.
Affected individuals always have at least one affected parent.
This pattern is most consistent with: