Human phenotypic characters & Genetic Plays

[LJP07]

Epistasis occurs in the following example of shapes of fruit. This is actually a common example and if you do study Genetics in more detail, I'm sure this example would come along.

 

Remember Epistasis is the expression of one gene dominantly over a separate gene on different loci.

 

The fruit colour of say a Mango has three colours Pink, Purple and White just for arguments sake. These have the letters Pi, Pu, and W. When two genes are needed for the Pheontype, we refer to this asComplementary Gene Action.

 

If you have a Purple Allele that cancels or inhibits all the Pink ( P,p ) from being expressed, the (P,P) is referred to as having Dominant Epistasis.

 

Another example of Epistasis is referred to as Dominant Suppression Epistasis, the term suppression refers to a factor that inhibits the functions of alleles at a completely different Locus. This happens when one of the Epistatic genes prevents the function of a Locus at a certain place governed by certain genes.

 

Seen as were referring to genes a lot, another term you may come across is Pleiotropic. This refers to any gene that affect not one, but many Phenotype. Another term you may commonly come across to is Haploinsufficiency this refers to when a protein produced by a gene is not above it's activation to become functional to the body. An organism is said to have a Monosomy where is contains only one copy of chromosomes.

Finally the last term you may come across is Allotetraploidy this refers to having diploid copies of chromosomes originating from a alternate parental species.

 

Hopefully this helps to improve you knowledge of Epistasis and related jargon.

[Pyrotex]

isnt these statements controversial?

or is it meant that the protiens produced could replace an already existing phenotypic character?

or is it meant that the altered gene sequence in the embryo of drosophila could make the alterations?....

Difficult to answer as your questions are not clear.

First, my statement that (in general) genes code for proteins is NOT controversail. It is accepted by all geneticists. Remember, each codon (group of 3 consecutive letters of the DNA code) codes for a single amino acid. Sequences of codons code for a sequence of amino acids. A protein is defined as a sequence of linearly connected amino acids.

 

Proteins do have chemical properties, but by and large, their geometric and kinematic properties dominate. In other words, it is the shape of the folded protein molecule, and its ability to flex or rotate at certain points in the molecular chain that give the protein molecule its power to cause biochemical reactions within the cell.

 

If you replace a protein with a very similar (but different) protein, it is likely that you have changed the shape and kinematics. Different biochemical pathways will be disabled or enabled.

 

How THIS alters the phenotypic attributes of the total organism, is not clear, not well understood, not mapped out, except for a handful (a few hundred) of rare exceptions. For example, eye color, cycle cell anemia, and a number of genetic disorders.

[Pyrotex]

The fly leg example is not that clear cut either. In developmental biology the location and layout of the body is determined by many, many genes all interacting in gradients. That is how (for the most part) you always have the head up and the tail down and (in our case) two arms where they are supposed to be.

It is reasonably clear cut. Of course you must realize that drosiphilia is a much simpler organism than a mammal. Having a single gene mutation cause a human to have three arms and one leg is very unlikely. Although having a single gene mutation produce two-headed calves happens often enough.

 

But it's a fact that one can induce a leg to grow where an antennae should be in a fruit fly by changing (mutating) one gene.

[sreerag16]

its very nice of all you people..

thanks for the detailed discussions..

will point to my doubts later..