• Categories

  • Most Popular Questions

  • Recently Viewed Questions

  • Recent Answers

    How To Make a Digita… on What does a frequency of 100 H…
    Daigrepont on Can an earthquake cause air tu…
    Benedict on How did God come into exi…
    joshua on How does the human body g…
    Ian on How did God come into exi…
  • Recent Questions

  • Blog Stats

    • 2,227,323 hits
  • Visitors since 11-3-08

    counter create hit
  • Terms and Conditions

  • Warning

    We are doing maintenance on this site, so some posts may disappear for a short time. Sorry. Normal service will soon be resumed...
  • Pages

  • March 2008
    M T W T F S S
    « Feb   Apr »
  • Archives

  • Meta

  • Advertisements

What makes a gene recessive or dominant?

What makes a gene recessive or dominant?
Hettie Miller from Devon (Aged 15-25)


2 Responses

  1. Dear Hettie,

    I think you mean recessive allele rather that recessive gene. Each gene in humans is present in two copies. One copy comes from your mother and one copy comes from your father. Each copy of the gene may come in a different form or allele. The gene encodes a function usually via a protein but some times via a RNA molecule. Proteins and RNAs often have enzyme functions. They also often have regulatory functions, for instance, the may switch on or switch off a group of genes. One form or allele of the gene might be non-functional, i.e. the encoded enzyme does not work. Therefore you may have a non-functional allele and a functional allele. In which case the presence of a functional allele compensates for the non-functional allele, i.e., the functional allele is “dominant” to the “recessive” non-functional allele.

    A good example is eye colour in humans. The allele for brown eye colour encodes an enzyme, tyrosinase that produces melanin, a brown pigment. The allele for blue eyes encodes a non-functional tyrosinase. Thus if you have two blue eye alleles you will have no tyrosinase and hence blue eyes. If you have two brown eye alleles you will have two doses of tyrosinase and so will have brown eyes. If you have one blue eye allele and one brown eye allele you will have one dose of tyrosinase which is enough to give you brown eyes. i.e., brown eyes is dominant to blue eyes.

    In some cases e.g. flower colour, you can tell the difference if there is one dose of the gene product or two doses. If you cross a red flower (two red flower colour alleles) with a white flower (two white colour alleles) the off spring are pink (one red colour allele and one white colour allele). In this case the red colour allele that encodes a pigment production enzyme is “semi-dominant” over the white colour allele that does not encode and enzyme

  2. Whether a gene is recessive or dominant depends on the effect of the gene product, the protein, on the cell. So lets take two diseases as examples.

    Cystic fibrosis is recessive disease, you need to have both copies of the gene effected to carry the mutation in order to get the disease. This is as the CFTR (or cystic fibrosis transmembrane conductance regulator) protein when it is mutated has no effect on the cell other than it doesn’t do its job. So as you have one copy of the gene that is fine and so set of proteins from that gene that is fine, then you do not get the disease. Only when you have two copies of the gene that are mutated then you have no functional protein then you get the disease. Hence cystic fibrosis is a recessive disease.

    Huntington’s disease is dominant. This is because the mutated gene product, the protein, has negative effects on the cell other than not doing what it is supposed to the doing. So you can get the disease with only one copy of the mutated gene which causes disease.

    This is quite a simple way of looking at it, as the concept of dominant and recessive is difficult to see when you are looking at what a protein does on a cellular level, especially when it is involved with lots of other proteins

    Melissa Wragg

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: