Principles of Plant Genetics and Breeding

118 CHAPTER 7
B C
D E
A B
C
E
A
I
I
D
G
B
D
Figure 7.4 The inbreeding coefficient (F) may be calculated by counting the number of arrows that connect the
individual through one parent back to the common ancestor and back again to the other parent and applying the formula
in the figure.
AA × aa
Aa
Generation AA Aa aa
F 1
F 2
F 3
F 4
0%
25
100%
25% 25%
50
12.5 12.5
0%
37.5 25 37.5
6.25 6.25
43.75 12.5 43.75
3.125 3.125
F5 46.875 6.25 46.875
(a) (b)
25
=
=
A
I
C
E
A B
C
E
I
D
G
F I = ( 1 /2) 5 (1 + F A) + ( 1 /2) 5 (1 + F B)
% homozygosity
100
Self-fertilization
=
+
1 /2
1 /2
A B
C
E
B
D
1 /2 (1 + Fn)
A
I
I
C
E
F I = ( 1 /2) 5 (1 + F A)
50
0 4 8
Generation
12 16
Figure 7.5 Increase in percentage of homozygosity under various systems of inbreeding. (a) Selfing reduces
heterozygosity by 50% of what existed at the previous generation. (b) The approach to homozygosity is most rapid under
self-fertilization.
Full sibs
Half sibs
D
G
1 /2
1 /2