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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

Dihybrid Crosses

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

monohybrid cross
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
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

1 figure out gametes using foil method
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

4 figure out phenotype s
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
pedigrees
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?
slide9

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)
pedigree analysis

Pedigree of Queen Victoria

AKA: family tree

Graphic representation of family inheritance.

Pedigree Analysis

inheritance patterns
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
most confusing pedigree
Most Confusing Pedigree
  • I’m my own grandpa…