hardy weinberg

[medman88]

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Does anyone know how to apply what's on page 88 of FA 2012

"the frequency of an X - linked recessive disease in males = q, in females = q^2"

If anyone has one, an example would be great.

thanks

 

[withrye]

Colorblindness is carried on the X chromosome and is recessive. There are two allele frequencies, p (let's say for functioning pigment) and q (for colorblindness). Males have only one X chromosome, so they carry those allele frequencies at those same rates, p and q. This means that the frequency of colorblindness in males is q, while the frequency of normal sightedness is p.

For females, things work as they normally do in Hardy-Weinberg. With two X chromosomes, there are two alleles to consider, so there are four possible combinations: pp, pq, qp, and qq. This is why they say the genotype frequencies are p^2, 2pq, and q^2. Because colorblindness is recessive, a female needs two q alleles to be colorblind, which occurs at the rate of q^2. Remember that for males, any appearance of q is sufficient since there is no other X chromosome to compensate.

Please let me know if you need clarification, or if this wasn't what you were asking.

 

[Phloston]

Random tidbit:

Deuteranomaly is the most common type of color blindness (less sensitive, rather than deficient, green cones). In terms of genetics, any recessive trait that is expressed with > 5% frequency in the population must confer a biological advantage. Because deuteranomaly occurs in 5-8% of the male population, it must be advantageous.

--> Apparently it's been found in military studies that some men can see camouflage that others can't see. Perhaps it's therefore a hunter-gatherer benefit.

--> Also, any mother of a prota-, deuter- or tritanomalous male is tetrachromatic. This is why some studies say women can "see" colors better than men.

 

[withrye]

Random tidbit:

Deuteranomaly is the most common type of color blindness (less sensitive, rather than deficient, green cones). In terms of genetics, any recessive trait that is expressed with > 5% frequency in the population must confer a biological advantage. Because deuteranomaly occurs in 5-8% of the male population, it must be advantageous.

--> Apparently it's been found in military studies that some men can see camouflage that others can't see. Perhaps it's therefore a hunter-gatherer benefit.

--> Also, any mother of a prota-, deuter- or tritanomalous male is tetrachromatic. This is why some studies say women can "see" colors better than men.

I don't want to derail this topic, but could you provide some citations for all of those facts? Namely the >5% criterion, camouflage effect, and back heredity of tetrachromaticity. I've never heard of any of that before, but it all falls under damn interesting and I'd like to learn more.

 

[alternatego]

I cannot help but feel profoundly mentally ******ed each time I try to really understand genetics

 

[Phloston]

I don't want to derail this topic, but could you provide some citations for all of those facts? Namely the >5% criterion, camouflage effect, and back heredity of tetrachromaticity. I've never heard of any of that before, but it all falls under damn interesting and I'd like to learn more.

I had actually done a practice question at some point that asked for which level of validity, on the USPTF evidence-based medicine scale, information on forums ranks. The answer was III. Opinions of respected colleagues/forums --> III; II-2 --> cohort/case-control studies; II-1 --> controlled trials without randomization; I --> RCT.

(I have that annotated into my FA)

The only reason I say that is because I don't remember offhand where I had seen/picked up that genetics info. I had definitely read it somewhere though. Therefore, that information is not concrete, but rather a III on the USPTF validity scale.

 

[medman88]

Colorblindness is carried on the X chromosome and is recessive. There are two allele frequencies, p (let's say for functioning pigment) and q (for colorblindness). Males have only one X chromosome, so they carry those allele frequencies at those same rates, p and q. This means that the frequency of colorblindness in males is q, while the frequency of normal sightedness is p.

For females, things work as they normally do in Hardy-Weinberg. With two X chromosomes, there are two alleles to consider, so there are four possible combinations: pp, pq, qp, and qq. This is why they say the genotype frequencies are p^2, 2pq, and q^2. Because colorblindness is recessive, a female needs two q alleles to be colorblind, which occurs at the rate of q^2. Remember that for males, any appearance of q is sufficient since there is no other X chromosome to compensate.

Please let me know if you need clarification, or if this wasn't what you were asking.

this was great, thanks!