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Dihybrid cross Tutorial
- 1. Dihybrid Cross Crossing two different traits Hair length and eye color
- 2. Hair Length* • HH – Hh short hair (dominant trait) • hh long hair (recessive trait) * Yes I realize that this is not an actual heritable trait. Just go with it.
- 3. Eye Color • RR – Rr black eyes (dominant) • rr red eyes (recessive)
- 4. The Parents • Both parents are heterozygous for both traits. • Hh Rr
- 5. H h R r FOIL the parents H R rhH R rh Use the concept you learned in math class.
- 6. H h R r FOIL the parents H R rh HR r h
- 7. H h R r FOIL the parents H R rhHR r h These are the different combinations of the two traits that the parents’ sex cells will contain.
- 8. Since both the parents had the same genotype, we only needed to foil one parent. This rarely happens. Now we place each parent’s alleles on the Punnett square. I usually place the father on the top and the mother on the side. They will be color coded so that you can tell the difference.
- 10. HR HR Hr hR hr Hr hR hr We copy one parent’s alleles into the boxes.
- 11. HR HR Hr hR hr Hr hR hr H R H R H R H R H r H r H r H r h R h R h R h R h r h r h r h r (These are the alleles from the parent on top)
- 12. HR HR Hr hR hr Hr hR hr H R H R H R H R H r H r H r H r h R h R h R h R h r h r h r h r We copy the other parent’s alleles into the boxes.
- 13. HR HR Hr hR hr Hr hR hr HHRR HHRr HhRR HhRr HHRr HHrr HhRr Hhrr HhRR HhRr hhRR hhRr HhRr Hhrr hhRr hhrr Here are both parents’ alleles. Notice it does not matter which parent is first; only that the dom. allele is in front and that each trait is together.
- 14. What are the kids going to look like? • HHRR • HHRr • HhRR • HhRr • HHrr • Hhrr • hhRR • hhRr • hhrr Short hair, black eyes Short hair, red eyes Long hair, black eyes Long hair, red eyes Genotypes Phenotypes
- 15. HR HR Hr hR hr Hr hR hr HHRR HHRr HhRR HhRr HHRr HHrr HhRr Hhrr HhRR HhRr hhRR hhRr HhRr Hhrr hhRr hhrr Do you see the pattern?
- 16. What are the kids going to look like? • HHRR • HHRr • HhRR • HhRr • HHrr • Hhrr • hhRR • hhRr • hhrr Short hair, black eyes 9 Short hair, red eyes 3 Long hair, black eyes 3 Long hair, red eyes 1 Genotypes Phenotypes