Animal Embryonic Development

Notes

• Subtopic: Introduction to Embryogenesis Embryogenesis is the process in which the genotype is expressed as the phenotype. During this process, all undifferentiated cells turn into specialized cells, creating different phenotypes in the body. According to the Recapitulation Theory, during embryonic development, organisms pass through stages that resemble features of their evolutionary ancestors. • Subtopic: Stages of Embryonic Development 1. **Fertilization** Fertilization is the initial stage where sperm penetration and membrane fusion occur. The egg cell has a protective coat that sperm cells must penetrate by releasing enzymes to reach the egg's plasma membrane. The fusion of the sperm and egg cell, each contributing 23 chromosomes, leads to egg activation. This activation involves the release of calcium ions, catalyzing protein production, establishing symmetry in the egg's cytoplasm, increasing metabolic activities and protein synthesis, completing meiosis to form haploid cells, and blocking the entry of additional sperm to avoid polyploidy. Humans are diploids, and having too many chromosomes can lead to diseases, although some organisms like salamanders and plants b...