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

My question then is, what is the chance a given allele 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 an allele 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 alleles, each on one of two pairs of chromatid attached to each other. There is 50% chance for a given allele to cross over. For example, the chance for both desired alleles 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 alleles 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 allele) will be assigned to the desired daughter cell. However, in the case where a desired allele is found in both homologs (2/4 of a chance), then the chance that at least one desired allele 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 allele will be assigned to a given cell (in this case the gamete). However, if the desired daughter cell contains two of the desired alleles, then there is a 100% chance that the cell will have the desired allele.

In conclusion, the chance I estimated that the gamete will have at least one desired allele 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
  • $\begingroup$ Gametes do not undergo meiosis (at least under normal circumstances). Since you seem to be having ongoing trouble with basic concepts and terminology in genetics I strongly encourage you to take advantage of the many online resources available for making sure you have the background required for understanding this field. Suggestions to follow ... $\endgroup$ – tyersome Jun 19 at 18:25
  • $\begingroup$ I have found that when learning about a new area starting with a relatively accessible and reliable source like Khan Academy is very helpful. Wikipedia is also generally a good starting point and you can then check their references. Online platforms called MOOCs offer free (or very low cost) courses on a wide variety of subjects — two I am familiar with are Coursera and edX. Finally, textbooks with a good level of detail are also freely available online e.g. from NCBI. $\endgroup$ – tyersome Jun 19 at 18:26
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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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