Question

A sugarcane plant with yellow pollen and wavy leaves is crossed with a plant with yellow pollen and smooth leaves. Seed are collected and germinated. The following results are obtained in the progeny:
153 yellow pollen, wavy leaves
145 yellow pollen, smooth leaves
48 white pollen, wavy leaves
51 white pollen, smooth leaves

a. For each locus (trait): Assign appropriate symbols for the alleles of the genes, indicate the dominance interaction between the two alleles, and give all possible genotypes and their associated phenotypes
b. Give the genotypes of the parents of this cross.
c. Give the expected genotypic and phenotypic ratios of the progeny of this cross.

Answer 1

Answer:

a.

i) Y and y represent Yellow and white alleles for the pollen color gene; where Y (yellow) is dominant over y (white).

ii) W and w represent wavy and smooth alleles respectively for the leaf texture gene. W (wavy) is dominant over w (smooth).

YYWW, YyWW, YyWw, YYWw- yellow, wavy phenotype

YYww, Yyww- yellow, smooth phenotype

yyWW, yyWw- white, wavy phenotype

yyww- white, smooth phenotype

b) yellow pollen and wavy leaves (YyWw) × yellow pollen and smooth leaves (Yyww)

c) Expected genotypic and phenotypic ratio of progeny: 3:3:1:1

Explanation:

This question involves two distinct genes; one coding for pollen color and the other for leaf texture. Let Y and y represent Yellow and white alleles respectively for the pollen color gene; where Y (yellow) is dominant over y (white) while W and w represent wavy and smooth alleles respectively for the leaf texture gene; W allele (wavy) is dominant over w allele (smooth).

Next, we convert the progeny number to phenotypic ratio by dividing each number by the smallest number (48)

yellow pollen, wavy leaves= 153/48 =3.18

yellow pollen, smooth leaves= 145/48= 3.02

white pollen, wavy leaves= 48/48= 1

white pollen, smooth leaves= 51/48= 1.06

Approximately, the phenotypic ratio of the progeny is 3:3:1:1

According to the question, a parent with with yellow pollen and wavy leaves will have genotype YyWw because white pollen (w) and smooth leaf (s) was produced in the progeny. Also, the other parent with yellow pollen and smooth leaves will have genotype: Yyww. In a cross between these two parents i.e. YyWw × Yyww, the following gametes will be produced:

YyWw- YW, Yw, yW, yw

Yyww- Yw, Yw, yw, yw

Using these gametes in a punnet square (see attachment), the following 16 offsprings will be produced in a ratio 3:3:1:1

yellow pollen, wavy leaves (Y_W_) 6

yellow pollen, smooth leaves (Y_ww) 6

white pollen, wavy leaves (yyW_) 2

white pollen, smooth leaves (yyww) 2