Answer and Explanation:
<em><u>Available data</u></em>:
- Comb shape is determined by genes at two loci (R, r and P, p).
- The walnut comb genotype is R_P_.
- The rose comb genotype is R_pp.
- The pea comb genotype is rrP_.
- The single genotype is rrpp.
a. <em>Walnut crossed with single produces 1 walnut, 1 rose, 1 pea, and 1 single offspring: </em>
Parental) RrPp x rrpp
Gametes) RP Rp rP rp rp rp rp rp
Punnet Square) RP Rp rP rp
rp <em>RrPp Rrpp rrPp rrpp</em>
rp RrPp Rrpp rrPp rrpp
rp RrPp Rrpp rrPp rrpp
rp RrPp Rrpp rrPp rrpp
F1 phenotype: 25% walnut, 25% rose, 25% pea, and 25% single.
F1 genotype: 4/16 RrPp, 1/16 Rrpp, 4/16 rrPp, 4/16 rrpp.
b. <em>Rose crossed with pea produces 20 walnut offspring</em>.
Parental) RRpp x rrPP
Gametes) Rp Rp Rp Rp rP rP rP rP
Punnet Square) Rp Rp Rp Rp
rP RrPp RrPp RrPp RrPp
rP RrPp RrPp RrPp RrPp
rP RrPp RrPp RrPp RrPp
rP RrPp RrPp RrPp RrPp
F1 phenotype: 100% walnut.
F1 genotype: 16/16 RrPp.
c. <em>Pea crossed with single produces 1 single offspring</em>.
This is not possible, because the pea genotype involves <u>at least</u> one dominant allele P. There are two possible crosses: <em>rrPp x rrpp</em>, which must produce half of the progeny pea and the other half single, or <em>rrPP x rrpp</em> which produce a whole pea progeny with no single offspring.
Parental) rrPp x rrpp
Gametes) rP rp rP rp rp rp rp rp
Punnet Square) rP rp rP rp
rp <em>rrPp rrpp rrPp rrpp</em>
rp rrPp rrpp rrPp rrpp
rp rrPp rrpp rrPp rrpp
rp rrPp rrpp rrPp rrpp
F1 phenotype: 50% pea, and 50% single.
F1 genotype: 8/16 rrPp, 8/16 rrpp.
d. <em>Rose crossed with pea produces 2 walnut, 1 single, and 1 pea offspring</em>.
This is not possible, because having one of the parents with a rose phenotype involves <u>at least one R allele</u>, which means that <u>there must be rose phenotype</u> in the progeny.
Parental) Rrpp x rrPp
Gametes) Rp Rp rp rp rP rP rp rp
Punnet Square) Rp Rp rp rp
rP <em> RrPp </em> RrPp <em> rrPp</em> rrPp
rP RrPp RrPp rrPp rrPp
rp <em>Rrpp</em> Rrpp <em>rrpp </em> rrpp
rp Rrpp Rrpp rrpp rrpp
F1 phenotype: 25% walnut, 25% rose, 25% pea, and 25% single.
F1 genotype: 4/16 RrPp, 1/16 Rrpp, 4/16 rrPp, 4/16 rrpp.
e. <em>Rose crossed with single produces 31 rose offspring</em>.
Parental) RRpp x rrpp
Gametes) Rp Rp Rp Rp rp rp rp rp
Punnet Square) Rp Rp Rp Rp
rp Rrpp Rrpp Rrpp Rrpp
rp Rrpp Rrpp Rrpp Rrpp
rp Rrpp Rrpp Rrpp Rrpp
rp Rrpp Rrpp Rrpp Rrpp
F1 phenotype: 100% rose (31 individuals equal 100% of the progeny).
F1 genotype: 16/16 Rrpp.
f. <em>Rose crossed with single produces 10 rose and 11 single offspring.</em>
Parental) Rrpp x rrpp
Gametes) Rp Rp rp rp rP rP rp rp
Punnet Square) Rp Rp rp rp
rp Rrpp Rrpp rrpp rrpp
rp Rrpp Rrpp rrpp rrpp
rp Rrpp Rrpp rrpp rrpp
rp Rrpp Rrpp rrpp rrpp
F1 phenotype: 50% rose, 50% single.
F1 genotype: 8/16 Rrpp, 8/16 rrpp.