[SunkenCiv]

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YOU

This diagram works for most people, but not for folks with Down's Syndrome and a few other conditions. F is for father, M for mother; each of us has up to 64 great-great-great-great-grandcestors; no more than 46 of them has had even one chromosome pair reach you; even with the occasional crossing stream (I don't have even one such pair in my known ancestors, but some of my cousins do) there's no more than 46, and with crossing streams, could be less.

[Joya]

And for this, thanks, plain text much clearer, and
Qx. ping.

[Quix]

Have you participated in the Nat Geo DNA study?

I’ve been somewhat disappointed in the results—always more money for not that much more info, imho.

Still it’s interesting.

[gleeaikin]

Regarding chromosomes and persistance of traits. My late husband and I visited ancestral property in southern Illinois a few years before he died in 2005. We found a distant relative on adjacent land. It turned out they had a common ancestor in the late 1700’s. There were certain physical similarities, around the eyes, and they both had similar long fleshy ears. In my husband’s case it was the great grandfather. For the other man it was the great, great grandfather. His line married at a younger age.

Regarding fitness, I think it is survival of the more fit, but as conditions often change, what fit is also tends to change. Vive la diferance.

[mad_as_he$$]

Humm. I questioned you assertion there so I went and looked at both Mrs. Mad’s family tree and mine. She has much more center in Scotland and Ireland where my tree is allover Scandinavia, Germany and England. In both our trees you supposition seems to be true. Interesting.

[allmendream]

Why wouldn't this work for Down’s syndrome? They have just as many great^nth power grandparents as anyone else on average - they just got an extra copy of chromosome 21 during cell division of their initial gametes.

And you don't get chromosomes unchanged from a grandparent or great grandparent. The chromosomes you inherited from mom are almost exactly a 50/50 inheritance split between her mom and dad - and the chromosomes you inherited from dad are almost exactly a 50/50 inheritance split between his mom and dad.

Recombination frequency is measure in “centimorgans” which correspond to a % chance that a crossover event will happen between two chromosomal markers (mixing and matching mom and dad's DNA along the chromosome to make reproductive cells). It is about a 1% chance to have a cross over every 15,000 nucleotides.

The human genome is on 46 chromosomes and consists of 3 billion base pairs. That makes the scale of 15,000 nucleotides pretty small.