Posts by ironraven11

These frequencies are calculated at the population level—basically, based on the specific country where the people being tested live. There are pre-calculated tables created by specialists for this exact purpose. You then plug those values into formulas derived from the various combinations of maternal, paternal, and fetal alleles. So, regarding your question about whether the formula for the second locus, D21S11, is identical... it doesn't necessarily have to be! It all depends on which specific allele combinations you're looking at (there’s actually a table for that too)

As for genetic recombination—our term for it might be "crossing over"—that's when intertwined chromatids break and reconnect, allowing homologous chromosomes to swap genetic material. (This happens during meiosis I, specifically during prophase I)
The actual site where genetic recombination occurs is called a chiasma.

For anything else, you really ought to check with a specialist.🙂

Angela Bailey7 said:Since nobody seems to have replied yet, I'll just try rephrasing my question...

If we're looking at DNA testing for maternity and paternity—say the mother is AB and the father is CD—could they have four different offspring combinations by taking one allele from each parent? Like AC, AD, BD, and BC?

Also, does that mean the first allele listed at a locus will always be from the mom and the second from the dad?

For example:

Mother Father Child
AB CD AC
10,11 13,15 10,13

So, if the position at a locus like D8S1179 shows 13, 10, that would mean the 13 comes from the dad and the 10 from the mom—which doesn't fit those four possible combinations I mentioned... and I couldn't find any mention of a "CA" combination when searching online.

From what I remember, if you have this:

Child Mother Father
10,13 10,11 13,15
BA BC AC

In this case, the mandatory allele the child *must* inherit from the father is 13—and the formula just for that specific STR locus, D8S1179, is PI=1/2a (where 'a' is the frequency of that allele within the specific population you're testing).

Basically, you look at the mandatory allele—you don't just assume the first one belongs to the mom! For instance, if you assume the mom is AA and the child is AB, then that B allele absolutely has to come from the biological father. If the alleged father doesn't carry that B allele—meaning there's no way he could have passed it down—and you rule out a mutation at that specific marker, then you can exclude him...