Genetics of Complex Traits: Quantitative Genetics - PowerPoint PPT Presentation

1 / 29
About This Presentation
Title:

Genetics of Complex Traits: Quantitative Genetics

Description:

Pink. Pink. Lt Pink. Lt Pink. white. All Pink. AaBb. x. AaBb. F1: aabb. white. x. AABB. red. P: 1 Red: 4 Lt Red: 6 Pink: 4 Lt Pink: 1 white ... – PowerPoint PPT presentation

Number of Views:618
Avg rating:3.0/5.0
Slides: 30
Provided by: KimHu9
Category:

less

Transcript and Presenter's Notes

Title: Genetics of Complex Traits: Quantitative Genetics


1
Genetics of Complex TraitsQuantitative Genetics
2
Genetic Variation
Discrete Variation (presence/absence of tail)
  • Continuous Variation (height)

3
Quantitative Genetics
  • Polygenic
  • Environmental influences
  • Have continuous (not discrete) distributions
  • Can be measured on a quantitative scale

Height Weight Athletic ability Risk of heart
disease Risk of diabetes Risk of cancer
4
Intermediate dominance additive gene action
Partial dominance
Discrete distribution
5
Red
Pink
Lt Red
Lt Red
Lt Red
Pink
Pink
Lt Pink
Pink
Lt Pink
Pink
Lt Red
Lt Pink
white
Lt Pink
Pink
1 Red 4 Lt Red 6 Pink 4 Lt Pink 1 white
6
Two additive genes discrete phenotypic
distribution
7
Color of wheat kernels three additive genes
aabbcc AABBCC
AaBbCC
8
Frequency Distribution of Height of the Band
mean68 inches
9
Properties of distributions
n 160
Mean 68 inches
Variance
9.5 in2
10
(No Transcript)
11
Types of Variance
  • Phenotypic variance total variance of the
    population, includes variation from genes and
    from the environment
  • Genetic variance the variance that is due to
    variation among individuals in the alleles that
    they have, excludes environmentally-caused
    variation

12
Phenotypic Variance
Mean 68 in
Var 9.5 in2
Phenotypic variance Genetic variance Environ.
variance VP
VG VE
13
Phenotypic variance Genetic variance Environ.
variance VP
VG VE
Genetic variance Additive variance Dominance
Variance VG VA
VD
VP VA VD VE
14
Additive and Dominance Effects (No Environmental
Effects)
15
Mean 18.5 cm
Var 1.333 cm2
VP VA VD VE
1.333
1.0
0.333
0
16
VP 1.333 cm2 VA
1.0 VD 0.333 VE
0
17
Heritability
VP VA VD VE
1.0
Broad-sense heritability H2 VG/VP
0.75
Narrow-sense heritability h2 VA/VP
18
Uses of heritability
  • The degree to which offspring resemble their
    parents is determined by the narrow-sense
    heritability h2
  • The efficacy of natural and artificial selection
    is also determined by h2

19
(No Transcript)
20
h2 1
VA/VP 1
h2 0
VA/VP 0
21
Efficacy of artificial selection size of
Labradors
22
Breeders Question
  • Q A horse breeder wants to win the Kentucky
    Derby. If she breeds her mare to a really fast
    stallion, how likely is it that the colt will be
    faster than all the other three-year-olds when it
    runs in the Derby?

A It depends on the heritability of running
speed
23
Breeders Equation
  • R h2 S
  • S Selection differential
  • difference between selected parents and the
    population as a whole (within a generation)
  • R response to selection
  • difference between selected offspring and the
    unselected population (across generations)

24
Breeders Equation
  • R h2 S
  • A dog breeder chooses his largest dogs to breed
    together. The average height of the breed is 60
    cm (at the shoulder), and the dogs he chooses to
    breed average 70 cm tall.
  • He knows from previous work that the heritability
    of height is 0.5.
  • How big can he expect the offspring to be?

0.5 10cm 5cm
R h2 S
25
Breeders Equation
  • R h2 S 0.5 10 cm 5 cm
  • If the response to selection is 5 cm, he can
    expect his puppies to grow to be
  • 60 cm 5 cm 65 cm tall

26
Exactly the same equation can be used to
understand natural selection!
27
Efficacy of natural selectionDarwins finches
28
If large bills are favored in drought years, what
effect will an El Nino year have on the
population?
h2 0.8
29
R h2 S
  • Birds that survive the drought have bills that
    are 2 mm deeper (on average) than the population
    mean.
  • Q What will happen to the average bill depth in
    the next generation?
Write a Comment
User Comments (0)
About PowerShow.com