My understanding is that trisomy resulting from an abnormal of chromosomes present in either the sperm or egg does not result in a baby that can be carried to term, let alone survive infancy, 99.99% of the time. There's only ~3 chromosomes where their trisomy is long-lasting enough to have a name. Plus, if the egg somehow contributes 2 copies of a chromosome, it's not like the sperm just abandons the copy it brought to the table. Also, it seems that the main estrogen receptor is located on chromosome 6, the trisomy of which won't carry to term.
I'm not sure where you get the 100% similarity thing from.
Well, I was of the same opinion too - it simply did not follow textbook mitosis and the gamete formation. What I did not realize is that egg formation is a much more involved process having a series of cell division and chromosomal shedding via orbital body formation.
What I did not realize was that there were two different processes being described. One was the by-the-book process of creating these cells then the ideal combination of two gametes each with 23 chromosomes into a zygote with 46 that could then from a genetic standpoint be a 50% mix of the parents that could then go to term.
The second situation was where the egg's formation is not perfectly by the book and the sequence of division and shedding of chromosomal material is either not complete or fertilization happens but the formation of the orbital body does not occur properly.
Put basically the egg "selects" to complete and match up its 23 chromosomes upon the "trigger" event of fertilization however at that moment it is possible that previous orbital bodies or the formation of the orbital "house cleaning" body after fertilization can exclude contributions from the sperm.
The reason for my continued confusion was that the texts were not stipulating the possible ways that a zygote ends up with the normal 46 chromosomes.
Yes, if you do not end up with 46 you are going to have major problems.
For example I did not know about the post-fertilization formation of an orbital body that is then dumped from the zygote. This orbital body can contain a range of genetic material that then disintegrates. Orbital bodies are used in making a 46 chromosome egg cell into a 23 chromosome gamete egg. It is totally possible for the post-fertilization orbital body to capture nearly all or nearly none of the male's chromosomes and dumping them from the zygote.
This is all before the first zygote cell division and is in the period between fertilization and cell division when all this house cleaning is happening. It is this house cleaning that gets most zygotes back to 46 chromosomes either by adding or subtracting chromosomal material from the soup that is present post-fertilization.
Yes, typically the ratios are closer to 50% from each parent but the thing that was a total shock was that an egg could be released with still 46 chromosomes and could get fertilized by a malformed sperm and for a brief moment could have in excess of 69 chromosomes. Yet, it is possible for such a union to still end up with a 46 chromosome zygote if the house cleaning mechanisms function. The ratio in this situation would be about 2/3 mom and 1/3 dad or 33% dad.
To clarify (because it confused me too) we are not talking about an individual that has more than 46 chromosomes but rather the egg's ability to include or exclude a range of genetic contribution from the father because there may be extra maternal strands already in the egg or the egg may dump more of the male's in the subsequent orbital body formation.
Thus you can get an offspring that is genetically more like the mother and never more than about 50% of the father.
Bottom line is that things are never exactly like the book.