4 ms·

So in birds, sex chromosome arrangement is a reverse of what we have in humans. Their males are ZZ and the female is ZW. Which is why only males appear from thi

So in birds, sex chromosome arrangement is a reverse of what we have in humans. Their males are ZZ and the female is ZW. Which is why only males appear from this parthenogenesis.

rory 5y ago
> Which is why only males appear from this parthenogenesis Could you explain the mechanism? If the female has both chromosomes, why couldn't it produce offspring with both?
- smiley1437 5y ago
  The mostly likely path to parthenogenesis in a ZW female is making ZZ and WW offspring, and the WW is usually not viable. https://en.wikipedia.org/wiki/Parthenogenesis#Sex_of_the_offspring https://en.wikipedia.org/wiki/Parthenogenesis#Sex_of_the_off...
- semenko 5y ago
  The mechanisms of parthonenogensis aren't fully characterized, but at a high level, it occurs in a secondary oocyte during meiosis II -- the oocyte only starts out with a Z or W chromosome. It's perhaps best shown in this figure: https://rep.bioscientifica.com/view/journals/rep/155/6/images/REP-17-0728fig1.jpeg https://rep.bioscientifica.com/view/journals/rep/155/6/image... (Via this paper: https://pubmed.ncbi.nlm.nih.gov/29559496/ https://pubmed.ncbi.nlm.nih.gov/29559496/)
s1artibartfast 5y ago
If the females are ZW, why can't they make WW or ZW?
- simiones 5y ago
  ZW is less likely because normally parthenogenesis starts with a haploid egg cell (Z or W) that undergoes meiosis alone, copying its own chromosomes - becoming ZZ if it started as Z and WW if it started as W. WW is normally not viable, just like YY in mammals, so the most likely case of parthenogenesis by far is ZZ, male.
  - s1artibartfast 5y ago
    Thank you!
  - InvaderFizz 5y ago
    So in this case, the ZZ offspring is a genetic clone of its grandfather? That's the only sense I can make of it. No, wait, half clone. Yup, I'm fully confused by this turn of events.
    - sp332 5y ago
      It's a "clone" of half of the mother's DNA. The mother had random inheritance from its parents. So it's not a clone of the grandparents, but it's a copy of (half of the) mix that the mother had.
    - tsimionescu 5y ago
      No, it's more like an extreme case of in-breeding. On the other hand, if a mammal were to produce a viable fertile offspring through parthenogenesis, then that offspring would be a clone of it's mother.
      - tsimionescu 5y ago
        Meant to say: mammal mother produces a viable offspring through parthenogenesis, which in mammals would be XX, a daughter, an in-bred individual. Now, if that daughter produces another daughter through parthenogenesis, then this second generation of parthenogenesis individual would be a clone of the first generation daughter.
dredmorbius 5y ago
Right. From my very shallow understanding: - The fact that females are defined by unmatched sex chromosomes rather than matched ones means that in haploid parthenogenesis (a split and rejoining of a single half of a genome, rather than fertilisation by male and female sex cells), the resultant sex cells are either ZZ (vialble male) or WW (nonviable "super-female"). - Parthenogenesis in mammals on a similar basis isn't possible as the umatched chromsome is found in males (giving a viable XX female) ... but without an ovum or womb. A self-replicating female egg would be XX.[1] There's ... some research into parthenogenesis in mammals, and at least one apparent observed instance.[2] - In the case of Avian or similarly Z/W species, parthogenesis is a potentially viable option for resuming sexual reproduction of a population in which all males have been lost. For mammallian populations, not so much. In any case, there'd likely be an extreme genetic bottleneck. ________________________________ Notes: 1. Religious implications for spontaneous mammalian parthogenesis resulting in male offspring are left ... undiscussed. 2. See Google Scholar for a literature overview: https://scholar.google.com/scholar?hl=en&as_sdt=7%2C39&q=parthenogenesis+in+mammals&btnG= https://scholar.google.com/scholar?hl=en&as_sdt=7%2C39&q=par...
fortran77 5y ago
Was Jurassic park wrong then?

