Dihybrid Cross Notes

1. Dihybrid Cross Notes By Mr. W. Wright

2. Monohybrid cross 1 • We Learned that a _______________ is crossing two organisms and looking at __ trait. • Mono = • A ____________ is crossing two organisms and looking at ___ traits. • Di = 1 dihybrid cross 2 2

3. Example Dark hair Dark eyes light hair light eyes H= allele for ______ B= allele for _______ 1st Trait- 2nd Trait- h= allele for _______ b= allele for _______ Consider the cross between to parents with the following genotypes Parents: ________x __________ We draw a punnett square. HhBb HhBb

4. H h B H b B h b H B b B B B H H B H H h H B h H b B H b b h H B h H b H B b H b H H b b h h B B H h B h h B h b B H b B h B h h b b h b b H h B H h b h h B b b

5. H=Dark Hair LH=Light Hair E=Dark Eyes LE= Light Eyes H, E: H, LE: LH, E: LH, LE Phenotype Ratio: Genotype Ratio: Leave blank As you can see, usually two parents that are heterozygous for both traits are the hardest punnett squares 1 3 9 3

6. Example 2: Freckles Dimples • A male with freckles and dimples mates with a female with freckles but no dimples; what are the possible offspring. F=allele for________ D=allele for _______ 1st Trait 2nd Trait f= allele for________ d=allele for_______ A Possible genotype cross may yield is … A punnett square may look like… Parent phenotype: No Freckles No Dimples FFDdXFFdd Freckles with dimples Freckles with no dimples

7. F F F F D d D d F d F d d F D d d d F F D F F F F d F d d F d F D F d F F D F F F d d d F F F d F d F d F d D F d F D F d d F F d F D d F d d F d d F F F D F d

8. F=Freckles NF=No Freckles D=Dimples ND= No dimples F, D: F, ND: NF, D: NF, ND Phenotype Ratio: Genotype Ratio: Leave blank 0 8 0 8