#2 I post this twice, please don\'t duplicate answer I need two different views.

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#2

I post this twice, please don't duplicate answer I need two different views. Thanks

PLEASE, PLEASE, PLEASE, FOLLOW THE INSTRUCTOR. I DONT NEED JUST SOMETHING, I NEED YOU TO ANSWER WHAT I NEED. PLEASE DONT ANSWER IF YOU CANT DO EXACTLY I NEED. ALSO, PLEASE DO NOT COPY FROM ANY WEBSITE, IT HAS TO BE YOUR OWN WORD.

1. CHOOSE ONE OF TOPIC I LISTED

2.WHY YOU CHOOSE THIS PARTICULAR TOPIC

3. INCLUDE YOUR REPUTABLE SOURCE

4. REFERENCE

Hi All - this week you will be learning about chromosomes. I would like you to please write a paragraph about a topic related to what we are learning in class (please include your reputable source (0.5 pt) to earn full credit). Please include WHY (1 pt) you chose your topic to earn full credit - this way, duplicate topics will be allowed. Here are the links to some great websites and some specific topics:

http://www.nature.com/scitable/topic/chromosomes-and-cytogenetics-7 (Chromosomes and cytogenetics) - scroll to the bottom to Explore this Subject - LOTS of topics to choose from!!!

http://www.genome.gov/

http://rarechromo.org

http://trisomy16.org

http://c22c.org (cat eye syndrome)

http://pkskids.net (Pallister-Killian syndrome/tetrasomy 12p syndrome)

http://chromosome18.org (Ring 18)

Explanation / Answer

X inactivation

The reason i chose X inactivation as my topic is because it is very intriguing. to come up with X inactivation in females to balance the products of the many genes present on the X chromosome in both male and female is a true testament to the complexicity and simplicity of molecular biology. The importance of the crucial process is realised when the unregulated process of X inactivation leads to various dieases and also tumor development

What is X-inactivation? Its a normal process that occurrs in females in their somatic cells. Sex determination in mammals is as follows: XX- female and XY in male. In female's somatic cells one of the X chromosome is randomly inactivated to balance out the gene products in both male and female. The inactivation is heterochromatization of the whole chromosome so that it does not trancribe its genes (transcription repression). The inactivation is random i.e. off of the two X chromosomes, any one might be inactivated. This leads to different phenotypes pertaining to the genes present on the X chromosomes. A very popular example is the coat color of the calico cat which has patches of two colors. Lets say in a cat there are two colors orange and white which means the coat color is controlled by the genes on X chromosome and each X chromosome carries different allele for color one being orange other being white. some cells express orange allele producing orange fur, other produce white fur because they express the white allele present on the other X chromomsome. The inactivated X chromosome can be seen under the microscope on the nuclear enevelope as a dark spot call Barr Body. The number of Barr bodies is one less than the number of total X chromosomes present, as in normal females there are two X chromosome hence the number of barr body is 1. If due to a condition there are three X chromosome then the number of Barr bodies will be 2.

Now, coming to the mechanism of X-inactivation. X-inactivation is an interplay between the expression of two different non-coding RNAs, XIST and TSIX. The X-chromosome that is to be inactivated produces this XIST RNA which then coats the same X chromosome and inactivates it. Simialry an antagonist RNA TSIX is produced from the RNA that remains active. FUnction and expression of both the RNA is opposite as there coding sequence.

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