Genotype and allele frequency

[Sir Gillies]

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Hi everyone,

I have come across these two frequencies on Kaplan LN but I still don't understand how to calculate them.
Kaplan uses RFLP as an example stating that there are two possible alleles, labeled 1 and 2, there are three possible genotypes: 1-1, 1-2, and 2-2. I then provides counts etc all on page 333.

Could someone clarify how to calculate the frees frequencies and what does 1-1, 1-2 etc stand for?

Thanks in advance a lot for your help.

 

[chaotic mind]

I will try to explain it with an example,sickle cell anemia
the gene is the beta globin gene.
and there is a possibility of inheriting two alleles-either the normal allele 1 or mutant allele 2.since there are only two alleles then frequency of allele 1 + 2= 1(100 percent).that takes care of "allele frequency"

every person inherits two copies of the beta globin gene,this determines their genotype.
possible genotypes are
1-1 homozygous normal
OR 1-2 carrier
OR 2-2 homozygous,diseased .
the relationship between the genotype frequencies is given by the hardy weinberg equation
where allele 1=p and 2=q

 

[chaotic mind]

I will try to explain it with an example,sickle cell anemia
the gene is the beta globin gene.
and there is a possibility of inheriting two alleles-either the normal allele 1 or mutant allele 2.since there are only two alleles then frequency of allele 1 + 2= 1(100 percent).that takes care of "allele frequency"

every person inherits two copies of the beta globin gene,this determines their genotype.
possible genotypes are
1-1 homozygous normal
OR 1-2 carrier
OR 2-2 homozygous,diseased .
the relationship between the genotype frequencies is given by the hardy weinberg equation
where allele 1=p and 2=q

i wanted to point out that phenylketonuria would be a better example than sickle cell anemia.since there can be three alleles for sickle cell...normal,sickle cell and hbC and not two.

 

[withrye]

To wrap up what chaotic mind said, you have two alleles (let's say p and q) for one gene. Each person has two copies of the gene, so they can either have two p alleles (pp), two q alleles (qq) or one of each (qp or pq, equivalent). This is what Hardy Weinberg equations mean when they say the homozygous genotype frequency is p^2 or q^2. You take the probability of having a p allele or a q allele and multiply it by the probability of having the identical allele.

The heterozygous case is the probability of the qp case plus the probability of the pq case. Since they are equivalent, this is just 2pq.

 

[Sir Gillies]

Thanks a lot guys for all the replies. I really dislike biochem!!! Just finished the Kaplan LN that took me more than expected : (