Training

1
(Chapter 2)
Predict the Phenotypic ratio
B bent pinky b straight pinky
F freckles f no freckles
BbFf X Bbff
Bb x bb BB, Bb, Bb, bb Bent straight 3/4
1/4
Ff x ff Ff, Ff, ff, ff Freckles no
freckles 1 /2 1/2
B/F B/f s/F
s/f 3/4x1/2 3/4x1/2 1/4x1/2 1/4x1/2
3/8 3/8 1/8 1/8 3
3 1
1 37.5 37.5
12.5 12.5
2
Dihybrid Testcross
3
Genotypic Probability

• Multiplication Rule when simultaneous events
  occur independently

Aa Bb Cc X Aa Bb Cc
What is probability of producing aa bb cc
offspring?
aa bb cc
1 x 4
1 x 4
1 4
1/64 (1.56) chance
4
Phenotypic Probability
Aa BB Cc DD X Aa Bb cc dd
What is probability of producing offspring
having all 4 dominant traits (A/B/C/D)?
A_ B_ C_ D_
3 x 4
4/4 1 x 1
2/4 1 x 2
4/4 1 1
3/8 (37.5) chance
5

• Multiplication (Product) Rule
• prob. A B prob. A x prob. B
• Aa X Aa parents want 2 children
• What is the probability of 1st offspring showing
  dominant trait
• the 2nd offspring showing the recessive trait

1 (3/4) x
2 (1/4)
AA, Aa, Aa, aa
3/16 (18.8) chance
Addition Rule prob. A or B prob. A prob.
B What is the probability of having 1 of 2
offspring showing the dominant trait and the
other showing the recessive trait
(event 1 x event 2) or (event 1 x event
2) A_ aa or aa
A_
( 3/4 x 1/4 ) (1/4 x
3/4) 3/16
3/16
6/16 3/8 (37.5) chance
6
Human Pedigrees
7
Human Trait Chart
Ability Ability no abil A_ aa
Aa
Cleft Cleft Cleft C_ C_
C_
flat flat flat aa aa
aa
8
Dominantly Inherited Trait
Huntingtons Disease HD/HD or HD/hd normal
nervous system hd/hd
hd
hd/hd
HD/__
hd/hd
hd/hd
hd/hd
hd/hd
HD/hd
HD/hd
HD/hd
HD/hd
HD/hd
HD/hd
HD/hd
HD/hd
hd/hd
hd/hd
hd/hd
hd/hd
hd/hd
Every affected person has at least one affected
parent