Yes, the reason Down Syndrome increases exponentially with increasing maternal age is because of the decreasing quality of the eggs. What happens is this: As the eggs age, their ability to properly undergo meiosis (cell division of gametic cells) is greatly impaired. Women are born with all of their eggs, yes, but these eggs are not actually mature in the typical sense. They are formed in the womb, but the eggs are "frozen," in a sense, until it is time for them to be released from the ovarian follicle. So, they do not completely undergo meiosis and they are stuck in a stage in the meiotic cycle.
When it's time for the egg to actually divide, the chromosomes must split. In meiosis, there are actually two sets of divisions. Sperm and eggs are, essentially, undergoing mitosis (somatic cell division) twice. This is to reduce the number of chromosomes into half- go from 46 to 23. It is an ingenious biological solution to stop the number of chromosomes from multiplying exponentially each time a zygote is created. (This is also how gender is determined- the sperm only have one of the sex chromosomes, either an "X" or a "Y," rather than both, like what is seen in their body cells. So, the sperm carrying a lone "X" chromosome in its 23 will create a female; the "Y" sperm will create a male.)
Anyway, with the older eggs, their ability to properly distribute the proper number of chromosomes is greatly disturbed. Sometimes, as the chromosomes are pulling apart, they simply don't pull apart. Thus, there are either too few or too many chromsomes in a cell. In the case of Down Syndrome, there are three copies of Chromosome 21, which is why Down Syndrome's "technical" name is "Trisomy 21." The three copies come from the fact that the mother's egg (usually- although, it could be a meiotic mishap from the father's sperm) didn't split apart its two copies of Chromosome 21, so the egg still had two copies, rather than one. Once the sperm fertilized the egg, the sperm's copy of Chromosome 21 brings the total to three copies. Normally, there would only be two copies- one from each parent.
And they are finding that autism may be linked to increasing
paternal age. It seems ASD's are just more likely to be involved with the father. Simon Baron-Cohen's term of autism being an "extreme male brain" probably has something to do with it. And it usually is true. Most of the girl Aspies I know (myself included) aren't interested in typical "girl" things, like make-up, hair, clothes, and shopping. It may help explain why there is a 4:1 boy:girl ratio in ASD's.
-GatsbyLuvr1920-
Linear Mode
