6.6: Why is genetic diversity important? (2024)

There are three main reasons to maintain genetic diversity, not simply because it has a relation with inbreeding.

1. An important reason is that genetic diversity allows for flexibility in a population. If circumstances change, different genotypes may be more suitable and selection pressure will change. If the alleles required to adapt to the new circumstances are no longer present, or only at very low frequency, then adaptation of the population will be very difficult. Potentially with devastating consequences.

2. Inbreeding (increase in homozygosity) causes inbreeding depression. Inbred animals tend to be less healthy, live shorter, and have a reduced reproductive capacity.

3. Related to that: reduced genetic diversity results in increased homozygosity, also of alleles that have deleterious effects. More inbred animals means more animals that suffer from monogenic recessive disorders.

Inbreeding results in increased homozygosity, so also in more homozygous recessives. The negative result of that can be expressed as the performance of animals that are inbred, compared to animals that are not inbred, or as the change in phenotype given 1% increase in inbreeding level. For example, a study on Dutch Shetlandpony stallions showed a clear effect of inbreeding level on sperm quality features. Within the live fraction, inbreeding had a decreasing effect on the percentage normal sperm, and an increasing effect on the percentage with abnormal head (van Eldik et al., 2006. Theriogenology 65:1159-1170). There have been no studies on the effect of sperm quality on the fertilization results, but it is likely there will be a certain minimum quality necessary for successful breeding.