Naked Scientists Podcast

The Naked Scientists: Science Radio & Science Podcasts

Subscribe via itunes,yahoo or google < Previous Show | Next Show >
2nd Jul 2006

Sex Chromosomes, Genetics and Food Webs


Phil Rosenberg

Chris Smith

Breaking things down to the building blocks of life this week is Dr Mark Ross from the Sanger Institute in Cambridge, who discusses the evolution of sex chromosomes, genetics and genomes; Dr Michael Traugott from the University of Innsbruck describes a novel way of using genetics to find out who is eating whom in underground food webs; and Derek Thorne gets fruity with Lucy Wheatley extracting DNA from a kiwi...

 

Listen NowDownload as MP3 Podcast
Transcript Go back Vote for Us

Digg Thisfacebookdel.icio.usNetscapeRedditFarkStumbleuponNewsvineYahoo! My WebFurlMagnoliaSquidoo

Science News

 

Life on Other Planets Comes Closer To Home

The holy grail of finding extraterrestrial life has been the discovery of an Earth-sized planet with just the right temperature for liquid water to exist on the surface...
 

Magnet Knocks Migraines on The Head

Researchers in America at the Ohio State University Medical Centre, led by neurologist Yousef Mohammad, have found that a quick zap to the head with a magnet can stave off a migraine attack. Character...

Questions

 

Is there any scientific reason why a key suspended from a length of string held over food always seems to indicate correctly whether I can eat a particular food? If I eat anything containing MSG (monosodiumglutamate) in any form, I get a very severe migraine. If it rotates clockwise then the food is taboo, but if it rotates anticlockwise then the food is ok for me to eat. I really can't believe that this is true.


 

I tend to get awful headaches that fall under the migraine classification but I notice that they're weather related. Why is it that weather should have these effects?


 

How cold is it in outer space and how do you protect satellites from extreme cold?


 

Why do we assume that life on other planets would be a carbon-based Homo erectus type of being that breathes oxygen? Could it not breathe hydrogen or methane or be based on a different element?


 

If as a human I share 98% of my genes with a chimpanzee and 60% of my genes with a banana, how come I only share 50% of my genes with my own daughter?


 

Why do people go bald?


 

I'd like to hear about recessive genes and why they say that blondes and ginger people have more of these genes and will become extinct. Why will the genes only kick in now and not before and have there been genes in the past that have timed out? Is it possible for genes like green hair to start up and replace them?


 

Why is it, that despite all this talk of evolution going on, humans have not evolved for the last 4000 years?


 

Do scientists have any understanding of the mechanisms that skills, that animals such as humans, learn and pass to their offspring via their genetic code?


Interviews

 

Science Update - Ancient Supernovae and Ducks

Chelsea Wald and Bob Hirshon from AAAS, the science society
 

Sex Chromosomes And X-linked Diseases

Dr Mark Ross, the Sanger Institute, Cambridge
 

Who Eats Whom in The Undergrowth

Dr Michael Traugott, University of Innsbruck and University of Cardiff

Kitchen Science

 

How to extract DNA from a kiwi fruit


You've heard about DNA, but have you ever seen any? This week Derek and Lucy extract DNA from Kiwi fruit using just simple kitchen items.

Fact or Fiction

The call of the humpback whale is louder than Concorde
TrueTrue
The longest python in captivity is 10 feet long
TrueTrue
If you fell down a long tunnel drilled through the earth - assuming terminal velocity of 200 kilometres per hour was maintained throughout the trip - it would take you over 2 days to reach the other side of the planet
TrueTrue
A chicken can lay 1000 eggs during its lifetime
TrueTrue
The average person in England can expect to live for 2.5 billion seconds
TrueTrue

Sex Chromosomes, Genetics and Food Webs - More about this podcast

X & Y Chromosomes

Figure 1: The larger X (on the right) and Y (left) chromosomes magnified 15000 times by an electron microscope.

