Kalthoff, Klaus O. School of Biological Sciences, University of Texas, Austin, Texas.
Last reviewed:December 2020
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- Structure of eggs and sperm
- Attraction of sperm to eggs
- Sperm–egg adhesion
- Gamete fusion
- Egg activation
- Blocks to polyspermy
- Related Primary Literature
- Additional Reading
Fusion of a female gamete (egg) with a male gamete (sperm) to form a single cell, termed a zygote. Fertilization in animals is a biological process that involves a sperm (male gamete) merging with an egg (female gamete or ovum) [Fig. 1] and leading to the development of an embryo. Gametes (germ cells or sex cells) are haploid because their nuclei contain only one set of chromosomes. In contrast, most animal cells are diploid because their nuclei contain two sets of chromosomes—one set derived from the egg and the other set derived from the sperm. Reduction from the diploid to the haploid number occurs in a specialized set of two cell divisions, known as meiosis, during which gametes are formed in the gonads of an adult. Fertilization restores the diploid chromosome number. In humans, normal eggs and sperm contain 23 chromosomes each. In contrast, the zygote and most of its daughter cells contain 23 pairs of chromosomes, or 46 chromosomes in total, per cell nucleus. See also: Cell division; Cell nucleus; Chromosome; Gametogenesis; Meiosis; Ovum; Sperm cell
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