Test Cross

What is Test Cross?

A cross between an individual showing a dominant phenotype, whose genotype is unknown, and an individual that is homozygous recessive for the same gene. Because the homozygous recessive parent can only produce gametes carrying the recessive allele, every offspring's phenotype is decided by the allele it receives from the unknown parent. If any offspring shows the recessive phenotype, the unknown parent must be heterozygous; if a large number of offspring all show the dominant phenotype, the unknown parent is probably homozygous dominant, although no finite number of offspring proves this with certainty.

This definition is part of the Inheritance chapter in Cambridge O Level Biology.

Concepts related to Test Cross

• homozygous recessive
• heterozygous
• 1:1 ratio
• evidence