Consider 3 gene loci in the pea plant. Locus 1 affects seed color; allele G for

Question

Consider 3 gene loci in the pea plant. Locus 1 affects seed color; allele G for green, g for yellow. Locus 2 affects seed shape; allele R for round, r for wrinkled. Locus 3 affects flower color; allele B for red, b for white. Each upper case allele is completely dominant to their corresponding lower case, recessive allele. Each locus is on a different non-homologous chromosome; so, the loci segregate or sort independently from each other during meiosis. Two parent pea plants, each of genotype GgRrBb, are mated with each other. That mating produced 1000 progeny. a. What fraction of the gametes of the parents are expected to contain only recessive alleles? b. How many phenotypic classes are expected among the progeny? c. What fraction of the progeny are expected to have the combination green seed, round seed, and red flowers? d. How many progeny are expected to have the combination yellow seed, wrinkled seed, and white flowers? e. How many genotypic classes are expected among the progeny? SHOW ALL YOUR CALCULATIONS.

Explanation / Answer

Parent 1 Genotype = GgRrBb
Parent 1 Gametes = (G/g)(R/r)(B/b)
Parent 2 Genotype = GgRrBb
Parent 2 Gametes = (G/g)(R/r)(B/b)

Answer a.
For each parent we have two choices per allele, so for 3 alleles we end up with 2*2*2=8 choices
Out of this only 1 choice which is (G/g)(R/r)(B/b) = grb is the alll recessive one.
Hence fraction = 1/8

Answer b.
For each trait we have two possible phenotypes, so for 3 traits we end up with 2*2*2=8 phenotypic classes

Answer c.
Green Seed + Round Seed + Red Flowers = (GG, Gg, gG)(RR, Rr, rR)(BB, Bb, bB)
For any allele there are 4 possible choices = DominantDominant, DominantRecessive, RecessiveDominant, RecessiveRecessive.
Hence we end up with a chance of (3/4) * (3/4) * (3/4) = 27/64

Answer d.
Yellow Seed + Wrinkled Seed + White Flowers = (gg)(rr)(bb)
For any allele there are 4 possible choices = DominantDominant, DominantRecessive, RecessiveDominant, RecessiveRecessive.
Hence we end up with a chance of (1/4) * (1/4) * (1/4) = 1/64

Answer e.
For any allele there are 3 possible genotypes = Homozygous Dominant, Heterozygous, Homozygous Recessive
Hence, for 3 alleles, we have 3*3*3 = 27 genotypic classes

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