Yes, the chromosome number in the zygote, embryonal cells, and the adult organism of a particular species is generally constant. This constancy is primarily maintained through mitosis, where daughter cells inherit an identical copy of chromosomes from the parent cell, ensuring the number of chromosomes remains the same across all stages of development.
Here’s a more detailed explanation:
Zygote:
The zygote is formed by the fusion of haploid gametes (sperm and egg), each carrying half the species’ chromosome number. This fusion restores the diploid number, creating a cell with the species’ characteristic chromosome number.
Embryonal Cells:
During embryonic development, cells divide through mitosis, resulting in daughter cells that are exact copies of the original zygote. This process maintains the chromosome number in the developing embryo.
Adult Organism:
Similarly, all somatic cells (body cells) in the adult organism also undergo mitosis, ensuring the consistent chromosome number throughout the organism’s tissues and organs.
Key Point: The exception to this rule is the formation of gametes (sperm and egg) through meiosis. Meiosis reduces the chromosome number by half, ensuring that the fusion of gametes at fertilization restores the correct number for the zygote.