I think that this section maybe don´t be accurately correct:
"This loss is masked under ordinary circumstances because each child has children with another member of the species, which contributes genes of her own. However, if that child is also one of only two children, then half of her parents' heterozygosity was lost. Thus, the third generation may receive from her mother some of the genes that her father did not receive from his parents. However, the net result is the same: 8 chromosomes of information from 4 grandparents were available to the second generation, but only 4 chromosomes of information from 2 parents is available to the third generation. Thus, heterozygosity is reduced in each generation."
Within a family this reasoning is ok. But genes that becomes extint in one specific family can stay in huge numbers in other members of the population. To genetic drift occurs, all the samples of one gene must, by chance, be not present within the new generation. In other words: the genes must be extinguished from the gene pool. The fluctuation of the frequencies cause sometimes genetic drift. The lower the population, the greater the probability of a gene becoming extinct therein.
Luiz Alexandre Silva 05:21, 26 May 2012 (PDT)