Test crosses are performed to determine the genotype of an organism. A farmer buys a goat whose owner claims has sired fainting goats, though Gary has never actually fainted himself. What type of goat (genotype/phenotype) should the farmer mate with Gary to determine if Gary really is a carrier. Explain your reasoning showing the cross.

A goat that faints with a genotype (gg)

Explanation:

Ideally, test crosses are used in genetics to determine the genotype of an unknown organism (usually a dominant phenotype). In a case of goats with a fainting gene (G), the dominant allele is G while the recessive allele is g. G codes for no fainting while g codes for fainting in goats.

The farmer wants to ascertain whether Gary, a goat he bought, is indeed a carrier of the fainting trait or simply a heterozygous (Gg). He performs a test cross by crossing Gary (Gg) with a goat that is homozygous (gg) for the recessive phenotype (fainting). In this cross, if Gary were truly a carrier/heterozygous, half (1/2) of the offsprings produced will be phenotypically fainting goats with genotype (gg). If not, all offsprings will not express the fainting trait.

g g

G. Gg. Gg

g. gg. gg