Basic concepts of population genetics - Bioversity International

Locus A
Locus B
Locus D
… with a dominant marker (continued)
Locus A
Locus B
Locus D
M 1 2 3 4 5 6 7 8 9 10
M 1 2 3 4 5 6 7 8 9 10
1 0 1 1 0 1 1 1 1 1
0 1 0 0 0 1 0 0 1 0
1 1 1 1 0 1 1 0 1 1
Copyright: IPGRI and Cornell University, 2003 Population genetics 25
25
Individuals
Here we have an example similar to that in the previous slide but with 10 individuals and three
segregating loci (A, B, and D). (M = size marker.)
Non-segregating bands (monomorphic) are not scored and thus are not included in the analysis.
Below, we see the table with calculations of genotype and allele frequencies:
Locus
s
A
B
D
Genotypes
Genotype freq. (exp.)
Number of indivs.
Genotype freq. (obs.)
Genotypes
Genotype freq. (exp.)
Number of indivs.
Genotype freq. (obs.)
Genotypes
Number of indivs.
Genotype freq. (obs.)
Data analysis
A 1 _
p 2 + 2pq
8
P 1 = 0.8
B 1 _
p 2 + 2pq
3
P 1 = 0.3
D 1 _
8
P 1 = 0.8
A 2 A 2
B 2 B 2
D 2 D 2
2
P 2 = 0.2
Total
Total
10
1
Allele freq.
0.55
0.16
q 1
2
p2 Genotype freq. (exp.) + 2pq
p q
q 2
2
P 2 = 0.2
q 2
7
P 2 = 0.7
Total
1
10
1
1
10
1
p
p
0.55
We cannot distinguish heterozygotes, but we can estimate the expected number of
heterozygotes in a population. For example, if sample size = 1000, then:
For locus A, no. expected heterozygotes = 2pqN = 2(0.55)(0.45)(1000) = 495
For locus B, no. expected heterozygotes = 2pqN = 2(0.16)(0.84)(1000) = 269
and so on ...
q
0.45
q
0.84
0.45