the behavior of chromosome sets in the human life cycle. The human life cycle begins when a haploid sperm cell fuses with a haploid ovum. ○ The union of these gametes, culminating in the fusion of their nuclei, is fertilization . The fertilized egg (zygote) is diploid because it contains two haploid sets of chromosomes bearing genes from the maternal and paternal family lines. As a person develops from a zygote to a sexually mature adult, mitosis generates all the somatic cells of the body. ○ Each somatic cell contains a full diploid set of chromosomes. Gametes, which develop in the gonads (testes or ovaries), are not produced by mitosis. ○ If gametes were produced by mitosis, the fusion of gametes would produce offspring with four sets of chromosomes after one generation, eight after a second, and so on. Instead, gametes undergo the process of meiosis, in which the chromosome number is halved. ○ Human sperm or ova have a haploid set of 23 different chromosomes, one from each homologous pair.
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