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Animal breeding is the controlled reproduction of an animal usually in order to improve certain traits or qualities (Freeman 2019). The mammals reproduce by means of sexual reproduction and the majority give birth to live young (Hardwood and Wilkin 2019) What this means is that sperm cell from a male is used used to fertilize the egg cell, or ova ( Nature Education 2014), from a female to create what is called a zygote ( National Geographic Society 2019). The sperm in and the egg are also referred to sex cells or gametes and they are produced in the testes or ovaries respectively (Nature Education 2014).

The processes for creating a gamete is called miosis. During miosis cells from the parent animal divide and produce gametes with half the chromosomes. Parents cells with a full set of chromosomes are called diploid Cells, the newly formed gametes are haploid cells because they contain half the chromosome material Nature Education (2014) .

This is important because when the gametes combine during sexual reproduction they create a new cell with a complete set of chromosomes. That cell is called a zygote and this single cell is the beginning of a new animal (need citation). In the early stages of development the cell, and later group of cells, is often referred to as an embryo (citation needed) and later in its development it may be referred to as a fetus (Citation needed).

After birth some species produce offspring that are precocial meaning they are well formed at the time of birth. Other species, including mice, are altricial, meaning that they are underdeveloped and mostly helpless at the time of birth (need citation)

Terms to be discussed: Neonate, Litter, Nest, nursing, stages of development, pregnancy, Lordosis Behavior, Mounting Behavior, Exothermic, Endothermic


National Geographic (2019). Sexual Reproduction. Retrieved from

Nature Education (2014) Gametes. Retrieved from

Freeman, A. (2019) Animal breeding. Encyclopædia Britannica, inc. retrieved from

Hardwood, J., Wilkin, D. (2019) Mammal reproduction. ck-12. Retrieved from