Sexual Reproduction: Post-Fertilisation Events
Events taking place after fertilisation process are called post-fertilisation events.
# The haploid gametes fuse to form a diploid zygote in all organisms.
# In external fertilisation, a zygote is formed in an external medium, and in internal fertilisation, a zygote is formed inside the individual.
# The development of a zygote depends upon the life cycle of an organism. In some organisms, the zygote does not develop immediately and develops a thick wall around itself. This wall is resistant to damage and desiccation.
# It is the process of development of the embryo from the zygote.
# The zygote undergoes cell division and differentiation.
# Cell division increases the number of cells of the embryo, and cell differentiation helps the cells undergo
modifications to form specialized tissues and organs.
# Animals can be grouped into two categories based on how and where the development of the zygote takes place. These categories are:
1. Oviparous − The fertilized egg is covered by a calcareous shell and is released into the outside environment. The development takes place inside the egg and the young one hatches out (example: birds and reptiles).
2. Viviparous − The development of the zygote takes place inside the female body, and the developed young one is delivered outside (example: mammals, including humans).
# In flowering plants, the zygote is formed inside the ovule.
Zygote → Develops into → Embryo
Ovule → Develops into → Seed
Ovary → Develops into → Fruit → Contains → Seeds → Disperse and germinate to form new plants