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  • Is the chromosome number of zygote, embryonal cells and adult of a particular organism always constant? How is the constancy maintained in these three stages?

Is the chromosome number of zygote, embryonal cells and adult of a particular organism always constant? How is the constancy maintained in these three stages?

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Yes, the chromosome number of the zygote, embryonal cells and adult of a particular organism is always constant. Sexual reproduction includes gamete formation through meiosis and fertilization. Meiosis reduces the number of chromosomes to half in male and female gametes. This reduced chromosome number is then restored to normal during fertilization of male and female gametes. A zygote is formed by the fusion of gametes.

Once formed, it undergoes mitotic divisions. Embryonal cells also divide by mitosis to produce more of its kind. The cells in the adult organism also divide by mitosis. Hence mitosis in gamete formation and fertilization together maintain the chromosome number in the zygote. Embryo and adult form is formed from zygote by mitosis division (equational division).

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