Molecular Cytogenetics of Reproductive Failure in Gorillas

Modern methods of genetic analysis have focused attention on what have been called “genomic diseases.” A growing number of chromosomal syndromes associated with severe medical problems in humans have been shown to be caused by predisposition to genomic rearrangements. The same conditions can be expected to exist for other species, when more is learned about their biology and medicine. Such predisposition to rearrangements is a general phenomenon, but its basis is described in detail in relatively few species.

For many endangered species, especially the bonobo, chimpanzee, and gorilla, that are most closely related to humans and are also highly endangered, risks of genetic disease can become a significant factor for population survival. Maka, a gorilla born at the San Diego Zoo, is notable for his reduced stature and accompanying deletion of a large portion of his third chromosome. Although Maka’s dwarfism can be accommodated by the members of his social group, he is not an appropriate candidate for breeding subsequent generations of gorillas in managed care.

Although researchers in the Genetics Division of CRES know considerable details about Maka’s chromosomal problems, additional knowledge is required in order to estimate whether his parents are at risk of producing additional growth-retarded individuals and whether, for natural populations of gorillas in the wild, the same genetic risk factors that produced Maka are in evidence. Without further study, researchers are unable to assess the extent to which chromosomal risk factors may influence fertility in captive gorilla populations. There are considerable data to infer that, within western lowland gorillas, genetic subpopulations exist. If interbreeding between gorilla subpopulations produces increased risk of chromosomal errors, then it is important to identify the causes and adapt population management to minimize impacts before the risks are spread throughout the population.

The management of captive gorilla populations may benefit from molecular cytogenetic analyses to evaluate the risks for rearrangements already known to occur (such as Maka’s) as well as to assist in diagnosis of suspected chromosomal disorders. With the availability of a gorilla BAC library constructed from one of the female gorillas at the Wild Animal Park and the ability to compare fine structure chromosomal organization utilizing fluorescence in situ hybridization (FISH), gorilla populations can be assessed for reproductive failure risk factors in new and more powerful ways.

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