Sexual Reproduction involves in the formation of male and female gametes in either the same individual or two individuals. These gametes fuse to form a zygote which develops into a new individual. Offsprings are not identical to other one or to the parents.
Two stages of organisms:
1. Juvenile phase − Period of growth; non reproductive
2. Vegetative phase or reproductive phase
In non-primate mammals like rats, sheep, dogs, cows, tigers, etc, the cyclic change in the activities of the ovaries and the oviduct is called the oestrus cycle.
In primates like monkeys, apes and humans, it is called the menstrual cycle.
Few mammals are called continuous breeders because they can reproduce while some are called seasonal breeders because they can reproduce only in the favorable seasons.
Events in Sexual Reproduction :
1. Pre-Fertilization events
2. Fertilisation events
3. Post-Fertilisation events