Test Cross

In genetics, a test cross, first introduced by Gregor Mendel, is used to determine if a group exhibiting a dominant trait is homozygous or heterozygous for that trait. More simply put, test crosses determine the genotype of an individual with a dominant phenotype.

Test crosses involve breeding the individual in question with another individual that expresses a recessive version of the same trait. If all offspring display the dominant phenotype, the individual in question is homozygous dominant; if the offspring display both dominant and recessive phenotypes, then the individual is heterozygous.

In some sources, the "test cross" is defined as being a type of backcross between the recessive homozygote and F1 generation or F2 generation crossed with recessive parent is said to be a test cross.The ratios in test cross are always equal e.g; if a heterozygous white(Yy)is crossed with homozygous yellow,then 2 gametes formed will be Yy and yy. It means 50% plants will be of white color and 50% plants will be of yellow color.

If the individual being tested produces any recessive offspring (except in cases of incomplete penetrance) its genotype is heterozygous. If all the offspring are phenotypically dominant, its genotype is homozygous.

For other crosses look for Di-hybrid and mono-hybrid crosses, these can provide more accurate and more detailed information on genotypes behind phenotypes in organisms.

Definition: Mendel devised a cross which is used to test the genotype of an individual showing a dominant phenotype. It is a mating in which an individual showing an dominant phenotype is cross with an individual showing its recessive phenotype.