more info
http://en.wikipedia.org/wiki/Punnett_square
Main article:
Dihybrid cross
More complicated crosses can be made by looking at two or more genes. The Punnett square works, however, only if the genes are
independent of each other, which means that having a particular allele of gene A does not alter the probability of possessing an allele of gene B. This is equivalent to stating that the genes are not
linked, so that the two genes do not tend to sort together during meiosis.
The following example illustrates a
dihybrid cross between two heterozygous pea plants.
R represents the dominant allele for shape (round), while
r represents the recessive allele (wrinkled).
A represents the dominant allele for color (yellow), while
a represents the recessive allele (green). If each plant has the genotype
RrAa, and since the alleles for shape and color genes are independent, then they can produce four types of gametes with all possible combinations:
RA,
Ra,
rA, and
ra.
RARarAra
RARRAARRAaRrAARrAa
RaRRAaRRaaRrAaRraa
rARrAARrAarrAArrAa
raRrAaRraarrAarraa
remember x = y & all that stuff we learned back in HS
it helps in a small sort of way when dealing with breeding