Ever wondered why there is an 'x' in 'sex'? Or indeed why you are the sex you are? The answer lies in your DNA… This week on the Naked Scientists Dr Mark Ross, an Investigator at the Wellcome Trust Sanger Institute (part of the International Human Genome Sequencing Consortium), will be on the show to tell us about all about the X chromosome. Mark Ross has co-authored publications on the map and sequence of the human genome as a whole, and led the team that sequenced and analysed the human X chromosome. His major research interests lie in studying the sequence for clues to the evolution and biology of what he considers the most interesting of human chromosomes.straight-forward chromosomes, but at one point X became touched by magic and developed special powers that allowed it to determine sex. Chromosomes are made up of DNA, which is a chain of chemical building blocks known as nucleotides. There are four types of nucleotide; adenine (A), cytosine (C), guanine (G) and thymine (T). Last year the X-chromosome's DNA sequence was published by a team led by Dr Mark Ross. 115 million As, Ts, Cs and Gs later the X chromosome is giving clues to how sex chromosomes evolved, and the role of X-linked genes in human disease.

Humans have 23 pairs of chromosomes; 22 of those come in identical pairs, this allows them to swap DNA with their partner. One pair of chromosomes has non-identical partners, they are X and Y and they don't like to share. Once upon a time, (roughly 300 million years ago, to be a bit more specific) there lived an animal which was the ancestor of mammals, birds and reptiles. Sometime later (a bit less specific as this is still only a theory) mammals and birds went their separate evolutionary ways, each with a different pair of chromosomes responsible for determining sex. In mammals this pair was X and Y, in birds it was W and Z.

 

The Sanger Institute's Mark Ross

Figure 2: The Sanger Institute's Mark Ross, who is trying to answer fundamental questions about where the X chromosome came from, and how the genes encoded within it are controlled.

For mammals the sex determination trigger was pulled by the emergence of the Y-chromosome SRY gene - this is the master switch in male development. Over time most of the Y chromosome's DNA lost the ability swap with X, without a partner it could use as a template to repair damage, Y has gradually become a shrunken stump and lost most of its DNA. The X chromosome has 1100 genes and Y only 76. This can be seen in figure 1. See there is a reason your mother told you to share your toys!

Generation X:
Mark Ross is comparing the human chromosome sequence with the X chromosome of other mammals. From this study is seems that the X chromosome has gained pieces of DNA at various stages of mammalian evolution, the leading change occurred when a large region from another chromosome was added during the evolution of the placental mammals. Other changes have been more subtle. Chunks of DNA have been acquired by the X and Y chromosomes simultaneously, so there would have been two active copies. Over time the Y chromosome segment has decayed and the X copies have been recruited into X chromosome inactivation gradually.

X chromosome inactivation:
X spent so much time evolving into the ultimate cool chromosome, so why is there a need for inactivation? The answer lies in the role of X and Y in mammalian sex determination; females are XX and males are XY. To prevent females with their two X chromosomes receiving a double dose of male gene products, one of the X chromosomes is shut down early in the development of the female embryo. Originally it was thought that the inactivated human X would be completely inert, however using the genome data from the Sanger Institute and its collaborators; this is not the case at all. Looking at activity levels of hundreds of genes on the inactive X, it was found that about 15% escape from inactivation. A further 10% of supposedly inactive genes are actually active in some women but not in others. Of all the 40 women used in the study, each had a unique pattern of gene activity.

So why do some genes become inactive whilst others choose to carry on as normal and what does this mean for the individual? At the moment it is too early to say, preliminary studies however, show that inactivation escapees may underlie the effects of sex chromosome anomalies. Mark is currently investigating the differences between regions of X chromosome inactivation and regions of escape. He wants to find out whether the genes that escape form domains or whether they escape on a gene by gene basis.



Naked Scientists Science Radio Show HomeNaked Scientists Science Radio Show Home Who are The Naked ScientistsWho are The Naked Scientists Information about Naked ScientistsInformation about Naked Scientists
Naked Scientists PodcastNaked Scientists Podcast Ask the Naked Scientists PodcastAsk the Naked Scientists Podcast Question of the Week PodcastQuestion of the Week Podcast
Naked Science ArticlesNaked Science Articles Experiments to do at HomeExperiments to do at Home Science Discussion ForumScience Discussion Forum
Science News StoriesScience News Stories Answers to Science QuestionsAnswers to Science Questions Interviews with Famous ScientistsInterviews with Famous Scientists

Click here for the Naked Scientists PODCAST

The contents of this site are © The Naked Scientists® 2000-2008. The Naked Scientists® and Naked Science® are registered trademarks.