Chromosome numbers and mitosis HELP!

[Wriggley]

Hello everyone I'm 26 and currently retaking my GCSE biology

 

Please could someone help me understand something about mitosis?

 

Body cells have 46 chromosomes

 

So why does both my GCSE science books talk about the parent cell in mitosis only having 4 chromosomes?

[Sriman Dutta]

Each human cell, except sex cells, consist of 23 homologous pairs of chromosomes. This is generally known as diploid. In a male it is shown by 44+XY and in a female it's 44+XX. Mitosis is quite simple. It only involves the replication of the nucleus and division of the parent cell into two identical daughter cells. There are basically four phases of mitosis - prophase, metaphase, anaphase and telophase. The final division occurs by cytokinesis. After cell division the young cells may temporarily enter into a resting phase or growth phase, during which sufficient chromatin material is synthesized. This continues repeatedly. The whole process is termed as cell cycle.

Now in case of meiosis which produces gametes, there are two phases - reduction division and the mitotic division. The reduction division is the division of a diploid cell into two haploid cells. Thus chromosome number is halved. Male gametes may have either 22+X or 22+Y, whereas female gametes have 23+X. This reduction phase is crucial as on fertilization the original 23 pairs are restored. Next comes the mitotic division in which each haploid cell further divides into two daughter cells.

[OldChemE]

Maybe the books are mixing something (a typo??) or you are misunderstanding. There are two types of cell division: Mitosis and Meiosis. Mitosis is the normal cell division (NOT sex cells). In Mitosis the parent cell duplicates its chromosomes first, then divides once, producing two identical cells having the same 46 chromosomes (called diploid cells). In meiosis (sex cells), the duplication of chromosomes happens once (like Mitosis) but the division process happens twice, producing 4 new cells, but each one only has 23 chromosomes (called haploid cells, or gametes). Thus, in Meiosis, one parent cell produces 4 sex cells. Could that be the 4 you are reading about??

[MonDie]

Number of chromosomes depends on the species as well as the cell type. It might be 4 in the example.

Edited March 30, 2017 by MonDie