Keywords: fertility variation, status number, group

coancestry, inbreeding, gene diversity, reference

population

Gene diversity and inbreeding over five generations

are simulated considering fertility variations and

population sizes in finite populations. Gene

diversity of seeds is influenced by differences in

fertility among parents and their relatedness. The

overall relatedness can be described as group

coancestry. The fertility is expressed as a

standardised measure of fertility differences among

individuals. Fertility variation causes faster

accumulation of relatedness and reduces the

effective number (status number) of the seed crop.

Status number (Ns) is defined as half the inverse of

group coancestry. Group coancestry is the

probability that two genes in a gene pool are

identical by descent, and it can also be interpreted as

an average of relatedness or as a lost of gene

diversity. Group coancestry of the present

generation is the expected inbreeding (F) of the

following if individuals mate at random and if they

are equally fertile. Inbreeding, group coancestry,

status number and gene diversity are all relative to a

conceptional reference population with an infinite

number of unrelated and non-inbred individuals. A

small status number means a reduced gene diversity

of seeds, because Ns expresses the accumulated

genetic drift from the same reference population to

which the concepts inbreeding and coancestry refer.

The build-up of coancestry and inbreeding during

successive generations is potentially a major

problem when dealing with small populations (such

the breeding populations). The consequences can be

predicted, evaluated and monitored in this study.

on this decline has been studied. Gene diversity

decreased faster as the fertility variation increased.

But the effect of fertility variation on gene diversity

was not linear.

Predictions over five generations shown that group

coancestry and inbreeding accumulated fast, and the

status number and variance effective population size

decreased remarkably in the first generation shifts.

The accumulation of inbreeding and group

coancestry was faster and higher when the fertility

variation was larger. The loss of gene diversity was

proportional to the fertility variation and to the size

of the population. The gene diversity was

maintained high when provided the breeding

population size was reasonable. Long term breeding

programs that use small population sizes and low

status effective numbers may lead to a loss of gene

diversity and do not provide a sustainable long-term

breeding strategy. This study helps us to understand

how large numbers are required to maintain

reasonable gene diversity.