Final answer:
Zebrafish development begins with a single-cell zygote that undergoes mitosis to form many undifferentiated cells. The cells then differentiate into specialized types and arrange into layers during gastrulation to form various tissues and organs, thus creating a larval zebrafish.
Step-by-step explanation:
Scientists use zebrafish as a model organism to understand the complex processes of meiosis and cell differentiation because their development shares many basic biological processes with humans. A zebrafish starts its life as a zygote, which is a single cell formed by the fusion of sperm and egg. This zygote possesses a full genetic blueprint necessary for the development of a new organism.
After fertilization, the zygote undergoes a process called mitosis, a series of cell divisions that increase the number of cells without changing the total volume of the cell mass. This means that the zygote divides to form two cells, then four, eight, and continues exponentially. At a certain stage, cells start undergoing differentiation, a process in which cells become specialized in structure and function. Differentiation occurs as certain genes are activated while others are repressed, directing cells to develop into specific tissues and organs.