Multiple Choice
Which of the following best describes a dihybrid cross in genetics?
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2. Mendel's Laws of Inheritance
Dihybrid Cross
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A 1:1:1:1 ratio of offspring from a dihybrid testcross indicates that ___________.
A
the two genes are completely linked
B
there is incomplete dominance at both loci
C
epistasis is occurring between the two genes
D
the two genes assort independently
Verified step by step guidance1
Understand that a dihybrid testcross involves crossing an individual heterozygous for two genes (genotype AaBb) with an individual homozygous recessive for both genes (genotype aabb).
Recall that if the two genes assort independently (i.e., are on different chromosomes or far apart on the same chromosome), the expected phenotypic ratio of offspring from this testcross is 1:1:1:1.
Recognize that a 1:1:1:1 ratio means each of the four possible phenotypes (AB, Ab, aB, ab) appears with equal frequency, indicating independent assortment without linkage or interaction.
Contrast this with other scenarios: complete linkage would produce mostly parental types, incomplete dominance would alter phenotypic ratios differently, and epistasis would modify expected ratios away from 1:1:1:1.
Conclude that observing a 1:1:1:1 ratio in a dihybrid testcross is evidence that the two genes assort independently according to Mendel's second law.
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