Question

List all gametes that could be made by a pea plant heterozygous for seed color, seed shape, and pod shape (YyRrIi; see Table 14.1). How large a Punnett square would you need to draw to predict the offspring of a self-pollination of this “trihybrid”?

Short answer

A pea plant that is heterozygous for seed color, seed shape, and pod shape will be called trihybrid that will produce eight different types of gametes. The gametes produced from heterozygous trihybrid (YyRrIi)will be: YRI, YRi, YrI, Yri, yRI, yRi, yrI, and yri.

The Punnett square will contain 64 types of offspring that will occupy 8 rows and 8 columns.

Step-by-step solution

Self-Pollination

Self-pollination is one form of pollination when gametophytes (pollen and ovary) of the same flower or different flowers from the same plant fuse. To check the dominant and recessive traits, Mendel used this mechanism. He self-fertilized the hybrid plants that he obtained after cross-fertilization of two pure plants.

Gametes

Gamete formation is the main step in sexual reproduction that involves the fusion of the gametes produced by two different sex cells. These gametes are produced during reproduction and develop into complete offspring containing a unique combination of alleles from gametes.

Gametes

The number of gametes produced by self-fertilization of a hybrid can be obtained by 2n where n is the number of traits for heterozygosity. In trihybrid n is 3, so the number of gametes produced by it is 8. A trihybrid for seed color, seed shape, and pod shape (YyRrIi) will produce YRI, YRi, YrI, Yri, yRI, yRi, yrI, yri.

The Punnett square will contain 64 possible unions of gametes.