pedigree relation?

Question

if the dad in the family is Aa and the mom is aa
they had a son in this family is aneuploid(trisomy 18)
in which parent did the error in meiosis occur?
at what stage of meiosis did it occur?

from the info, can i determine if the error occur in anaphase I or II

Answer 1

The mom, because it's a recessive autosomal disease

Errors in chormosone numbers most often occur in Anaphase I and Anaphace II of meiosis
(Remember meiosis has two stages)

In both anaphases, the chromsones in normal circumstances separate and move to opposite poles in even numbers.
When non disjunction occurs, the chromosones do not divide equally and one cell will end up having more chromosones then the other.

Answer 2

The coefficient of relationship (RC) provides a way of objectively assessing the similarity of two pedigrees by giving a number that is a direct measure of shared ancestry. In most human populations, two individuals picked at random would likely have a RC of 0, a brother and sister 50% and identical twins 100%. Other relationships would fall between 0 and 50%.
The number generated may be viewed as analogous to the % composition, except that you are comparing two dogs instead of looking at one. A brother and sister will give a value of 50% as long as an ancestor is not repeated. Once ancestors start to repeat, the individuals no longer have an inbreeding coefficient of zero. Two sibs from a highly inbred line may have an RC of 80% or more, and two dogs that are not sibs may have an RC above 50%.

The formula for the RC is:
RAB = 2fAB ÷ [(1 + FA)(1 + FB)]½
where fAB is the inbreeding coefficient of a hypothetical litter between A and B, and FA and FB are the inbreeding coefficients for the two individuals, A and B.

A simpler approach to the breeder's problem would be to compute the RCs for C vs D and E, and D vs E. This is not a pencil and paper calculation. However, presented with just such a problem, it took me about 2 minutes to obtain the three RCs with the latest version of CompuPed. My results were RCD 10.4%, RCE 13.4%, RDE 17.2%.

As D and E share the most common ancestry, so would the progeny from their two prospective litters, while C and D share the least. To minimize inbreeding and maximize diversity, they would be my choice, all else being equal. (These values actually all fall below the average for the breed, which is ~ 23%.)

much more on this