Sex-biased Broods

As discussed here, chromosomes carrying RanGAP[Sd] cause haploid nuclei acquiring chromosomes carrying Rsp[s] to remain decondensed during spermatogenesis and, consequently, for the RanGAP[Sd]-bearing chromosomes to be inherited preferentially. The strength of this effect depends on the presence of gain-of-function mutations in the M(SD)E(SD) and St(SD) genes.

By moving SD components from their usual second chromosome positions to the X or Y chromosomes, one can generate males that produce predominantly X- or Y-bearing sperm.

Males producing mostly X-bearing sperm

Dp(2;Y)cb25-4 is a Y chromosome into which a segment of the second chromosome carrying Rsp[s] has been inserted. In the presence of RanGAP[Sd], spermatids inheriting this Y chromosome are less likely to produce functional sperm.

The following stock may be used to generate males producing mostly X-bearing sperm, but it requires some explanation.

The strength of the SD effect depends heavily on the relative number of copies of Rsp[s] and E(SD)[1]. Because this stock carries two copies of Rsp[s] and only a single copy of E(SD)[1], neither spermatids inheriting the Rsp[s]-bearing X chromosome (C(1;YL)19-3) nor spermatids inheriting the Rsp[s]-bearing Y chromosome (Dp(2;Y)cb25-4) will be completely eliminated. Males in this stock have reduced fertility, but they are fecund enough for the stock to survive.

In order to see strong elimination of Dp(2;Y)cb25-4 and strongly female-biased broods, males from this stock must be crossed to females from a RanGap[Sd] Rsp[i] E(SD)[1] stock to recover males carrying one copy of Rsp[s] and two copies of E(SD)[1]. The following stocks should work. (We have not tested these stocks to know which is the best choice.)

The following stock provides an alternative to stock 64331 above.

Males from this stock should be crossed to females from one of the SD stocks above. The Dp(2;Y)cb25-4, Rsp[s]/+; RanGAP[Sd] Rsp[i] E(SD)[1]/CyO male progeny (with relatively weak SD effects) should then be crossed to females from one of the SD stocks to produce Dp(2;Y)cb25-4, Rsp[s]/+; RanGAP[Sd] Rsp[i] E(SD)[1]/RanGAP[Sd] Rsp[i] E(SD)[1] males where the SD effect should be strong.

The advantage of using this stock is that it allows you to combine any two SD second chromosomes to maximize the sex bias. (Again, we have not tested combinations to know which produce the strongest female bias in progeny broods.)

Males producing mostly Y-bearing sperm

If you followed the description above for generating males that produce predominantly X-bearing sperm, you'll see immediately that an X chromosome carrying Rsp[s] can be used to generate males producing predominantly Y-bearing sperm. In fact, the same stocks can be used.

C(1;YL)19-3 is a Y chromosome in which the short arm (YS) has been replaced by X euchromatin and a large segment of X centric heterochromatin. A section of second chromosome centric heterochromatin including Rsp[s] is inserted in YL. In crosses, C(1;YL)19-3 segregates like a regular X chromosome.

Males carrying C(1;YL)19-3 with RanGAP[Sd] and two copies of E(SD)[1] will produce mostly Y-bearing sperm. As above, these males can be produced in two different ways. First, females from stock 64331 can be crossed to males from one of the following stocks: 64322, 64323 or 64324 to produce C(1;YL)19-3, y[1] w[1], Rsp[s]/Y; RanGAP[Sd] Rsp[i] E(SD)[1]/RanGAP[Sd] Rsp[i] E(SD)[1] males where the SD effect should be strong.

Alternatively, different combinations of SD-5, SD-72 and SD-Mad chromosomes from the table above can be combined with C(1;YL)19-3 in a series of crosses involving the stock below and relevant balancer stocks. There are lots of ways to do this and, if you've made it this far, you can probably figure it out without our help...

Related links   Segregation Distorter