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The other product of meiosis is the second polar body with only chromosomes but no ability to replicate or survive. In the fertilized daughter, DNA is then replicated in the two separate pronuclei derived from the sperm and ovum, making the zygote's chromosome number temporarily 4n diploid.
By contrast, gametes of diploid organisms contain only half as many chromosomes. In humans, this is 23 unpaired chromosomes. When two gametes (i.e. a spermatozoon and an ovum) meet during conception, they fuse together, creating a zygote. Due to the fusion of the two gametes, a human zygote contains 46 chromosomes (i.e. 23 pairs). [citation needed]
The list of organisms by chromosome count describes ploidy or numbers of chromosomes in the cells of various plants, animals, protists, and other living organisms.This number, along with the visual appearance of the chromosome, is known as the karyotype, [1] [2] [3] and can be found by looking at the chromosomes through a microscope.
The zygote contains the combined genetic material carried by both the male and female gametes which consists of the 23 chromosomes from the nucleus of the ovum and the 23 chromosomes from the nucleus of the sperm. The 46 chromosomes undergo changes prior to the mitotic division which leads to the formation of the embryo having two cells.
In the first stage of sexual reproduction, meiosis, the number of chromosomes is reduced from a diploid number (2n) to a haploid number (n). During fertilisation, haploid gametes come together to form a diploid zygote, and the original number of chromosomes is restored.
Polyspermy results from multiple sperm fertilizing an egg, leading to an offset number of chromosomes within the embryo. [35] Polyspermy, while physiologically possible in some species of vertebrates and invertebrates, is a lethal condition for the human zygote.
During sexual intercourse, sperm cells are ejaculated into the vagina through the penis, resulting in fertilization of an ovum to form a zygote. [1] While normal cells contain 46 chromosomes (23 pairs), gamete cells contain only half that number, and it is when these two cells merge into one combined zygote cell that genetic recombination ...
Because the number of chromosomes is halved during meiosis, gametes can fuse (i.e. fertilization) to form a diploid zygote that contains two copies of each chromosome, one from each parent. Thus, alternating cycles of meiosis and fertilization enable sexual reproduction , with successive generations maintaining the same number of chromosomes.