Hi I was hoping someone could explain why meiosis makes 2 haploid cells then 4 haploid cells. Why are the first 2 cells after meiosis 1 not diploid. After splitting the two cells how can the 4 cells also be haploid??
I'm really confused by this
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why does meiosis make 2 haploid cells then 4 haploid cells? watch
- Thread Starter
- 09-11-2018 15:41
- 09-11-2018 15:51
The gamete mother cell replicates the DNA as normal. When the Chromosomes line up at the equator they do so in pairs rather than singles, which stops them from being pulled apart. Each pole then has a haploid number as the chromosomes haven’t been pulled apart. Once the cell splits into two they again line up and this time are pulled apart.
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.
- 09-11-2018 16:18
Meiosis was a really hard concept for me to grasp too, I find watching a you tube video helps to understand biology. Mr Pollock does amazing videos mainly focusing on AQA but I'm sure it's useful for other exam boards.
- 09-11-2018 17:27
I think the confusion is because in meoisis, we have differing amounts of DNA in the different stages which does not correspond to whether the cells are called "haploid" or "diploid". To explain step by step:
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")