Mendels Dihybrid Crosses Dihybrid Cross crosses that involve

Mendel’s Dihybrid Crosses Dihybrid Cross • crosses that involve 2 traits 1. Mendel crossed round yellow peas (RRYY) with wrinkled green peas (rryy)

RRYY x rryy ry RY Rr. Yy ry Rr. Yy P 1 generation ry ry Rr. Yy F 1 generation RY Rr. Yy Rr. Yy

all were round and yellow phenotype genotype all were Rr. Yy

2. Next, Mendel crossed two F 1 plants. Rr. Yy x Rr. Yy RY Ry r. Y ry RY RRYy Rr. YY Rr. Yy Ry RRYy RRyy Rr. Yy Rryy F 2 generation r. Y Rr. Yy rr. YY rr. Yy ry Rr. Yy Rryy rr. Yy rryy

9/16 round yellow 3/16 round green 3/16 wrinkled yellow 1/16 wrinkled green phenotype

Law of Independent Assortment • Mendel found that alleles for different traits are inherited independently of each other • e. g. round doesn’t have to stay with yellow and green doesn’t have to stay with wrinkled

Summary of Mendel’s Principles 1. The inheritance of traits is determined by units called genes. 2. Genes are passed from parent to offspring. 3. When 2 forms (alleles) of a gene for a single trait exist, one may be dominant and the other recessive.

4. In sexually reproducing organisms, each adult has 2 copies of each gene – one from each parent. 5. The alleles for different genes segregate independently of one another.

Exceptions 1. Incomplete Dominance • one allele is NOT dominant over the other e. g. red flowers x white flowers = pink 2. Codominance • both alleles contribute to the phenotype e. g. in chickens, black and white feathers are co-dominant and produce speckled chickens

3. Multiple Alleles • many genes can have more than 2 alleles