Chapter 10.2 – Punnett Squares I.Punnett Squares – a shorthand way of finding the expected proportions of possible genotypes in the offspring of a cross A.Monohybrid Cross - 1 trait 1.2 boxes tall by 2 boxes wide 2.each parent creates 2 kinds of gametes for 1 trait

3.Example:  tall plant (TT) x short plant (tt)T t t Possible Phenotypes: 100% Tall Possible Genotypes:100% Tt Tt

B.Dihybrid Cross – 2 traits 1.4 boxes tall by 4 boxes wide 2.each parent creates 4 kinds of gametes for 2 traits 3.Example: Guinea pig alleles  S = short hair, s = long hair  B = black hair, b = brown hair 2 guinea pigs, each SsBb, are mated with each other

Use F.O.I.L. to create 4 gamete choices F=First (2 different letters), O=Outer, I=Inner, L=Last S s B b Gamete choices:SB, Sb, sB, sb

SB Sb sB sb SB Sb sB sb Possible Phenotypes:  Short, Black Hair (S_B_)9/16  Short, Brown Hair (S_bb)3/16  Long, Black Hair (ssB_)3/16  Long, Brown Hair (ssbb)1/16 SSBBSSBbSsBBSsBb SSBbSSbbSsBbSsbb SsBBSsBbssBBssBb SsBbSsbbssBbssbb