Biology · Development of organisms and continuity of life. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Chromosomes are found in the nucleus. They contain DNA, which carries genetic information as genes. A diploid nucleus has two sets of chromosomes, so there is a pair of each type. Human body cells are diploid, with 23 pairs (46). A haploid nucleus has one set. Gametes are haploid, with 23.
Mitosis is nuclear division that gives genetically identical cells with the same chromosome number. It is used for growth, repair of damaged tissues, replacement of cells and asexual reproduction. Stem cells are unspecialised cells that divide by mitosis, and their daughter cells can become specialised.
Meiosis makes gametes. It is a reduction division: the chromosome number is halved from diploid to haploid, and the cells are genetically different. Cancers form when cell division is uncontrolled.
Students give the halved number for mitosis. Mitosis keeps the number the same; only meiosis halves it.
Answer: Sperm cell 32, zygote 64, skin cell of the foal 64.
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