Question

What is test-cross? Show diagrammatic representation of it.

Hint:

Test-crosses help determine the genotype of an individual with a dominant phenotype by crossing it with a homozygous recessive individual.

Answer 1

Step 1: Understanding Test-cross.
A test-cross is a genetic cross between an individual with an unknown genotype (usually heterozygous) and an individual with a known homozygous recessive genotype. This is used to determine whether the unknown individual is homozygous or heterozygous for a particular trait.

Step 2: Diagrammatic representation.
Consider a parent with the genotype \( A_1A_2 \) (unknown genotype) and a homozygous recessive individual \( a_1a_1 \). The test-cross will result in offspring that show a 1:1 ratio of dominant to recessive phenotypes if the unknown parent is heterozygous, or all offspring will show the dominant phenotype if the unknown parent is homozygous dominant.

Step 3: Conclusion.
A test-cross is an important tool for determining the genotype of an individual based on its offspring's phenotype.