why do cells created by meiosis only have half the number of chromosomes from the original cell?
To keep the next generation from having double the species number of chromosomes.
Cells created by meiosis only have half the number of chromosomes from the original cell because meiosis is a specialized cell division process that produces gametes (sex cells) in sexually reproducing organisms. The reduction in the number of chromosomes ensures that when gametes fuse during fertilization, the resulting offspring will have the normal chromosome number.
During meiosis, there are two rounds of cell division: meiosis I and meiosis II. The number of chromosomes is halved during meiosis I. This is achieved through a process called homologous chromosome pairing and crossing over. Homologous chromosomes, inherited from each parent, come together and exchange segments of genetic material through crossing over. This genetic exchange results in genetic diversity in the gametes.
Following meiosis I, two haploid cells are formed, each containing half the number of chromosomes as the original cell. In humans, this means that the resulting cells have 23 chromosomes rather than the usual 46 found in somatic cells. These cells then proceed to meiosis II, where the sister chromatids are separated. This division results in the formation of four haploid cells, each with only one copy of each chromosome.
Overall, the reduction in chromosome number during meiosis is crucial for maintaining the correct chromosome number of a species in sexual reproduction and contributes to genetic diversity in offspring.