Multi-trait inheritance Dihybrid Crosses Multi-trait inheritance

Mendel’s further experiments Mendel’s monohybrid crosses were based on one characteristic controlled by one gene such as seed shape (round or wrinkled) in a pea plant. He then went on to ask: “What happens when more than one characteristic is involved in a cross?”

Crossing two traits He focused on two characteristics: Seed shape - (Round - R, and Wrinkled – r) Seed colour - (Yellow - Y, and Green - y) He crosses two plants that were heterozygous for seed shape (Rr) and seed colour (Yy) in what we now know as a Dihybrid Cross.

P generation The first figure shows a cross between to homozygous parent plants that produce plants that are heterozygous for these two traits. RrYy RrYy RrYy RrYy

Possible Combinations A heterozygous individual for two characteristics will produce four possible gametes. R r Y y RY Ry rY ry

The Law of Independent Assortment Each allele is independent of the other and no two alleles are linked. In other words, the inheritance of seed shape has no influence on the inheritance of seed colour. A dihybryd cross can be treated as two separate monohybrid crosses.

Two trait cross between heterozygous seeds RRYY RRYy RrYY RrYy RRYy RRyy RrYy Rryy rrYy RrYY RrYy rrYY RrYy Rryy rrYy rryy

F2 Genotypes 1/16 RRYY 1/8 Rryy 1/8 RRYy 1/8 rrYy 1/8 RrYY 1/16 rryy

3/16 - Wrinkled ,Yellow Seed F2 Phenotypes 9/16 - Round, Yellow Seed 3/16 - Round, Green Seed 3/16 - Wrinkled ,Yellow Seed 1/16 - Wrinkled, Green Seed