Download PowerPoint

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts
no text concepts found
Transcript
THE GENETIC BASIS OF EVOLUTIONARY CHANGE
1. Simple, discrete traits
2. Continuous traits
Evolution: A change in gene frequency
GG
BB
GB
1 locus, 2 alleles
Co-dominant
Heterozygote detectable
Phenotypes
GG
3 (.25)
BB
3 (.25)
GB
6 (.50)
12 (1.0)
What are the frequencies
of the three phenotypes
in this population?
Phenotypes
Genotypes
GG
3
3 (.25)
BB
3
3 (.25)
GB
6
6 (.25)
12
12 (1.0)
What are the frequencies
of the three genotypes
in this population?
Phenotypes
Genotypes
GG
3
3
BB
3
3
GB
6
6
12
12
What are the frequencies
of the two alleles or genes
in this population?
How many G’s? 12 (50%)
How many B’s? 12 (50%)
Hardy-Weinberg
p = frequency of one of the alleles
(the dominant one, if there is dominance)
q = frequency of the other allele
(recessive, if there is recessiveness)
p + q = 1.0
p (G) = 0.5
q (B) = 0.5
0.5 + 0.5
=
1.0
The relationship between gene frequencies
and genotype frequencies
p + q
=
1.0
GG + GB + BB = 1.0
p2 + 2pq + q2 = 1.0
.25 + .50 + .25 = 1.0
Red heads is caused by the recessive gene r
What are the phenotype frequencies of
people with red and blue heads?
Red: .25
Blue: .75
Genotype frequencies?
RR
Rr
rr: 25
How do we find the
frequencies for RR and Rr?
The relationship between gene frequencies
and genotype frequencies
p + q
=
1.0
GG + GB + BB = 1.0
p2 + 2pq + q2 = 1.0
.25 + .50 + .25 = 1.0
If you know what q2, or rr, is, you can solve the others
Red heads is caused by the recessive gene r
What are the phenotype frequencies of
people with red and blue heads?
Red: .25
Blue: .75
Genotype frequencies?
RR: .25
Rr: .50
rr: .25
r =
= .5
.25= .5
R = 1-r
p2 + 2pq + q2 = 1.0
Gene and genotype frequencies will be the same
every generation if the population is
1. Large
2. Randomly mating
3. Not receiving migrants
4. Not undergoing selection
IN “HARDY-WEINERG EQUILIBRIUM”
Factors that can change gene frequencies:
1. Selection
2. Drift
3. Mutation
4. Migration
Factors that can change gene frequencies:
1. Selection: Differential reproductive success
or reproductive FITNESS
Red leaves fewer offspring relative to Blue
time
Blue produces more offpring relative to Red
time
Factors that can change gene frequencies:
1. Selection
2. Drift: In small populations, “sampling error”
chance fluctuations in reproduction
DRIFT
time
Founder effect
Time and space
Factors that can change gene frequencies:
1. Selection
2. Drift
3. Mutation : recurrent and directional
Recurrent mutation of R --------> r
time
Factors that can change gene frequencies:
1. Selection
2. Drift
3. Mutation
4. Migration: introduction of genes from outside
the population.
time
THE GENETIC BASIS OF EVOLUTIONARY CHANGE
1. Simple, discrete traits
2. Continuous traits
Example of disruptive selection:
Sexual dimorphism
Example of Directional selection:
cranial capacity
Example of balancing selection:
Birth weight
Related documents