Haldane's rule, which states that the heterogametic sex is preferentially afflicted if
one of hybrid sexes is sterile or inviable, is a general pattern in all animals that possess
sex chromosomes. The hybrid sterility component of this rule is especially important
because hybrid sterility is involved in the onset of postzygotic isolation. Accumulating
evidence on the fast evolution of individual sex genes have stimulated us to hypothesize
that the fast evolution of sex genes may be the force underlying the excess of hybrid
heterogametic sterility. This study tests the evolutionary patterns of sex genes in
comparison to non-sex genes, as a general group. The divergences between a group of 19
sex genes and 20 non-sex genes from X chromosome were compared between D.
melanogaster, D. mauritiana, D. simulans, and D. sechellia using PCR-RFLP. Within
species polymorphism data were also obtained for D. simulans and D. mauritiana. The
results show a significantly higher divergence for sex genes than non-sex genes, while a
comparable level of intraspecific polymorphism was revealed in both groups. Among the
sex gene group, genes related to male reproduction appear to evolve faster than femalereproductive
genes. The evolution of both sex and non-sex genes conforms to the neutral
theory under Tajima's test and HKA test. The faster evolution of sex genes supports the
fast-sex theory as an explanation for the hybrid sterility component of Haldane's rule.
Localization of some examples of hybrid sterility genes is crucial to ultimately untangle the genetics of hybrid sterility. The car region of D. mauritiana, which has been shown to harbor genes that confer full effect of hybrid sterility in the D. simulans genetic background, was introgressed into the D. simulans genome by continuous backcrosses.
Recombination mapping analysis, taking advantage of molecular markers, revealed that
at least two regions are capable of causing hybrid sterility in this species group. The
phenotypes of hybrid testes were examined during the backcross process. / Thesis / Master of Science (MSc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22475 |
| Date | 01 1900 |
| Creators | Xu, Li |
| Contributors | Singh, R.S, Biology |
| Source Sets | McMaster University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
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