mitoses and meioses in cannabis spawn production

[hedgeraider]

i was surprised to find that cannabis gametes are made by mitosis and not by meiosis, meiosis is recombinating genes like in human reproduction, and mitoses is the same as body cell division, so that all the pollen is the same genetics as the father and as each other, prettymuch. so breeding mum and dad plants supposedly makes 100 percent the same offspring?

sounds mental.

 

[hedgeraider]

does anyone have any thoughts on this? It's as if you and your wife made 5 identical twins because all your babies were the same. I think cannabis must have some way of mixing up the offspring so they are different, there must be some kind of recombination of genes.

 

[Torched]

Well I'm no geneticist, but I play one on the intertubes. Any offspring should be a 100% copy of their parents genetic code. However those genetic blueprints can express themselves in a huge variety of different ways. Which is why you are not the twin of your sibling despite caring the same genes.

 

[Waira]

Hedge]- ..had to dust off the ol' botany book for this one.... Yes, all plants do have a meiosis phase in the sex cell reproduction, but it's different process than it is for animals... Details are kinda complex, so I'll stick to the broad strokes here. Firstly, a cell with it's normal chromosomal count is said to be diploid, designated as 2n, while sex cells, or gametes, have half the normal amount, called haploid, designated as n,... In mitosis, the chromosomes are replicated as they are, xeroxed if you will, simply copied and separated as the rest of the cell divides, they're not divided in half (to a haploid state, or n), that type of division is part of meiosis only... mitosis doesn't change the chromosome amount, but as you'll see below, a haploid cell can undergo mitosis, basically to simply make more haploid cells (think zillions of pollen grains, all haploid); in meiosis, chromosomes are arranged differently, and most importantly, there is an event called "cross-over" where there is some swapping of chromosomal segments, and this is how the genetics get scrambled enough to form natural variation, instead of just forming the same ol' thing as in mitosis; also there is a further division step that reduces the cell chromosome to the haploid, or n state....In plants, this is taking place in specialized mother cells, resulting in spore cells that are haploid... these don't fuse with each other (not sperm and egg yet basically), but then undergo mitosis that replicates themselves and still keeps them haploid (I know it's a bit confusing, and there's much more detail to this... that's why there are whole chapters of info in textbooks about this); all the cells then form a multicellular gametophyte, 2 kinds, that will then make single cell gametes, the haploid sperm (found in pollen) and egg ( in female flowers)..... these final gametes are what finally fuse to form the zygote (2n),.... quiz Monday! I hope this makes some sense... keep in mind animal gametes take a different path when forming gametes, but the end result (n) is the same...

 

[hedgeraider]

Waira, Thanks that is clearer now! i have to find info on genetic recombination of gametes and expression of the male and female parent cells of the plants. there may be chapters and chapters about the expression of the haploid genes, it could be interesting. will have to find some solutions...

So it would appear that the parent cells that make the seed-pod fuse and start to devide and grow on the mother, and perhaps there is some swapping of chromosomes in the mitosis after the chromosomes have joined into normal cells and the do growth cell divisions. the pollen is all twins! it's very surprising, probably the ovary cells are also composed of twins. ill see if i can find a book on it.

 

[sunkist]

The female does in fact undergo meiosis in production of the embryo. before becoming the embryo, the haploid n cells do undergo mitosis, where only one of the resulting mitotic products will become the egg, and the other ones will become endosperm in the egg (the white stuff comprising most of the inside of the seed).

And yes, the pollens are "twins", but they are also products of meiosis. One fo these makes the zygotic element (the part that will actually develop into the plant), and the other one will combine with the remaining (non-egg) bits in the embryo to make the endosperm, which will act as food for the sprout.

This is all basic botany. I would recommend the Raven Biology of Plants. A very cool university textbook you can probably download somewhere for free.