Animal Reproduction

In biology, reproduction is the mechanism that produces new generations and offspring; animals have two primary mechanisms - sexual and asexual reproduction.

Sexual Reproduction

Sexual reproduction involves the fusion of male and female gametes (sex cells) to create offspring with a genetic mix of both parents.
Gametes are formed by a specific type of cell division called meiosis. In this process, chromosome numbers are halved, which allows the fusion of gametes to result in offspring with the correct number of chromosomes.
Animals exhibit various methods of sexual reproduction including live birth, egg laying, and spawning.
During fertilisation, the male gamete (sperm) and female gamete (egg or ovum) combine, sharing their genetic material to form a zygote which develops into an embryo.
The fertilisation process can happen internally (inside the body) as in mammals or externally (outside the body) as seen in many fish and amphibians.

Asexual reproduction is the process by which offspring arise from a single parent, and inherit the genes of that parent only. Hence, the offspring are genetically identical, forming clones.
Common methods of asexual reproduction in animals include binary fission, budding, fragmentation, and parthenogenesis.
In binary fission, an organism splits into two separate individuals; budding involves growth of a new individual from a part of the parent organism.
Fragmentation occurs when a parent breaks into pieces and each piece can develop into a new organism, while parthenogenesis is the development of an egg into an individual without fertilisation.

Sexual dimorphism refers to the physical differences between male and female individuals of the same species, other than their reproductive organs. It can range from size, colouration, to specific physical features.
Gender determination in animals could be the result of genetic factors (like in mammals where it’s determined by X and Y chromosomes), environmental factors (as in some reptiles, where it’s temperature-dependent), or social factors (as in clownfish, where the dominant female dies, the male changes gender to female).

The life cycle of an animal includes all the stages from the end of the last generation to the beginning of the next.
Life cycles vary greatly among animals and can include stages of development such as egg, larva, pupa, and adult.
Some animals undergo metamorphosis, a process of significant and rapid transformation in the animal’s body structure, during their life cycle.
Many insects display complete metamorphosis with four life stages: egg, larva, pupa (during which the transformation occurs), and adult. Whereas, many amphibians exhibit incomplete metamorphosis where the young (like tadpoles) resemble the adults but lack sexual maturity.