The Cellular Basis of Reproduction
Read this introduction to sexual reproduction. Each organism of a mating pair gives half of their chromosomes to their offspring. Pay special attention to the definition of haploid and diploid cells. As you read, consider how sexual reproduction benefits a species by creating diversity.
Figure 10.1 A sea urchin begins life as a single diploid cell (zygote) that (a) divides through cell division to form two genetically identical daughter cells, visible here through scanning electron microscopy (SEM). After four rounds of cell division, (b) there are 16 cells, as seen in this SEM image. After many rounds of cell division, the individual develops into a complex, multicellular organism, as seen in this (c) mature sea urchin.
A human, like every sexually reproducing organism, begins life as a fertilized egg (embryo) or zygote. In our species, billions of cell divisions subsequently must occur in a controlled manner to produce a complex, multicellular human comprising trillions of cells. Thus, the original single-celled zygote is literally the ancestor of all cells in the body. However, once a human is fully grown, cell reproduction is still necessary to repair and regenerate tissues and sometimes to increase our size! In fact, all multicellular organisms use cell division to grow, maintain, and repair cells and tissues. Cell division is closely regulated, and the occasional failure of this regulation can have life-threatening consequences. Single-celled organisms may also use cell division as their method of reproduction.
Source: OpenStax, https://openstax.org/books/biology-2e/pages/10-introduction
This work is licensed under a Creative Commons Attribution 4.0 License.