3 ms·

I think the point is that variation is created by taking some material from the mother, and some from the father. A _mutation_ also creates variation, but refer

I think the point is that variation is created by taking some material from the mother, and some from the father. A _mutation_ also creates variation, but refer to things like replications errors and "bit flips" due to, say, radiation.

13of40 8y ago
But those aren't differences in the same way that mutations are. The chromosomes passed on by the grandmother are identical to those received by the granddaughter, unless you're talking about spilicing genes between chromosomes. The morphological differences in the daughter are from the genes being expressed differently in the context of her body and the father's DNA. (Or so 90's science class would have me believe.)
- gonvaled 8y ago
  The daughter has some genes from the mother, and some from the father. Which genes are selected from which progenitor is random. To have a big pool for recombinations, inbreeding is to be avoided and populations must be big enough.
  - ratacat 8y ago
    My cryptological brain can't herp but replace here... The "selected at random" with "selected in ways we don't understand"
    - HeadsUpHigh 8y ago
      There are parts of the cell that are noise-based. I'm talking about quantum level noise so in many ways it's as random as it gets.
  - pygy_ 8y ago
    > Which genes are selected from which progenitor is random. IIRC that's not completely true. In mammal females, there is competition at the chromosome level to determine which member of each pair will end up in the first polar body (which is discarded) and which one ends up in the secondary oocyte (which then splits up to become the ovum and the secondary polar body).
- gus_massa 8y ago
  Each person has two chromosomes of each kind and they are mixed during the formation of the egg and sperms. For more details see https://en.wikipedia.org/wiki/Chromosomal_crossover https://en.wikipedia.org/wiki/Chromosomal_crossover So, ignoring mutations, the next generation gets a never before seen chromosomes that are a puzzle of the chromosomes of the mother and another never before seen chromosomes that are a puzzle of the chromosomes of father. I still can't find how common is the crossover, but in one link I got about 70 crossovers during the formation of the egg (with a lot of variations), that is approximately 3 crossovers per chromosome. I guess the crossover rate for the sperm is similar. There is an exception with the X and Y chromosomes in males, that can't crossover, so the Y chromosome is inherited without crossovers, and it's much easier to track the male ancestor line in the Y chromosome. See https://en.wikipedia.org/wiki/Y-chromosomal_Adam https://en.wikipedia.org/wiki/Y-chromosomal_Adam

13of40 8y ago

But those aren't differences in the same way that mutations are. The chromosomes passed on by the grandmother are identical to those received by the granddaughter, unless you're talking about spilicing genes between chromosomes. The morphological differences in the daughter are from the genes being expressed differently in the context of her body and the father's DNA. (Or so 90's science class would have me believe.)

gonvaled 8y ago
The daughter has some genes from the mother, and some from the father. Which genes are selected from which progenitor is random. To have a big pool for recombinations, inbreeding is to be avoided and populations must be big enough.
- ratacat 8y ago
  My cryptological brain can't herp but replace here... The "selected at random" with "selected in ways we don't understand"
  - HeadsUpHigh 8y ago
    There are parts of the cell that are noise-based. I'm talking about quantum level noise so in many ways it's as random as it gets.
- pygy_ 8y ago
  > Which genes are selected from which progenitor is random. IIRC that's not completely true. In mammal females, there is competition at the chromosome level to determine which member of each pair will end up in the first polar body (which is discarded) and which one ends up in the secondary oocyte (which then splits up to become the ovum and the secondary polar body).
gus_massa 8y ago
Each person has two chromosomes of each kind and they are mixed during the formation of the egg and sperms. For more details see https://en.wikipedia.org/wiki/Chromosomal_crossover https://en.wikipedia.org/wiki/Chromosomal_crossover So, ignoring mutations, the next generation gets a never before seen chromosomes that are a puzzle of the chromosomes of the mother and another never before seen chromosomes that are a puzzle of the chromosomes of father. I still can't find how common is the crossover, but in one link I got about 70 crossovers during the formation of the egg (with a lot of variations), that is approximately 3 crossovers per chromosome. I guess the crossover rate for the sperm is similar. There is an exception with the X and Y chromosomes in males, that can't crossover, so the Y chromosome is inherited without crossovers, and it's much easier to track the male ancestor line in the Y chromosome. See https://en.wikipedia.org/wiki/Y-chromosomal_Adam https://en.wikipedia.org/wiki/Y-chromosomal_Adam