Help with genetics and punnett squares?

Question

Pure Polka Dot petunias crossed with zebra-stripped petunias result in 100% checker board offspring. If a checkerboard male petunia and checkerboard female are crossed , how many of their 1000 offspring will be: A. Checkers B. PPD's C. zebras

Answer 1

Okay, to solve this, you need to assign a letter to the alleles.  Say PP is the polka dot (pure, so both letters are alike, or homozygous).  The zebras would be pp (also pure, so the letters alike).  But when they're crossed, each parent would contribute a gene, so you'd have all offspring be Pp (heterozygous, since the alleles are different).  

To find out your ratio of types on the cross between 2 Pp petunias, set up a Punnett square:

___|_P_|_p_|

_P_|.PP.|.Pp.|

_p_|.Pp.|.pp.|

So your results are 1 PP (1/4), 2 Pp (1/2), and 1 pp (1/4) of the 4 results.

With 1000 offspring, 1/4 or 250 would be PP, 1/2 or 500 would be Pp, and 1/4 or 250 would be pp.