Dihybrid Punnett Squares You are a product of your family and your environment.

Review: Monohybrid Cros Autosomal Dominant/Recessive inheritance Predicting one trait at a time –Mono=one

Dihybrid Worksheet Autosomal Dominant/Recessive Inheritance Dealing with two traits at a time –Di-hybrid(“di”= two) –Diagram to right: Round vs wrinkled Green vs yellow

Two phenotypic traits Hair color H=dark hair h= light hair Eye Color B=Brownb=blue

Mendel’s Law of Independent Assortment Traits are caused by genes on different chromosomes Ex. Gg Yy –Can form sperm or eggs that are GY, Gy, gY, or gy –Sorting of DNA into gametes is random of other chromosomes

What type of gametes? Person homozygous for dark hair and dark eyes Genotype: HHBB Gametes: only HB HH BB HB

Heterozygous for one trait What about a person heterozygous for dark hair and homozygous dominant for eye color Genotype: HhBB Gametes: HB or hB Hh BB HB hB HB hB

Heterozygous for both traits What gametes will a person heterozygous for both traits produce? Genotype: HhBb Gametes: HB, Hb, hB, hb Hh Bb Hb hb HB hB

Dihybrid Worksheet Step 1 Step 1: Determine genotypes of both parents –One parent is homozygous dominant for both traits … Genotype: HHBB –…other parent is heterozygous for both traits. Genotype: HhBb

Step 2: List all possible gametes Parent 1 genotype: HHBB –HB Parent 2 genotype: HhBb –HB –Hb –hB –Hb –Your punnett square will be one by four squares long

Step 3: Draw punnett squares Dimensions depend on parent’s gametes No longer simply two by two Parent’s gametes are 1 and 4 so punnett square will be 1 by 4

Step 4: Take one parent and list possible gametes on appropiate side –Parent one had 1 possible gamete production(HB) HB

Step 5 Take other parent and list possible gametes along punnett squares –Parent 2 has 4 possible gametes(HB, Hb, hB, hb) HB Hb hB hb

Step 6 Carry out punnett squares and fill them in –Dihybrid is two traits: four alleles HB Hb hB hb HHBB HHBb HhBB HhBb

Step 7 Write genotype ratios Genotype:1 HHBB:1HHBb:1HhBB:1 HhBb HB Hb hB hb HHBB HHBb HhBB HhBb

Step 7 Write the phenotype ratios F1 phenotype: All dark hair/brown eyes HB Hb hB hb HHBB HHBb HhBB HhBb