Sexing mollusks by DNA


Feb 3, 2003
Hello. According to an article in Science News (Mar 7, 2004?):

Mammals with an XX set of chromosomes become female. Those with XY become male. The Y chromosome is much smaller than the X.

Birds with a ZZ set of chromosomes become male. Those with ZW become female. The W chromosome is much smaller than the Z.

My question:

Which chromosomes determine sex in a mollusk? Is it simple to see, as in birds and mammals, or does it depend on individual genes on one or several chromosomes? Is there a general rule for all mollusks, or do different species sex out differently?

Thank you. Mark Wood, Nanakuli, Hawaii.

Steve O'Shea

TONMO Supporter
Staff member
Nov 19, 2002
Mark, I feel terrible that I've not been able to respond to this query to date. I've been a little distracted at work of late.

I do have papers on cephalopod karyotypes, but I cannot remember who wrote them (and my literature colelction is organised by author, alphabetically, and is quite large). I searched today for the references in the most obvious places, but did not find them. I also spent an inordinate amount of time searching the web for phrases like 'karyotype Cephalopoda', 'karyotype squid', 'karyotype octopus', and did the same through the majority of electronic journals that I have access too, also searching cephbase. In each search I turned up zip.

I can see how frustrating this might be for you. There are papers on this subject matter, I know for sure, 100%; what I'll have to do is start at A and work my way to Z, and will do so this weekend to locate them; when I do I'll be able to post something online for you.

In the event anyone else finds something in the interim, please post away.


Colossal Squid
Nov 19, 2002
Hi I'm in the same boat as Steve, I have squid genetics papers but........!

I will have a hunt when I get some time :lol:

One thing I do know from bitter experience that squid DNA can be immensely difficult to extract. The tissues contain large quantities of mucopolysaccharides (slime!) which can inhibit precipitation of DNA :evil:

I believe a Russian (I think) researcher called Sokolov has gone some way to immproving this situation!

Jul 22, 2004

Yes, Sokolov wrote a paper called "An improved method for DNA isolation from mucopolysaccharide-rich molluscan tissues" (J. Moll. Stud. (2000), 66, 573-575). He didn't use Cephs for his study though... He used Polyplacophora, Gastropoda and Bivalvia...
Another paper concerning DNA-Extraction from molluscan tissue is Winnepenninckx et al. "Extraction of high molecular weight DNA from molluscs" (Trends Genet. 1993 Dec;9(12):407.)...
Octopus DNA was successfully extracted with the Chelex-Method (see "Sequence divergence of mitochondrial DNA indicates cryptic biodiversity in Octopus vulgaris and supports the taxonomic distinctiveness of Octopus mimus Cephalopoda; Octopodidae", Marine Biology (2000) 136: 29-35).

I am currently working with Sepia DNA (actually I am just starting) and I use the QiaGen Tissue Kit for DNA-Extraction... It seems to work well so far...