Population Significance of High Frequency Recessive Lethals in Drosophila albomicans

紅果蠅（Drosophila albomicans）高頻率隱性致死因子之族群意義

張慧羽(Hwei-Yu Chang) ； 藍淑芬(Shu-Fen Lan) ； 林飛棧(Fei-Jann Lin)

《Zoological Studies》 35卷2期 (1996/04) Pp. 138-145

摘要

紅果蠅（Drosophila albomicans）第二對染色體左臂具有高頻率逆位的B1D5區段，也同時擁有較高的致死因子頻率。這個事實讓我們開始質疑以往認為染色體逆位有扣住一組組彼此配合良好的基因之功能。本文提出一個“陷阱”假說來解釋為何族群中會同時存在高隱性致死因子頻率與高異結合逆位頻率。本文報告烏來和關仔嶺兩地的紅果蠅自然族群之染色體逆位In(2L)B1D5的平均異結合型比率高達0.64，而隱性致死因子的頻率則高達0.44，估算確實位於逆位區段的隱性致死因子的頻率為0.37。由於B1D5區段僅佔第二對染色體的四分之一，相較於其它果蠅種類，其頻率顯然是高出許多。根據陷阱假說，隱性致死因子的累積是造成異結合型頻率增高的原因，而異結合型的自由分離（Principle of segregation）與配子的重組所導致的遺傳負荷（Genetic load）才是染色體逆位異結合型優勢（Heterosis）的真正原因。高隱性致死因子頻率與高染色體逆位頻率的共存符合這個假說的預期。

關鍵字

染色體逆位 ； 酯酶 ； 致死因子頻率 ； 族群遺傳

並列摘要

The high frequency of recessive lethals on a segment of the 2nd chromosome with high inversion frequency challenged a previously suggested role of chromosome inversions in maintaining sets of coadapted genes in natural populations of Drosophila albomicans. A hypothesis to account for the high frequency of both recessive lethals and the inversion heterozygosity is then proposed. After an investigation of natural populations from Wulai and Kuantzuling, Taiwan, it was found that In(2L)B1D5 heterozygosity reached 0.46 and the recessive lethal frequency related to it reached 0.44. The estimated recessive lethal frequency within this inversion region was 0.37. Since (2L)Bps in D. albomicans comprises only a quarter of the 2nd chromosome, the lethal frequency in this chromosomal segment of D. albomicans is indeed much higher compared to other Drosophila species. The coexistence of high lethality and high inversion heterozygosity is in accordance with our prediction of the trapping effect of inversions for recessive deleterious alleles. The accumulation of recessive lethals causes an increase of inversion heterozygosity, and the genetic load due to the principle of segregation seems to be the real reason for inversion heterosis.

並列關鍵字

Chromosomal inversion ； Esterases ； Lethality ； Population genetics