Hi,
Microsatellites can be used to determine kinship, the genetic status of a population, among other things, but do not give any information of sex of the individual. It is in the non-coding region of DNA.

Your right but i was thinking out loud, that if a genome ca be sequenced, and specific regions shown to be present/ absent or have specific intragenic spacer regions/ repeating motifs then microsats may be possibe. It certainly wouldn't need to be coding DNA, makes no real difference...

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Scratch that, it makes some difference... but then it depends how much we trust concepts of selection, and neutral selection. Interesting problem though.

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I guess I'll have to show my ignorance here...

How does all this factor into sexing if there is no genetic link to the different sexes of chelonians.

Ed

Im thinking there are no sex chromosomes, but perhaps could still be differences on other chromosomes....

Worth a thought, but would need the genome sequencing... Just thinking out loud.

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lol leave you guys to this one

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home sweet home

Along your lines of thought there would have to be differences between the sexes given tail length, shell shape... but as you say it would require a genome for the species and if I'm not mistaken they either have just come up with the human genome or they are close to it after how many years of research. I think chelonians a pretty far down the list.

ed

Genome sequencing will not give the answer. The mechanism of TSD is still poorly understood. If the temperature during the certain stage of embryonic development is the only factor that changes the sex of the organism (except other artificial means such as hormone treatment), then there will be no difference between the geomes of male and female.

What is different, thus determining which gonad will form, is the expression of genes (which gene is on or off). The gene expression changes with different temperatures, in the case of TSD.

Aren't the physical differences between the sexes expressed by different genes? I would think they would have to be. I'm sure there is a way of telling but we have not reached that level... yet.

Ed

There are two stages of sexual determination. The first (primary sexual determination) is the formation of gonads. the secondary sexual determination affects phenotype besides gonads, such as different body size, shape, more/less hair....

in species with chromosomal sexual determination, the primary SD is controlled by different genes, for example, in mammals, Y chromosome contains a gene that code for a testis determining factor, which makes the gonad into a testis, not an ovary. And of course, only men have Y chromosome. Without that gene, the gonad becomes an ovary by default.

The secondary SD is controlled by gonads. The gonads produce sex hormones that determines the secondary sexual characteristics.
However, the difference is mostly in the amount of sex hormone that is produced. For example, we women produce both testosterone and estrogen, only a lot more estrogen and not much testosterone, in men, it's vice versa. Both male and female have genes that code for those sex hormones. It is just regulated differently.

In TSD species, the primary sexual determination is dependent on the temperature. Males and females have the same set of genes, but the expression of those genes are controlled by temperature. Only way to tell the difference is to look at the gene product, protein and such, to see which gene is expressed where and when.

Hope I didn't bore you with this.