Cheetah Genetic Diversity — MHC Genes & Disease Resistance
GED Science Practice — Reading scientific passages, evidence & research comparison
Read the passage
Scientists have examined the genetic history of a large group of cheetahs and have found that there was a significant decrease in the genetic diversity of the cheetah species about 10,000 years ago. Scientists found that, even in unrelated groups of cheetahs, individual cheetahs had 99% of the same alleles. By comparison, in a genetically diverse population, even closely related individuals contain only 80% of the same alleles. Genetic diversity is important to the survival of a species, and scientists worry that a disease that cheetahs are not resistant to could decimate the population.
Major histocompatibility complex (MHC) genes are used by the body to identify self from non-self and direct the immune system to attack non-self particles. Invading bacteria and viruses do not contain the same MHC genes and therefore are attacked by the immune system. Within a population, a high diversity of MHC genes protects the population from attack by disease. In a highly diverse population, it is likely that at least some individuals will contain an allele that identifies a new disease as non-self and can direct the immune system to destroy it.
In 1985, research by Stephen O'Brien reported that skin grafts from cheetahs in a zoo in Oregon were accepted by cheetahs in Africa. Skin grafts, like other organ donations, must be between individuals that have the same MHC factors. If any of the genetic factors are different, then the immune system of the individual receiving the organ will identify the organ as non-self and the body will attack the donated organ as if it were a foreign organism such as a virus or bacterium. The conclusion from O'Brien's research was that cheetah MHC genes are as alike as those of identical twins.
More recent research by Simone Sommer took a much more comprehensive approach to examining the genes of a large sample of wild cheetahs. Sommer's research determined how many alleles are present on two different types of MHC genes in approximately 150 cheetahs. Sommer was able to show that the variation in some MHC genes was higher than previously thought. The variation in MHC genes in cheetahs is still smaller than that for other big cat species but appears to be sufficient to allow the populations to identify a wide variety of foreign particles.
GED questions from this passage
Sommer's research concludes that cheetahs have sufficient genetic diversity to respond to common diseases, but may still be at risk of new diseases.
Q1: Which statement from the passage supports this conclusion?
Q2: Why is the conclusion about gene variation among cheetahs from Sommer's research more valid than the conclusion from O'Brien's research?
Cheetah genetic diversity — animated diagram
Cheetahs share 99% of their alleles — compared to 80% even in closely related individuals of diverse species