According to Mendel's laws traits do not show any blending. So according to his laws people only with fair or dark skin should exist. Do the alleles in this case blend? And why?


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    $\begingroup$ There are several traits that do not follow the simplistic Mendelian rules. With skin colour, the trait is actually polygenic (and also quantitative). $\endgroup$ – WYSIWYG Jun 21 '16 at 18:09
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    $\begingroup$ Mendel also fudged his data. Traits blend all the time. $\endgroup$ – MattDMo Jun 21 '16 at 23:32
  • $\begingroup$ this question has been well addressed here: biology.stackexchange.com/questions/34565/… ( so I guess it might be marked as duplicate ). $\endgroup$ – Fabrice NEYRET Dec 21 '16 at 9:10

Mendel's laws were very basic to aid in the comprehension of genetics. You think of Mendel's genes as an +- pair where + is dominant and - is recessive, making our +- gene produce offspring with the + trait but still being a carrier of the - trait.

However, when it comes skin colour, eye colour, hair colour, height, tendency to muscle growth, and a thousand other things, the gene is more like a series of ++-++-+++-, + is more recessive than -, but some of + will still show up over -.

In short, the colour of a person's skin is not a simple +- gene of dark and fair; everyone carries a certain amount of pigment genes and certain number of non-pigment genes. The amount that one carries of each of the genes will determine his skin colour and his/her ability to pass on the dark/light characteristic.

  • $\begingroup$ To give a basic idea about the dimensions: if I remember correctly, from genome-wide association studies, height is currently known to be influenced by approx. 500 genes - that is 2-3% of all approx. 20000 protein-coding genes. However, studying these loci explain only about 20% of the variation seen in the phenotype height. $\endgroup$ – AlexDeLarge Jun 21 '16 at 17:56
  • $\begingroup$ A minor suggestion: Instead of X and Y use some other symbols. X and Y can be confused for chromosomes. $\endgroup$ – WYSIWYG Jun 21 '16 at 18:10
  • $\begingroup$ Good point, @WYSIWYG . Hadn't thought of that. $\endgroup$ – anonymous2 Jun 21 '16 at 19:29

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