Hall B G
Genetics. 1980 Dec;96(4):1007-17. doi: 10.1093/genetics/96.4.1007.
Evolution of lactose utilization via the ebg system of Escherichia coli requires both structural gene (ebgA) and regulatory gene (ebgR) mutations. Because evolution of new metabolic functions in diploids might be subject to constraints not present in haploid organisms, merodiploid strains carrying a wild-type and an evolved ebgA allele, or a wild-type and an evolved ebgR allele were constructed. I show that heterozygosity at ebgA does not significantly affect the selective advantage of the evolved ebgA allele; whereas heterozygosity at ebgR eliminates the selective advantage of the evolved ebgR allele. Is is suggested that, in diploid organisms, evolution of new functions for systems under negative control would be very difficult.
通过大肠杆菌的ebg系统利用乳糖的进化需要结构基因（ebgA）和调控基因（ebgR）的突变。由于二倍体中新代谢功能的进化可能受到单倍体生物中不存在的限制，构建了携带野生型和进化型ebgA等位基因，或野生型和进化型ebgR等位基因的部分二倍体菌株。我发现ebgA的杂合性不会显著影响进化型ebgA等位基因的选择优势；而ebgR的杂合性则消除了进化型ebgR等位基因的选择优势。这表明，在二倍体生物中，负调控系统新功能的进化将非常困难。
