This doesn't instantly make sense to me.
Lets say you have 100 people from a subpopulation who were sequenced and aligned to a reference genome. For certain variants, people were either homozygous for the loss-of-function alternate allele, or homozygous for the reference allele.
This indicates consanguineous practices within the population. However, I'm told that this also indicates that the alternate allele is recessive and that if it were dominant, there would be very few heterozygotes due to selective pressure, and individuals would not reach a breeding age. This doesn't make sense to me. If it were recessive, there would be an excess of heterozygotes, and if it were dominant, there would be very few heterozygotes, but if there are no heterozygotes, that indicates that it's recessive?
I also fail to see how either condition can be determined in this case.