Genotype-phenotype correlation & variable expressivity

[Mendel]

Hi

 

What is the difference between genotype-phenotype correlation & variable expressivity in genetics?

What is the definition of each?
What is the difference between them?
What is the relationship they have with each other?

These questions are confusing for me,

Please help me find the answers to these questions.

Edited April 10, 2013 by Mendel

[pwagen]

With the risk of this being homework, here are the definitions I could find. Try and work the other questions out from them, and ask more questions if you run into problems.

 

 

The association between the presence of a certain mutation or mutations (genotype) and the resulting physical trait, abnormality, or pattern of abnormalities (phenotype). With respect to genetic testing, the frequency with which a certain phenotype is observed in the presence of a specific genotype determines the positive predictive value of the test.

 

Genotype-phenotype correlation

 

 

Variable expressivity occurs when a phenotype is expressed to a different degree among individuals with the same genotype. For example, individuals with the same allele for a gene involved in a quantitative trait like body height might have large variance (some are taller than others), making prediction of the phenotype from a particular genotype alone difficult. The expression of a phenotype may be modified by the effects of aging, other genetic loci, or environmental factors. Another example is neurofibromatosis, where patients with the same genetic mutation show different signs and symptoms of the disease.

 

Variable Expressivity

[Mendel]

Thank you dear pwagen,

What can be the cause of the variable expressivity?

I read somewhere that due to different mutations in a gene or mutations at different positions of a gene,In your opinion, is this true?

This definition is similar to the definition of Genotype-phenotype correlation!!!!

[pwagen]

Before this gets out of hand, I want you to know I'm not a biologist. So not only am I just finding this out as I'm reading up on it, I might be very very wrong. So take whatever I say for what it is!

 

What can be the cause of the variable expressivity?

The Wikipedia article mentions a few causes, for example aging or environmental factors. Also, a trait might be due to more genes than what is currently known, which means that the genes known to effect a certain trait might not be enough to explain the differences. I don't know if that would be an example of variable expressivity, but that's how I understand the Wikipedia article and the links from it.

 

As an example, take two identical twins. One grows up normally, the other one has an accident when he is a kid, involving a bunch of chemicals which makes him blind. But it also gives him the ability to "see" sound. The other twin is exposed to a radioactive experiment when he is an adult, which turns him green and muscular when he is upset. Both have the same genes, but they would have different traits.

I read somewhere that due to different mutations in a gene or mutations at different positions of a gene,In your opinion, is this true?

In my uneducated opinion, I would say no. The whole point of variable expressivity seems to be that the same genes can produce different traits. If the genes are different, that would be an example of genotype-phenotype correlation (the genes change, so the traits change), but not any kind of variable expression?

This definition is similar to the definition of Genotype-phenotype correlation!!!!

And you seem to agree! Hopefully I'm not as wrong as I feel I might be.