How do we know the percentage of shared genes among relatives? - USMLE Forums
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#1
01-27-2011
 USMLE Forums Scout Steps History: Step 1 Only Posts: 65 Threads: 19 Thanked 53 Times in 25 Posts Reputation: 63
How do we know the percentage of shared genes among relatives?

hi everyone...

In this pedigree shown below I have read that
II 2, II 3, II 5 share 1/2 of their genes
and
III 1or2, III 3or4, III 5or6 share 1/8 of their genes

Want to know how disease gene sharing stuff among progeny is calculated???

#2
01-27-2011
 USMLE Forums Scout Steps History: 1+CK+CS Posts: 18 Threads: 2 Thanked 33 Times in 7 Posts Reputation: 43

These numbers are called coefficients of relationships. In order to calculate them you have to first understand that through meiosis and gametogenesis, each parent roughly transfers 1/2 of his genome to each of his progeny. Then using this principle you count the number of paths in the family tree connecting two relatives for whom you are trying to find the coefficient of relationship and then use it in this formula
Rxy = summation (1/2) to the power "n"

where Rxy is the coefficient of relationship between two relatives x and y. and "n" is the number of paths.

I might have missed a few points which could be critical for you to understand the concept, but you can visit the following link, for a better explanation:
http://www.genetic-genealogy.co.uk/Toc115570135.html

Keep in mind that, there would hardly be enough time for you to calculate coefficients of relationship in the exam so the common ones like siblings (1/2), half brothers (1/4), first cousins (1/8), half cousins (1/16) and second cousins (1/32) should be on your fingertips.
 The above post was thanked by: aktorque (01-28-2011), anoop_1198 (01-28-2011), im99 (02-18-2011), koolkiller88 (04-29-2012), korean (01-28-2011), Mondoshawan (01-27-2011), raheel_memon (01-28-2011), rozirose (01-28-2011), rsin21 (01-28-2011)
#3
01-28-2011
 USMLE Forums Newbie Steps History: 1+CK+CS Posts: 7 Threads: 2 Thanked 6 Times in 4 Posts Reputation: 16
great explanation

Thank you dr limple for this great explanation

#4
01-28-2011
 USMLE Forums Scout Steps History: 1+CK+CS Posts: 18 Threads: 2 Thanked 33 Times in 7 Posts Reputation: 43

You are very welcome

 Tags Genetics-

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