 | Prep for USMLE |
| Forum | Resources | New Posts | Register | Login | » |
|
| Author | 3 Posts | |||||||||||||||||||||||||
|
jimmyhe
Forum Newbie Topics: 5 Posts: 24 |
Hi to All, Could anybody explain the concept of Mosaicism with example? Thanks
|
Prep4USMLE.com
|
Advertisement
|
|
Ahab
| Forum Senior Topics: 9 Posts: 227
Random inactivation of X chromosome in any somatic cell with more than one chromosome (usually XX but also in XXY kleinfelters syn) Occurs at late blastocyst stage. Explains why females do not have double the levels of X chr generated protein products wrt males, i.e factor VIII, dystrophin etc. Identified from Barr body in nucleus from buccal smear. Termed mosaicism because if you look at a tiled mosaic you will see that despite looking at a complete image, on closer examination each tile is made up of one and only one colour. X inactivation is not complete, there is up to 16 genes that escape inactivation, those that share homology with Y chromosomes. Neither is X inactivation always random. If the X chr contains a deletion it is usually the defective chromosome that will be inactivated more often. However if the X abnormality is a balanced translocation then it is the normal one which is inactivated, explaining the occurances of X recessive diseases in females. Germ cells do not undergo inactivation. Finally, as you statistics people will know 50% is the normal amount of inactivation (equal amounts of both X chrs total), however because each inactivation is an independant event not related to the others it is possible for the inactivation to be skewed (60:40) and if the inactivation excessively occurs on the good X chr, then the defective one will be present more possible expressing some X disease phenotypes (haemophilia) Hope that makes some bit of sense
|
jimmyhe
| Forum Newbie Topics: 5 Posts: 24
Ahab, than you so much. Your explaination help a lot.
|
|
| | |||||||||||||||
|
This thread is closed, so you cannot post a reply.
 Similar forum topicsmosaicism Mosaicism? Turner mosaicism | Related resources |
Advertise | Support | Premium | Contact |
Your Privacy Choices