|
An individual who expresses the dominant phenotype for a given gene can be either
homozygous (AA) or heterozygous (Aa). A testcross is performed to
determine the genotype of
the dominant phenotype individual. The
individual in question is crossed to a tester
(homozygous for the
recessive allele - genotypically aa).
Possibility 1: individual is AA
A cross of AA X aa would produce progeny that are all
Aa genotypically and all progeny would express the dominant phenotype.
Possibility 2: individual is Aa A cross of Aa X aa would produce progeny such that 1/2
would be of Aa genotype (dominant phenotype) and 1/2 would be of aa genotype (recessive
phenotype).
Composition of progeny phenotype allows you to determine if the individual with the dominant
phenotype is AA or Aa.
|