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Biology Mendelian Inheritance Patterns Flashcards

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  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:

    Answer: Autosomal dominant inheritance

    Autosomal dominant traits appear in every generation (no skipping), affect both sexes equally, and require only one dominant allele.

  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:

    Answer: Recessive epistasis

    The ee genotype masks the B locus entirely, causing yellow regardless of the B allele — this is recessive epistasis.

  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?

    Answer: 1/50

    q² = 1/10,000 so q = 1/100; carrier frequency = 2pq ≈ 2(1)(1/100) = 1/50.

  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:

    Answer: 1 black : 2 blue-grey : 1 white

    Incomplete dominance: Bb (splash) × Bb gives 1 BB (black) : 2 Bb (splash) : 1 bb (white).

  5. Pleiotropy refers to a situation in which:

    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.

  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?

    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.

  7. A geneticist performs a cross and observes a 9:7 ratio in the offspring. This ratio most likely results from:

    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.