Feeds

What are chromosome abnormalities and how often do they occur?

A dip into the gene pool

Build a business case: developing custom apps

Also in this week's column:

What are chromosome abnormalities and how often do they occur?

Asked by Lynn Davis of Casper, Wyoming

Each of our chromosomes has a specific and proper structure and colour. Together, they form a distinct pattern called the human karyotype. We have 46 chromosomes (23 from each parent). But biology being biology, there are variations in reproduction resulting in abnormalities in the karyotype of an individual. A very few are beneficial, most are harmless, a few are catastrophic.

A major chromosome abnormality (MCA) accounts for half of all spontaneous human abortions. A MCA occurs in about one in every 100 to 200 births. Recent medical diagnostic techniques can now detect many MCAs long before the child is born. They do this by analysing the patient's blood under a microscope. MCAs take one of five forms.

  1. In duplication, instead of the normal two, the individual has three copies of the chromosome in every cell of their body (trisomic). Most trisomics result in a spontaneous abortion - but not always. Trisomy-21 (Down's Syndrome) occurs 1.5 times in every 1,000 births. The individual has three copies of chromosome 21. Trisomy-18 (Edward's Syndrome) occurs three times in every 10,000 births. The individual has three copies of chromosome 18. Trisomy-13 (Patau's Syndrome) occurs two times in every 10,000 births. The individual has three copies of chromosome 13.
  2. In deletion, a piece of chromosome may go missing. The missing piece is usually from the end of the chromosome, but can be missing from the middle as well. The types of symptoms as well as their severity will vary depending upon the size and location of the deletion. Deletion syndromes occur at a frequency of about one in every 16,000 births. In Wolf-Hirschhorn Syndrome (occurring in one in every 50,000 births) the abnormality occurs on chromosome 4. In Cri-du-Chat Syndrome (occurring in one in every 50,000 births), the abnormality occurs on chromosome 5.
  3. In translocation, a whole or a piece of one chromosome becomes attached to another.
  4. In inversion, a portion of the chromosome breaks off, turns upside down, and reattaches.
  5. In rings, a portion of the chromosome breaks off and forms a circle, with or without loss of genetic information. For these last three forms, there is an alteration in the pattern of genetic information.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au

Boost IT visibility and business value

More from The Register

next story
Just TWO climate committee MPs contradict IPCC: The two with SCIENCE degrees
'Greenhouse effect is real, but as for the rest of it ...'
Asteroid's DINO KILLING SPREE just bad luck – boffins
Sauricide WASN'T inevitable, reckon scientists
Flamewars in SPAAACE: cooler fires hint at energy efficiency
Experiment aboard ISS shows we should all chill out for cleaner engines
Brit amateur payload set to complete full circle around PLANET EARTH
Ultralight solar radio tracker in glorious 25,000km almost-space odyssey
NASA Mars rover FINALLY equals 1973 Soviet benchmark
Yet to surpass ancient Greek one, however
Famous 'Dish' radio telescope to be emptied in budget crisis: CSIRO
Radio astronomy suffering to protect Square Kilometre Array
BEST BATTERY EVER: All lithium, all the time, plus a dash of carbon nano-stuff
We have found the Holy Grail (of batteries) - boffins
prev story

Whitepapers

Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Why and how to choose the right cloud vendor
The benefits of cloud-based storage in your processes. Eliminate onsite, disk-based backup and archiving in favor of cloud-based data protection.
The Essential Guide to IT Transformation
ServiceNow discusses three IT transformations that can help CIO's automate IT services to transform IT and the enterprise.
Maximize storage efficiency across the enterprise
The HP StoreOnce backup solution offers highly flexible, centrally managed, and highly efficient data protection for any enterprise.