The diploid number is the number of chromosomes required for two complete copies of the organism’s genome (the entirety of its genetic information). In animals, this is the number of chromosomes in most cells (gametes being an important exception).
The DNA comprising the genome of a species is organized and packaged into complex structures called chromosomes. Eukaryotes characteristically possess multiple linear chromosomes.
The number of chromosomes in a complete genome is known as the haploid number. Sexual reproduction involves an alternating process of haploid to diploid back to haploid cells.
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Mitosis is the process of cell division that leads to daughter cell having the same number of chromosomes as the parent cell. A diploid parent cell produces two diploid daughter cells.
Meiosis is the process of cell division leading to the production of gametes. A diploid parent cell divides into four haploid daughter cells.
Fertilization of a haploid sperm cell with a haploid ovum produces a diploid zygote (fertilized egg). In humans, the egg and sperm each have a haploid number of 23 chromosomes. When a sperm fertilizes an egg, the resulting diploid zygote has 46 chromosomes (two sets of 23 chromosomes).
Some eukaryotes possess more than two copies of their genome in their cells. These multiple copies are referred to as polyploidy.