Chapter 12, Problem 1TYK

The dominant C allele of a gene that controls color in corn produces kernels with color; plants homozygous for a recessive c allele of this gene have colorless or white kernels. What kinds of gametes, and in what proportions, would be produced by the plants in the following crosses? What seed color, and in what proportions, would be expected in the offspring of the crosses?

a. $CC\times Cc$

b. $Cc\times cc$

c. $Cc\times Cc$

Summary Introduction

To review:

On the basis of the data for dominant and recessive traits, the types of gametes formed, the color of the seed and its proportion, for the following crosses:

a. CC x Cc

b. Cc x cc

c. Cc x Cc

Introduction:

According to the law of dominance, the dominant trait is shown in homozygous as well as heterozygous form but the recessive trait is shown only when the homozygous allelic pair is present. The color of the kernels in corn is controlled by gene ‘C’, which is dominant in producing different colors, and gene $\text{'}c\text{'}$, which is recessive and produces no color, that is, white.

Explanation of Solution

a. The cross for CC × Cc can be made as follows:

The parents have the genotype CC (colored) × Cc (colored)

The cross can be made as:

All the progenies will have colored kernels.

The CC plant produces all C gametes. Cc produces 50% of C and 50% of c gametes. Looking at the offspring produced, 50% (1/2) of homozygous (CC) colored and 50% (1/2) of heterozygous (Cc) colored plants are produced.

b. The cross for Cc × cc can be made as follows:

The parents have the genotype $Cc\left(\text{colored}\right)$ and $cc\left(\text{white}\right)$.

The cross can be made as:

The progenies have the ratio of colored kernels to white kernels as $2:2\text{}\text{ or }1:1$.

The Cc plant produces 50% of C and 50% of c gametes and the cc parent produces all c gametes. Looking at the offspring produced, 50% (1/2) of heterozygous (Cc) colored plants and 50% (1/2) of homozygous recessive plants are produced.

c. The cross for Cc × Cc can be made as follows:

The parents have the genotype Cc (colored) and Cc (colored).

The cross can be made as:

The progenies have the ratio of colored kernels to white kernels as $3:1$.

Both the Cc plants produce 50% of C and 50% of c gametes. Looking at the offspring produced, 50% (1/2) of heterozygous (Cc) colored plants, 25% (1/4) of homozygous recessive plants, and 25% (1/4) of homozygous colored plants are produced.

Conclusion

Therefore, it can be concluded that:

a. Cc produces 50% of C and 50% of c gametes. Half of homozygous (CC) colored and halh of heterozygous (Cc) colored plants are produced.

b. Cc produces 50% of C and 50% of c gametes and cc produces all c gametes. Half of heterozygous (Cc) colored plants and half of homozygous recessive plants are produced.

c. Both the Cc plants produce 50% of C and 50% of c gametes. Half of heterozygous (Cc) colored plants, 1/4 of homozygous recessive plants, and 1/4 of homozygous colored plants are produced.