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Dihybrid Crosses

Dihybrid Crosses. Figuring out the probability of passing on 2 separate genes at the same time. Monohybrid Cross. Looking at a single gene. H = widow’s peak h = no widow’s peak Cross Hh x Hh. Results = 75% Widow’s, 25% none. Dihybrid Cross.

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Dihybrid Crosses

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  1. Dihybrid Crosses Figuring out the probability of passing on 2 separate genes at the same time.

  2. Monohybrid Cross • Looking at a single gene. • H = widow’s peak • h = no widow’s peak Cross Hh x Hh Results = 75% Widow’s, 25% none

  3. Dihybrid Cross • A cross between two individuals looking at 2 different genes at the same time. • For example: • H = widow’s, h = none • L = long 2nd toe, l = short 2nd toe • Cross 2 people heterozygous for both HhLl x HhLl

  4. 1. Figure out Gametes Using FOIL method HhLl x HhLl • First • Outside • Inside • Last HL HL D/D Hl Hl D/r hL hL r/D hl hl r/r

  5. 2. Plug Gametes into outside of 16 box Punnett Square

  6. 3. Figure out the genotypes

  7. 4. Figure out phenotype #s • D/D – Widow/Long = 9 • D/r – Widow/Short = 3 • r/D – None/Long = 3 • r/r – None/Short = 1

  8. Pedigrees • Shows a pattern of inheritance in a family for a specific trait (phenotype) • Genotypes can usually be determined • Why would we want to use a pedigree in genetics?

  9. Track the occurrence of diseases such as: • Hemophilia– sex-linked recessive – causes person to bleed • Huntington’s– simple dominant – lethal allele – causes breakdown of the brain • Cystic fibrosis – 1/2500 – mucus accumulates (white North Amer.) • Tay-Sachs disease – lipids accumulate in CNS (Jewish)

  10. Huntington’s – Lethal Dominant

  11. Pedigree of Queen Victoria AKA: family tree Graphic representation of family inheritance. Pedigree Analysis

  12. The Symbols used:

  13. Inheritance patterns: • The disease is never passed from father to son. • Males are much more likely to be affected than females. • Trait or disease is typically passed from an affected grandfather, through his carrier daughters, to half of his grandsons. Sex-linked recessive • Examples: • Color-blindness • Duchenne Muscular Dystrophy

  14. Most Confusing Pedigree • I’m my own grandpa…

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