How does chromosome number get halved in meiosis I?

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In summary, during meiosis 1, the cell undergoes interphase and possibly S-phase, resulting in a 4n cell with 92 chromosomes. During anaphase 1, the chromosomes split and create two daughter cells with 46 chromosomes each. This is why, despite the initial doubling of chromosomes, the chromosome number is ultimately reduced in meiosis 1. This is different from mitosis, where the number of chromosomes remains the same.
  • #1
navneet9431
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In meiosis 1, it is said that chromosome numbers become halved in the two daughter cells.
For example, in a 2n human cell there are 46 chromosomes.
During meiosis 1, the cell will undergo interphase and probably the S-phase, where chromosome number becomes duplicated.
Now the cell is 4n (i.e. 92 chromosomes). During anaphase 1, 46 chromosome out of 92 would go towards one pole and 46 would go opposite.
Thus the resulting two cells will have 46 chromosomes in each. So why should we say that, in meiosis 1, the chromosome number is reduced?
 
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  • #2
navneet9431 said:
During meiosis 1, the cell will undergo interphase and probably the S-phase, where chromosome number becomes duplicated.
Now the cell is 4n (i.e. 92 chromosomes).

The stages before meiosis are similar to those of interphase before mitosis. The number of chromosomes does not double before meiosis I. Before meiosis I, the number of chromosomes remains the same, but each chromosome doubles the number of its chromatids.

http://cyberbridge.mcb.harvard.edu/mitosis_4.html
http://cyberbridge.mcb.harvard.edu/mitosis_6.html
 

1. What is the purpose of halving the chromosome number in meiosis I?

The purpose of halving the chromosome number in meiosis I is to ensure the production of gametes with the correct number of chromosomes. This is important for sexual reproduction and the formation of genetically diverse offspring.

2. How does the chromosome number get halved in meiosis I?

In meiosis I, homologous chromosomes pair up and exchange genetic material through a process called crossing over. Then, the homologous chromosomes separate, resulting in two cells with half the original number of chromosomes.

3. What is the difference between chromosome number halving in meiosis I and mitosis?

The main difference is that meiosis I results in cells with half the original number of chromosomes, while mitosis produces cells with the same number of chromosomes as the parent cell. Meiosis I also involves the exchange of genetic material between homologous chromosomes, which does not occur in mitosis.

4. Can the chromosome number get halved in a different phase of meiosis?

No, the halving of the chromosome number only occurs in meiosis I. In meiosis II, the sister chromatids of each chromosome separate, resulting in four cells with the same number of chromosomes as the parent cell.

5. What happens to the extra chromosome in individuals with chromosomal abnormalities?

In individuals with chromosomal abnormalities, the extra chromosome may not get halved during meiosis I. This can result in gametes with an incorrect number of chromosomes, leading to genetic disorders such as Down syndrome.

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