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Let us say a somatic cell had a desired gene. This somatic cell was replicated during interphase so that it had two of the desired gene. It then underwent meiosis.

My question then is, what is the chance a given gene will end up in a given gamete that will be involved in conception?

Firstly, there is a 50% chance a chromosome will be assigned to a given daughter cell. This is because of independent assortment. In addition, cross over occurs at chiasmata. Lets assume then that there was a 50% chance that a gene will be crossed over (although this probability may be far from true)

The process during meiosis is that cross-over occurs first. We have two desired genes, each on one of two pairs of chromatid attached to each other. There is 50% chance for a given gene to cross over. For example, the chance for both desired genes to cross over is 1/4 (1/2 x 1/2), the chance only one will cross over is 2/4 (since either of the two desired genes can cross over).

Then there is the first independent assortment during meiosis I which produces the desired daughter cell. In this case there is a 50% chance that a given chromatid pair (containing the desired gene) will be assigned to the desired daughter cell. However, in the case where a desired gene is found in both homologs (2/4 of a chance), then the chance that at least one desired gene will be in the daughter cell is 100%.

Finally, during meiosis II, another independent assortment occurs which produces the desired gamete. The same rule applies with a 50% chance a given gene will be assigned to a given cell (in this case the gamete). However, if the desired daughter cell contains two of the desired genes, then there is a 100% chance that the gamete will have the desired gene.

In conclusion, the chance I estimated that the gamete will have at least one desired gene is 50%. Although, I'm not sure if this is correct. Anyone mind confirming this.

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  • $\begingroup$ "Let us say a somatic cell... then underwent meiosis" Somatic cells don't undergo meiosis. $\endgroup$ – De Novo Aug 13 '18 at 20:30
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A cell contains two haplotypes (or two set of all chromosomes). One haplotype inherited from the mother, one from the father. A haploid cell, resulting from meiosis, will receive either the maternal (or grandmother if you prefer) or paternal (or grandfather if you prefer) haplotype. It cannot receive anything else. Hence the probably must be 0.5 (or 50%).

Note that you are using the term "gene" incorrectly. You should use the term "allele" instead. And while you are improving your genetic vocabulary you should also check the term "locus". Also, the term "desired gene" is never used. We talk about "beneficial allele" or "detrimental allele".

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    $\begingroup$ I think "desired gene" is to mean "allele of interest" for purpose of calculations. $\endgroup$ – Cell Aug 13 '18 at 22:36
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You are making this too complicated. There is a 50% of any particular allele ending up in a gamete. The end.

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