Question

Carry out a tri-hybrid cross between XX(tall) YY(fat) ZZ(fair) and xx(short) yy(slim) zz(black). Find their genotypic and phenotypic ratios.

Answer 1

Answer:

Genotypic ratio = 100% XxYyZz

Phenotypic ratio = 100% tall, fat, fair.

Explanation:

For a trihybrid cross involving the genes XX which codes for tallness, YY which codes for fatness, and ZZ which codes for fairness with their alternate forms being xx, yy, and zz respectively; each gene will segregate into their respective alleles and combine to form gametes during meiosis, such that:

XXYYZZ ----> XYZ, XYZ, XYZ, XYZ, XYZ, XYZ, XYZ, XYZ

xxyyzz -----> xyz, xyz, xyz, xyz, xyz, xyz, xyz, xyz

These gametes then combine randomly during fertilization to give all XxYyZz offspring.

                XYZ    x    xyz

                       XxYyZz

Since X is dominant over x, Y is dominant over y, and Z is dominant over z, then XxYyZz individuals that are produced from the cross would be tall, fat, and fair. Hence

Genotypic ratio = 100% XxYyZz

Phenotypic ratio = 100% tall, fat, fair.

See the attached image from the Punnet's square analysis.