PROVIDENCE, R.I. [Brown University] For a bunch of inanimate chemical compounds, the nucleic and amino acids caught up in the infamous "selfish" segregation distorter (SD) saga have put on quite a soap opera for biologists since the phenomenon was discovered in fruit flies 50 years ago. A new study, a highlight in the March issue of the journal Genetics, provides the latest plot twist.
In TV listings the series would be described this way: "A gene exploits a rival gene's excesses, sabotaging any sperm that bear the rival's chromosome." The listing is not an exaggeration except for ascribing malicious intent to strings of biochemicals. When male flies make their sperm, the SD gene (call it "A") manages to rig meiosis the specialized cell division that makes sex cells so that maturing sperm that bear chromosomes with the susceptible allele (call that one "a") end up defective and discarded. They never even leave the testes.
It is murder of a sort. Similar selfish systems occur in mammals, including humans.
In the Genetics study conducted at Brown University, scientists uncover new clues about how the SD gene might be gaming the system against "a." It's a plot so fiendish, only an aggregation of genetic bases could evolve it. It also deepens biologists' understanding of an instance in which life violates a fundamental balance predicted by the father of genetics, Gregor Mendel.
"Mendel's first law is that different alleles of a gene will segregate," said Robert Reeenan, professor of biology and the study's senior author. "If we have two alleles big A and little a then Mendel says 50 percent of the sperm at random will get the big A and 50 percent of the sperm will get the little a. But some SD (A) alleles are so strong they pretty much kill off all the non-SD (a) chromosomes.
"This is a real cheater, a real stinker," Reenan said. "Most genes, like most people, are good upstanding citizens, but some
|Contact: David Orenstein|