Platypus sex is XXXXX-rated - VeggieBoards

Forum Jump: 
Thread Tools
#1 Old 10-24-2004, 03:45 PM
schu's Avatar
Join Date: Jun 2003
Posts: 1,111

Platypus sex is XXXXX-rated

18:00 24 October 04

The weird and wonderful duck-billed platypus just got even more weird and more wonderful.

Platypuses are famous for laying eggs yet producing milk, having a bird-like bill and a skeleton with reptilian features. Now it turns out that the mammal has an equally eye-catching way of deciding its sex, according to a study by Frank Grützner and Jenny Graves at the Australian National University in Canberra, and colleagues.

In most mammals, including humans, sex is decided by the X and Y chromosomes: two Xs create a female, while XY creates a male. In birds, the system is similar: ZW makes for a female, while ZZ makes for a male.

But in platypuses, XXXXXXXXXX creates a female, while XYXYXYXYXY creates a male. In other words, rather than a single chromosome pair, platypuses have ten-chromosome chains that determine their sex.

The researchers worked out the make-up of platypus sex chromosomes by using fluorescent markers to stain chromosomes in platypus cells before examining them under a microscope.

The researchers also found that when sperm is produced by male platypuses, the chromosomes in the chain are precisely distributed to form XXXXX-bearing sperm and YYYYY-bearing sperm. When an XXXXX-bearing sperm fertilises an egg it produces a female platypus. YYYYY-bearing sperm would produce a male.

Howler monkeys

It is certainly unusual. You only need one sex-determining gene on one chromosome on a chromosome pair. Its intriguing why it evolved such a complex system, says cytogeneticist Jon Martin at Melbourne University.

Very few other mammals are known to have more than two sex chromosomes. The black howler monkey, for example, has four sex chromosomes - the most known until the platypus finding. But the platypus is outstanding, as usual, says Grützner.

The extra chromosomes in the monkey are probably due to a hiccup in evolution whereby non-sex chromosomes mutated to become similar to the sex chromosomes.

This similarity would then cause both pairs to be passed on during reproduction. A similar process might have led to the ten-chromosome system in the platypus, though researchers admit to being stumped.

Mammals and birds

Another intriguing discovery from the study is that one end of the platypuses chromosome chain shares similarities with mammalian sex chromosomes, while the other end shares characteristics with the sex chromosomes of birds.

The platypus X1 chromosome has 11 genes that are found on all mammalian X chromosomes. The X5 carries a gene called DMRT1, which is also found on the Z chromosome in birds.

But although many people believe that DMRT1 will turn out to be the key sex-determining gene in birds, Grützner cautions that there is no evidence that it plays a similar role in the platypus.

The way in which chromosomes determine sex in mammals and birds was thought to have evolved independently after the two classes diverged 300 million years ago.

"But this links the two systems together and raises the issue of whether the ancestral mammal had a sex chromosome system similar to birds, says Grützner.

Journal reference: Nature (DOI 10.1038/nature03021)
schu is offline  
Sponsored Links
#2 Old 10-24-2004, 03:53 PM
synergy's Avatar
Join Date: Mar 2004
Posts: 6,887
That is really messed up.

Lokah Samastah Sukhino Bhavanto

'May everyone everywhere be happy
May the whole world be joyous'
synergy is offline  
#3 Old 10-27-2004, 10:29 AM
gguru1's Avatar
Join Date: May 2004
Posts: 166
Does this have anything to do with the fact that the males have a two pronged penis?

gguru1 is offline  
#4 Old 10-27-2004, 10:38 AM
Formerbaboon's Avatar
Join Date: May 2004
Posts: 6,201
Why is it so messed up? Its only natural, right?
Formerbaboon is offline  
#5 Old 10-27-2004, 03:45 PM
GhostUser's Avatar
Join Date: Oct 2010
Posts: 0
Originally Posted by gguru1 View Post

Does this have anything to do with the fact that the males have a two pronged penis?

Okay, now I'm REALLY scared to check my DNA...

The Rev
GhostUser is offline  
#6 Old 10-27-2004, 08:24 PM
superjane's Avatar
Join Date: Apr 2003
Posts: 828
platypuses (or is it platypi) are so cool! Has anyone seen one in RL?
superjane is offline  
#7 Old 10-28-2004, 04:45 AM
Chook's Avatar
Join Date: Apr 2003
Posts: 330
Originally Posted by superjane View Post

Has anyone seen one in RL?

Yep. There are some in the creek near my Mum's house.
Chook is offline  

Quick Reply

Register Now

In order to be able to post messages on the VeggieBoards forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page

Forum Jump: 

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off