So in birds, sex chromosome arrangement is a reverse of what we have in humans. Their males are ZZ and the female is ZW. Which is why only males appear from this parthenogenesis.

rory 5y ago

> Which is why only males appear from this parthenogenesis Could you explain the mechanism? If the female has both chromosomes, why couldn't it produce offspring with both?

smiley1437 5y ago
The mostly likely path to parthenogenesis in a ZW female is making ZZ and WW offspring, and the WW is usually not viable. https://en.wikipedia.org/wiki/Parthenogenesis#Sex_of_the_offspring https://en.wikipedia.org/wiki/Parthenogenesis#Sex_of_the_off...
semenko 5y ago
The mechanisms of parthonenogensis aren't fully characterized, but at a high level, it occurs in a secondary oocyte during meiosis II -- the oocyte only starts out with a Z or W chromosome. It's perhaps best shown in this figure: https://rep.bioscientifica.com/view/journals/rep/155/6/images/REP-17-0728fig1.jpeg https://rep.bioscientifica.com/view/journals/rep/155/6/image... (Via this paper: https://pubmed.ncbi.nlm.nih.gov/29559496/ https://pubmed.ncbi.nlm.nih.gov/29559496/)

s1artibartfast 5y ago

If the females are ZW, why can't they make WW or ZW?

simiones 5y ago
ZW is less likely because normally parthenogenesis starts with a haploid egg cell (Z or W) that undergoes meiosis alone, copying its own chromosomes - becoming ZZ if it started as Z and WW if it started as W. WW is normally not viable, just like YY in mammals, so the most likely case of parthenogenesis by far is ZZ, male.
- s1artibartfast 5y ago
  Thank you!
- InvaderFizz 5y ago
  So in this case, the ZZ offspring is a genetic clone of its grandfather? That's the only sense I can make of it. No, wait, half clone. Yup, I'm fully confused by this turn of events.
  - sp332 5y ago
    It's a "clone" of half of the mother's DNA. The mother had random inheritance from its parents. So it's not a clone of the grandparents, but it's a copy of (half of the) mix that the mother had.
  - tsimionescu 5y ago
    No, it's more like an extreme case of in-breeding. On the other hand, if a mammal were to produce a viable fertile offspring through parthenogenesis, then that offspring would be a clone of it's mother.
    - tsimionescu 5y ago
      Meant to say: mammal mother produces a viable offspring through parthenogenesis, which in mammals would be XX, a daughter, an in-bred individual. Now, if that daughter produces another daughter through parthenogenesis, then this second generation of parthenogenesis individual would be a clone of the first generation daughter.

dredmorbius 5y ago

Right. From my very shallow understanding: - The fact that females are defined by unmatched sex chromosomes rather than matched ones means that in haploid parthenogenesis (a split and rejoining of a single half of a genome, rather than fertilisation by male and female sex cells), the resultant sex cells are either ZZ (vialble male) or WW (nonviable "super-female"). - Parthenogenesis in mammals on a similar basis isn't possible as the umatched chromsome is found in males (giving a viable XX female) ... but without an ovum or womb. A self-replicating female egg would be XX.[1] There's ... some research into parthenogenesis in mammals, and at least one apparent observed instance.[2] - In the case of Avian or similarly Z/W species, parthogenesis is a potentially viable option for resuming sexual reproduction of a population in which all males have been lost. For mammallian populations, not so much. In any case, there'd likely be an extreme genetic bottleneck. ________________________________ Notes: 1. Religious implications for spontaneous mammalian parthogenesis resulting in male offspring are left ... undiscussed. 2. See Google Scholar for a literature overview: https://scholar.google.com/scholar?hl=en&as_sdt=7%2C39&q=parthenogenesis+in+mammals&btnG= https://scholar.google.com/scholar?hl=en&as_sdt=7%2C39&q=par...

fortran77 5y ago

Was Jurassic park wrong then?