Re: Incomplete dominance
Date: Tue Dec 8 17:51:29 1998
Posted By: Carl Mayers, Grad student, Plant Sciences, Cambridge University
Area of science: Genetics
ID: 910572858.Ge
Message:
Ok, let's take this step by step.
Firstly, let's say the the colour of the flower is controlled by this
incomplete dominance gene. The gene comes in two alleles (different
forms), and the flower will always have two copies of the gene (as it has
two chromosomes, each containing the gene). Let's call these either R
(red) or W (white)
- A plant which has red flowers will have two copies of the red gene, so
its' genotype (the genes it contains) will be RR
- A plant which has white flowers will have two copies of the white gene, so
its' genotype will be WW.
- And we cross these two:
- Parent 1 (red) genes = RR
- Parent 2 (white) genes = WW
- Offspring = RW (one gene from each parent)
As the flower colour is controlled by incomplete dominance the offspring
will all be pink (half way between red and white). We now take this pink
flower (RW) and cross it with a white flower (WW). The offspring
get one of their genes from parent 1 (white), so one will always be a white
gene. The other gene will come from the other parent (pink, RW), and it
has a 50/50 chance of being either a white or a red gene.
This means the genotypes of the offspring here will be either WW or
WR. This means that half the new plants will have white flowers
(WW) and half will have pink flowers (RW).
It was this sort of experiment which originally led to the discovery of
genes being seperate, indivisible things. You can't make a pink flower
whiter or redder by crossing it with a white or red flower. You can only
get white, red or pink, and never any more blending than this.
Here's a good site to look at for more information:
Gene interactions
Hope this helps!
All the best, Carl
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