Essay - Free essays!
Login to an existing account
GCSE essays
A Level essays
University essays
Why join?
Essay quality

Search forums
About us
Contact us


Polygenes and environmental factors Free essay! Download now

Home > A Level > Biology > Polygenes and environmental factors

Polygenes and environmental factors

You can download this essay for free. All you need to do is register and submit at least one of your essays to us.

Or you can purchase this essay for just $2 instantly without registering

Downloads to date: N/A | Words: 1256 | Submitted: 12-May-2011
Spelling accuracy: 95.7% | Number of pages: 9 | Filetype: Word .doc

This is what the first 3 pages of the essay look like

Polygenes and environmental factors essay previewPolygenes and environmental factors essay previewPolygenes and environmental factors essay preview


What are polygenes?


Interaction of genes – polygenes and environmental effects
Polygenes are a group of genes that get together to control one characteristic. Characteristics that are controlled by polygenes are the following:
Human height
This is the best example for that can be explained under polygenes because this is controlled by 6 genes such that if you possess more than three genes for tallness you are bound to belong beyond the average height and vice versa which can be easily shown by the following graph.

Yet this characteristic is also affected by environmental factors which include the diet most importantly, that is even if you posses genes for extreme tallness, if you do not properly intake a diet rich in Ca still you won’t reach up to that height and similarly if you consume a lot of Ca in your diet then even if you have genes for dwarfness you still reach up to a tall level.

Skin colour in humans
This is another characteristic controlled by polygenes. These genes influence the production of melanin by cells known as melanocytes. Melanin is a pigment responsible for the skin colour and there are two types:
Black-brown pigments
Red-yellow pigments
This production is controlled by 3 or 4 or more genes and thus more the amount of brown-black melanin pigments you posses, darker your skin colour is and likewise more the number of red-yellow pigments you posses, more the fairer you are.
Exposure to UV light will increase the production of melanin thus, UV light act as stimulants for melanocytes which results in getting a skin tan. Thus, this shows that skin colour in humans are also under the influence of the environment.

Animal hair colour
Hair develops under the germinal layer. Its colour is under the influence of melanin which creeps into the hair strands too. In animals, coat colour differs in winter and summer seasons, that is in the winter season the coat colour is white (since white is neither an absorber nor an emitter of heat) while in the summer season its black (black is both a good absorber and an emitter). This happens by a process known as moulting (falling off of hair once a year and regrowth under environmental effects).
Tyrosine is a protein which is responsible for the production of melanin by the convertion of an enzyme called tyrosinase. Mutations in this enzyme occur and when it does tyrosinase found in the skin is no longer converted into melanin. This causes a condition known as albinism where the skin colour is white due to the absence of melanin in the skin. These enzymes are also found in the skin of animals, mostly in cats where it shows up as black/brown etc… and white where black patches denote as the ...

Download this essay in full now!

Just upload at one of your essays to our database and instantly download your selection! Registration takes seconds

Or you can download this essay for $2 immediately without registering

Comments and reviews

Reviews are written by members who have downloaded the essay

No comments yet. If you download the essay you can review it afterwards.