Genetic Crosses

by Alla Tue Aug 19, 2008 4:18 am

MonkeyNacho wrote:i have a question that i've now been trying to think of for a couple of hours, but my text book only explains half of what i need.

For this, (Corn kernels), the phenotypes and genotypes are: Su = Starchy, su = sugary, R = Purple, r = yellow

The question is: A cross between two pure breeding (Homozygous) corn plants was set up to produce an F1 generation. Complete:

PARENTS: Phenotype - ........ X .........
Genotpye - .........X ..........

what i don't understnd, however, is if i use two Hoomozygous dominant parents, or recessive, or 1 of each? because it sayd two pure breeding ones, but i don't know if that means 2 of the same, or different pure bred corn plants...any suggestions?

First, pure breeding parents means parents that produce progeny of the parental phenotype when self-fertilized - homozygous. The goal of this cross is to produce a homogeneous population of heterozygous dihybrids (SsRr - starchy/purple in this case). You have a choice: you can breed SSRR x ssrr (starchy/purple to sugary/yellow) or SSrr x ssRR (starchy/yellow to sugary/purple). Both crosses would have the same result. However, usually dihybrids are produced from the cross of two plants that are different from wild type in one trait each -- that would mean the second choice - SSrr x ssRR (starchy/yellow to sugary/purple).

Good luck!