chapter4 Change of gene frequency in small populations- The non-idealized population.ppt

Chapter 4
Change of gene frequency in small populations
- The non-idealized population
Effective population size
Effective number of breeding individuals that would give rise to the same variance of gene frequency or rate of inbreeding, when they bred in the manner of the idealized population.
All conclusions drawn for the idealized population can be applied for any real populations, if the actual population size is replaced by the effective population size.
The effective population size can be derived from the actual population size, when the breeding structure is known
Effective population size
Excluding self-fertilization:
Excluding sib-mating:
Unequal number of males and females:
(twice the harmonic mean)
Effective population size
Unequal numbers in essive generations:
Non-random variation of family size:
when variance of family sizes are the same for both sexes
when it is different
Effective population size
Equal number of individuals selected for breeding and no variation in family size
equal numbers of males and female
unequal numbers
Overlapping generations
L = generation interval,NT = number of individuals survived in the population
E = average age at death
Pedigreed populations
Inbreeding coefficient of an individual
Coancestry or coefficient of kinship
Coancsetry of two individuals: probability of two gametes taken at random, one from each, carrying IBD alleles
The inbreeding coefficient of an individual is equal to the coancestry of its two parents.
Basic rule
Generalized pedigree:
A  B C  D
P  Q
X
Coancestry of close relatives
Self:
Offspring and parent:
Full sibs:
Half sibs:
A and B are parents of X, A and C are parents of Y
Regular system of inbreeding
The same mating system is applied in all generations
All individuals in the same generation have the same inbreeding coefficient
Often used to produce inbred lines
Types:
Close inbreeding
Repeated backcross
Intercross after crossing
Close inbreeding
Self-fertilization: