Dihybrid Crosses

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# Dihybrid Crosses - PowerPoint PPT Presentation

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

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
• 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

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
• D/D – Widow/Long = 9
• D/r – Widow/Short = 3
• r/D – None/Long = 3
• r/r – None/Short = 1
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?

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 of Queen Victoria

AKA: family tree

Graphic representation of family inheritance.

### Pedigree Analysis

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.

• Examples:
• Color-blindness
• Duchenne Muscular Dystrophy
Most Confusing Pedigree
• I’m my own grandpa…