How can an egg begin development without being fertilized during parthenogenesis?

In parthenogenesis, an egg begins development without fertilization through several distinct biological mechanisms, depending on the species:

• Automixis: A postmeiotic process where a haploid egg cell either duplicates its chromosomes or joins with another haploid cell to form a diploid zygote.1
• Apomixis: The egg bypasses complete meiosis. Instead, it is produced through mitosis, resulting in a diploid daughter cell that is a genetic clone of the parent.1
• Chromosome Doubling: In some species, such as certain wasps and water fleas, the egg undergoes a process of chromosome doubling, allowing it to develop into a female individual without the need for sperm.2
• Stimulation without Genetic Contribution: In pseudogamy (or gynogenesis), sperm is required only to trigger the initial development of the egg; the sperm's genetic material is not incorporated into the offspring.1
• Experimental Activation: In laboratory settings, unfertilized eggs can be induced to develop through artificial means, such as treating them with weak organic acids or mechanically pricking the egg surface with a needle.2