Post -fertilisation events- formation of zygote

Zygote. One celled , diploid, vital link between two generations.

•  External fertilization –zygote formed in external medium water

eg. Frog,

•  Internal fertilization –zygote formed inside the body eg. Humanbeings. Development of zygote depends on type of life cycle and environment. Some develop thick wall ( prevent damage and desiccation) & undergo period of rest

eg. Algae, fungi.

•  Haplontic life cycle- zygote (2n) divides by meiosis to form haploid (n) spores.

•  Diplontic life-cycle- zygote (2n) divides mitotically, develops into embryo (2n).

•  Oviparous animals lay eggs out-side the female body.Eggs can be fertilized/ unfertilized. Fertilized eggs covered which hard calcareous shell, laid in safe place in the environment. Unfertilised eggs laid in water.

Example- fishes, frogs, reptiles, birds 

• Viviparous animals bear and rear the embryo inside female body, give birth to young-ones.

Advantage- proper embryonic care, protection, survival chances of young-ones greater.

Example- cows, whales, humanbeings

• Embryogenesis: development of embryo from zygote by cell division (mitosis) and cell differentiation.