Goal #3: Dihybrid Crosses

I. Law of Independent Assortment - alleles for different characteristics are distributed to gametes independent of each other

A. Mendel tested two of his pea plant traits: seed color and shape a. dominant – yellow and smooth (SSYY) b. recessive – green and wrinkled (ssyy) Question he asked: Must a round seed be yellow?

B. Mendel’s Methods: P 1 : SSYY x ssyy F 1 genotype: SsYy (all heterozygous) F 1 phenotype: smooth and yellow He crossed F1 generation and found alleles that were not present in either parent. (i.e. green and wrinkled) If there is dominance for one trait in an organism, are all the organism’s traits dominant? X

Example: –Black/Brown hair is dominant over blonde –Brown eyes are dominant over blue You may have black hair, AND blue eyes. C. Each characteristic is carried independently.

IV. Constructing Dihybrid Crosses A. crosses that will involve two traits instead of one B. 16 boxes

P 1 : SsYy x SsYy (heterozygous round and yellow) Alleles: SY, Sy, sY, sy (you match each letter up with another)

Genes on different chromosomes assort independently, because they are on different chromosomes; but what about genes on the same chromosome?

C#7: Dihybrid Crosses Worksheet – handing out DUE TUESDAY! Extra Credit: Construct a trihybrid cross with 3 pea plant characteristics. Be sure to set up P1, F1 genotypes and phenotypes the way we discussed! Due Wednesday! Due: Monday January 24th

Trihybrid Cross