托福阅读练习材料:Fatherless Honeybees

　　蜜蜂的社会有哪些特殊之处?今天的新托福考试阅读练习资料中我们就要了解这方面的信息。

　　How male honeybees can be without fathers? The reason lies in what’s called a haploidiploid system of sex determination. Approximately one-fifth of the animal kingdom, including ants and wasps, use this system. What it boils down to is that males are the result of unfertilized eggs whereas females are born from fertilized eggs.

　　But in bees there is an added complication since there is a gene that determines whether a bee will be male or female. It’s all in the numbers. Here’s how it works.

　　A scientist isolated a gene called CSD, or Complimentary Sex Determiner. There are 19 different versions of this particular gene. It doesn’t matter which one of these 19 versions a male inherits from his mother; he’s going to be male because of the fact that he has only one of these CSD genes.

　　Accordingly, a female becomes a female because she has two CSD genes, except for one catch. And that catch is a bee in the bonnet of bee breeders.

　　Honeybee breeders often inbreed their bees in order to ensure desired traits. However, when bees are inbred it’s possible for fertilized eggs to end up with two copies of the same version of the CSD gene. The result is that the fertilized eggs would normally develop into workers or a new queen, develop into sterilized males.

　　Worker bees sense these sterile males when they’re still larvae, and they kill them. Before you know it, your honeybee colony has died out. The good news is that now that scientists understand more about how sex is determined among honeybees, they may discover solutions to this problem.