Linked from
The 13 pages that link to Heterozygosity, each with the reason it gives.
Genetic driftRelated: Loss of alleles through drift often lowers this measure of genetic variation.
Genetic diversityRelated: It measures within-individual variation at selected genetic locations.
Self-pollinationRelated: Selfing tends to reduce heterozygosity across generations.
Lethal alleleRelated: A heterozygote may survive while transmitting a recessive lethal allele.