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In mendelian experiment, yellow seeds were seen to be dominant over green seeds. The peas I've seen are generally green and not yellow. Did he use a different variety of pea plant ? The other trait that was seen was white or grey seed coat where grey is dominant over white. Why are these results not consistent with the peas found in pea pods ?

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  • $\begingroup$ If I had to guess, they were varieties of pea plants that we aren't accustomed to dealing with. $\endgroup$ – L.B. Jan 19 '17 at 13:11
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    $\begingroup$ The yellow colour of pea seeds is a rare trait and is found in many parts of the world ,China and Fiji islands for example. It's not usually found in Indian market though.(Wikipedia) $\endgroup$ – Tyto alba Jan 19 '17 at 14:02
  • $\begingroup$ @SanjuktaGhosh I think that's what OP is looking for, and you should submit it as an answer! $\endgroup$ – Gaurav Jan 19 '17 at 21:04
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    $\begingroup$ @Gaurav Probably Remi got it right, OP has confounded the concept of dominance with one of high frequency. $\endgroup$ – Tyto alba Jan 19 '17 at 21:11
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You are confounding the concept of dominance with the one of high frequency. The dominant phenotype might be at lower frequency than the recessive phenotype.

Dominance

Dominance in genetics is a relationship between alleles of one gene, in which the effect on phenotype of one allele masks the contribution of a second allele at the same locus

Trait frequency

Let's imagine a case where A is dominance and a recessive. Let, $f$ be the frequency of A alleles in the population. The frequency of individuals that have the dominant phenotype is the frequency of AA individuals plus the frequency of Aa individuals. Under Hard-Weinberg assumptions, the frequency of individuals having the dominant phenotype is therefore

$$f^2 + 2 f (1-f)$$

The frequency of individuals having the recessive phenotype is $(1-f)^2$.

If

$$f^2 + 2 f (1-f) < (1-f)^2$$

reorganizing the in-equation yield to

$$f < 1 - \frac{1}{\sqrt{2}}$$

So under the condition that $f < 1 - \frac{1}{\sqrt{2}}$, the dominant phenotype is present at lower frequency than the recessive phenotype.

If the calculations were unclear to you, then you should have a look at the wikipedia article of Hardy-Weinberg principle.

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  • $\begingroup$ @AnamikaGhosh As you have not reacted yet, I suppose I may fail to answer your question. If there is anything unclear, feel free to comment on it. $\endgroup$ – Remi.b Jan 23 '17 at 1:25

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