What is the primary genetic difference between a test cross and a back cross?

Answer and explanation

Correct answer: D. A test cross is always made between an individual of unknown genotype and the homozygous recessive parent

Answer: A test cross is always made between an individual of unknown genotype and the homozygous recessive parent.\nWhy not the others: Crossing with homozygous dominant is a dominant backcross that masks recessive alleles; Heterozygous siblings is an intercross; Different species cross is an interspecific hybridization.
  1. Step 1: A back cross refers to crossing an hybrid with either of its two parental genotypes (dominant or recessive).
  2. Step 2: A test cross is a specific type of back cross where an individual displaying the dominant phenotype (which could be or ) is crossed exclusively with the homozygous recessive parent ().
  3. Step 3: Because the recessive parent contributes only recessive alleles, the phenotypic ratio of the offspring directly reveals the unknown genotype (1:0 if homozygous dominant, 1:1 if heterozygous).

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