紅果蠅孤雌生殖的遺傳研究

Abstract

紅果蠅孤雌生殖的後代數遠低於有性生殖，且會行減數分裂產生單倍細胞，之後以只產生同結合型個體的配子重複為主要恢復二倍體的機制，因而導致遺傳變異降低。在這兩個不利條件之下，推測是兼性模式使孤雌生殖得以在自然界維持，因為有孤雌能力的雌蟲可以產生大量的有性生殖後代，且這些後代仍有行孤雌生殖的能力，所以遺傳變異可以進入孤雌生殖系統；再加上交尾後雌蟲仍可進行孤雌生殖，有助於保留孤雌生殖等位基因。經基因定位的實驗顯示，能否行孤雌生殖由一個主要的顯性遺傳因子控制，位於第二號染色體左臂 B1 D5 附近或其間；而後代數則受到許多數量性狀基因座的影響。有孤雌生殖能力的日本紅果蠅與臺灣烏來族群的親緣關係最接近，我們發現實驗室的烏來品系有行孤雌生殖的能力，論文中討論高比例的第二號染色體左臂的 B1 到 D5 區段逆位的異結合型和孤雌生殖長期保留在有性生殖品系中的關係。

Low fecundity and a very high percentage of gamete duplication mechanism which only generates homozygotes are two disadvantages of parthenogenetic Drosophila albomicans. Facultative mode may rescue parthenogenesis from these drawbacks. Females capable of parthenogenesis reproduce lots of offspring through sexual reproduction and those F1 females can also perform parthenogenesis. In addition both sexual reproduction and parthenogenesis are performed after mating. Therefore, parthenogenetic factors can be amplified and genetic variation can be reintroduced into this system. Genetic mapping revealed a major genetic element, may be located on 2L chromosomal arm, with dominant effect for parthenogenetic capability and several genes with additive effect for parthenogenetic fecundity. Parthenogenetic D. albomicans was discovered in Japan. The population was probably derived from Taiwan population for flies in Wulai were the phylogenetically closest. A sexual strain originated from Wulai, Taiwan in 1970 was found to be able to perform parthenogenesis. This strain carries high In(2L)B1D5 heterozygosity, which may be a reason why parthenogenesis can sustain after long-term sexual reproduction with limited individuals per generation.