Dihybrid Crosses Dihybrid Crosses Looks at 2 different

Dihybrid Crosses

Dihybrid Crosses • Looks at 2 different traits at the same time. • For example, one cross would be used to cross the traits, pea plant height and pea flower color. T = tall P = purple t = short p = white

Genotypes and Phenotypes Height T = tall t = short Color P = purple p = white • A homozygous dominant for height, heterozygous for color Tall, Purple TTPp = ____ Phenotype = _______ • A heterozygous for height, homozygous recessive Ttpp Tall, White = ____ Phenotype = _______ • A homozygous recessive for height, homozygous dominant for color tt. PP Short, Purple = ____ Phenotype = ________

Height T = tall t = short Color P = purple p = white Let’s try one Crossing a heterozygous tall (Tt)-heterozygous purple (Pp) with a heterozygous tall (Tt)heterozygous purple (Pp)…. . 1. Determine the genotypes. = Tt. Pp x Tt. Pp 2. FOIL Method – to determine allele combinations (First, Outer, Inner, Last) example: Tt. Pp First = TP, Outer = Tp, Inner = t. P, Last = tp 3. Make your boxes – place ** combinations along top and side.

Tt. Pp x Tt. Pp • A Punnett square for a dihybrid cross has 4 boxes on each side for a total of 16 boxes. • Bring down the alleles, putting the same letters together. • Remember ALWAYS write the dominant allele first but keep the same trait’s alleles together! • You have to do “FOIL” for each individual that is mating.

Genotypic and Phenotypic Ratios TP Genotypic: __**_ TTPP Tp t. P tp TP ** ** Tp ** ** ** __**_ TTPp __**_ Tt. PP __**_ TTpp __**_ Tt. Pp __**_ Ttpp t. P __**_ tt. Pp __**_ ttpp tp

Genotypic and Phenotypic Ratios TP Phenotypic: __**___ Tall , Purple Tp t. P tp TP TTPp Tt. PP Tt. Pp Tp TTPp TTpp Tt. Pp Ttpp Tt. PP Tt. Pp tt. PP tt. Pp Ttpp tt. Pp ttpp __**___ short, Purple __**___ Tall, white __**___ short , white ** In a dihybrid cross, crossing two t. P heterozygous organisms ALWAYS results in a ** tp ratio!