Do chromosomes grow?

[匿名]

2016-03-15 11:58 pm

更新1:

Humans have 23 pairs of chromosomes containing some 3 billions of "base pairs" each. Primates have 24 pairs of chromosomes, mice have 20 and worms have 4 pairs only. Do those 4 pairs in worms contain the same number of nucleotids, only differently distributed, chromosomes having seperated during the process of evolution, thus increasing in numbers, or do lower species' cell nucleus contain lower amounts of nucleotids (less DNA), meaning: DNA content increases during evolution?

回答 (2)

Amy

2016-03-16 12:05 am

No, they actually shrink! Every time a cell divides, it splits its DNA down the center and then fills in the opposite side by base-pairing symmetry. But most cells can't fill in the ends, so with each cell division the chromosome gets a little smaller. The exception is germ-line cells, which have a special enzyme for replicating the ends of DNA.

Re update:
Mammals have more nucleotides than worms. Humans and apes have pretty much identical DNA, with two ape chromosomes fused into one long human chromosome.
More nucleotides doesn't always mean more functional genes. Sometimes plants just double all their DNA and become a new species. Evolution is probably slowly removing this excess DNA.

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[匿名]

2016-03-15 11:59 pm

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