linkage

[hj0517]

Hey guys - I'm having a little trouble understanding the concept of linkage with respect to genetic polymorphism and I was wondering if anyone could help me out?

I'm using HY CMB 99 and the clinical example it gives with APKD is a little confusing, I get the meiotic crossover bit - just don't understand the way linkage can be used to work out odds of getting X disease.

Thanks!

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[SomeDoc]

Hey guys - I'm having a little trouble understanding the concept of linkage with respect to genetic polymorphism and I was wondering if anyone could help me out?

I'm using HY CMB 99 and the clinical example it gives with APKD is a little confusing, I get the meiotic crossover bit - just don't understand the way linkage can be used to work out odds of getting X disease.

Thanks!

The odds of getting X disease (or more specifically, locus linkage) can be estimated based on the relative distance between two loci of interest. The closer the loci are on the same chromosome, the greater the chance of them being found together on a resultant gamete and vice versa, in the process of meiosis. Let's say that if a) both loci are needed to produce the diseased phenotype (assume autosomal dominant alleles for the loci, and an autosomal dominant mode of inheritance), b) and if the distance between these loci are small, you can conclude that there is a 1/2 chance (2/4 gametes) of producing a gamete with a diseased allele (which contains both loci).

 

[hj0517]

Thanks for that piece of information - good to know thats how I had it in my head, has anyone been asked to calculate odds for that or am I reading way too much into this bit of mol. bio for USMLE purposes?