POST- FERTILIZATION EVENTS

Zygote formation

• In some organisms like fungi and algae, the zygote develops a thick wall around it which is resistant to damage and undergoes a period before germination.
• Further development of zygote depends on the type of life cycle of organisms and the environment in which they are surviving.
• In all sexually reproducing organisms, a diploid zygote is formed as a result of fertilization and later the zygote develops into a new organism.

Embryogenesis

• The process of development of embryo from the zygote is called embryogenesis.
• Embryogenesis includes cell division and cell differentiation in the zygote.
• Cell division increases the number of cells and cell differentiation helps to form tissues and organs to form a fully developed organism.

Fig. embryogenesis

•  Depending on the development of zygote inside or outside the body of the female parent, animals are classified into oviparous and viviparous animals.
• Oviparous animals are those which lay eggs and the eggs develop into new organisms. Example- amphibians, fishes, birds, reptiles etc.
• Viviparous animals are those which give birth to their young ones. Example- mammals.
• In some oviparous animals like reptiles and birds the fertilized eggs remain covered by hard calcareous shell and such eggs are called cleidoic
• In flowering plants, the zygote is formed inside the ovule and the sepals, petals, stamens of the flower usually fall off.
• The zygote develops into embryo
• Ovules develop into seeds
• The ovary develops into the fruit.
• The ovary wall develops into a protective layer called pericarp.

Fig. fruit and seed formation