Dihybrid Crosses

1. Dihybrid Crosses When observing 2 traits **UNLINKED** i.e. located on different xsomes

2. Dihybrid Crosses • A dihybrid cross occurs when two traits are being examined at the same time, but follow the law of segregation • Independent of each other OR • Located on different xsomes • Need to list possible gametes created from the P1 generation, and then compete a cross that lists all of the possibilities in a Punnett square

3. Predicting Gametes and Drawing Punnett Square • Dihybrid Punnett Square is always 4 x 4 (16 possibilities in the F1)

4. Predicting Gametes – list all possibilities – PUNNET SQUARE • MMRR – MR, MR, MR, MR (or just MR) • MmRR – MR, mR • mmRR - mR • MMRr – MR, Mr • MmRr – MR, Mr, mR, mr • MMrr - Mr • Mmrr – Mr, mr Want to know some SHORTCUTS?!?!?!?!

5. Hints • Write out all possible gametes that can be formed • Create Punnett square using ONLY gametes that are NOT repeated • Punnett square can be 1 to 16 squares • Ex MMRR x mmrr • Possible Gametes MR • Possible Gametes mr • Punnett square • OUTCOME = 100% same genotype and phenotype

6. Hints • For 16 square punnett square ONLY count out phenotypes • Dominant, Dominant • Dominant, Recessive • Recessive, Dominant • Recessive, Recessive In a heterozygous cross = 9:3:3:1

7. WORK TIME!! SOMEONE PLEASE GET THIS “LIME” OFF MY HEAD!!!