why does meiosis make 2 haploid cells then 4 haploid cells?Watch this thread
I'm really confused by this
When the chromosomes are moved the first time both chromatids are still joined at the centromere, which means it is still one chromosome. It is also worth noting at this point they have crossing over at points called chiasmata, and they independently line up (independent assortment).
You should be able to see it all from just googling meiosis and following a diagram.
At interphase prior to the first division, each chromosome in the mother gamete cell is a single strand of DNA (total amount of DNA in the cell = 2c, total number of chromosomes = 2n or 'diploid')
Then all the DNA strands replicate, but the doubled strands remain connected at the centromere, so they are still considered to be one chromosome and the cell is still 'diploid'. (total amount of DNA in the cell = 4c, but chromosomes still = 2c)
At prophase, sister chromosomes pair up and crossing over between the four strands of DNA takes place
During anaphase, the sister chromosomes separate again, one going to one pole and the other to the opposite pole. When the first division takes place, we then have one daughter cell with one of the pair of the sister chromosomes whilst the other sister goes to the other duaghter cell. Each chromosome is still made up of a double strand of DNA, but it is still considered as a single chromosome. Because the sister chromosomes have gone to different daughter cells, each daughter cell now has 2c of DNA but only 1n chromosomes = 'haploid')
In the second meoitic division, the two strands of DNA that make up each chromosome are split apart. One goes to one of the second generation of daughter cells, the other to another. Each duaghter gamnete cell now has a single strand of DNA and a single representative of each chromosome (DNA = 1c, chromosomes still = 1 n = haploid)
Afterr fertilisation, of course, each haploid gamete is fused with another haploid gamete so that we get a zygote cell with DNA = 2c and chromosome number 2n = 'diploid")