Question

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.

Answer 1

Answer:

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

Answer 2

Answer:

a goat with  homozygote recessive allele for the sired fainting. assuming ff  is used.This is the best way to know if the sired fainting goat is homozygote dominant or heterozygote dominat (carrier) for the gene.,

Explanation:

This is because test crossing is usually used to determine an unknown  genotype of a particular allele, because phenotype of an organism may not reflect the true  nature of the allele present,Therefore a known  homozygote recessive allele is crossed with the unknown genotype. The phenotype of the offspring can be used to determine  if the goat is a carrier or not.

Assuming FF represented the sired fainted dominant allele, and Ft represent the heterozygote dominant(carrier) .These  symbols were chosen because Gary  has not been fainted.We are not sure of its genotype yet.

Test Crossing.

To determine if the goat was a carrier; half of the offspring should carry  homozygote recessive allele(ff)fainted and half should  be hetrozygote dominant(Ft) for the gene in 50-50 %.

             →    Ft        X       ff.

             →     Ff Ff, ff, ff,

This shows that the goat was a carrier. However if  after the crossing, the offspring were all  heterozygote dominant for the allele;Then the goat can not be carrier for the gene.

Then;

                      FF           X    ff

                     Ft, Ft, Ft, Ft.

None will be sired fainted