Question

On performing a test cross, 1:1 phenotypic ratio is obtained in the offspring; this indicates

• A. Alleles are codominant
• B. Heterozygous condition of the dominant parent
• C. Homozygous condition of dominant parent
• D. Alleles are dominant

Answer 1

The correct option is B Heterozygous condition of the dominant parent

In a test cross, an individual with dominant phenotype but unknown genotype is crossed with a homozygous recessive phenotype individual.

If the testing individual is heterozygous dominant then;

50% of offspring are dominant and the other 50% are recessive, i.e. 1:1 phenotypic ratio.

If the testing individual is homozygous dominant then;


All the offspring will be of dominant phenotype.