Sexual Reproduction in Mammals

Overview

Sexual reproduction requires two parents, each providing half the genetic material to produce a genetically unique offspring.
The two types of sex cells or gametes are sperm (from the male) and eggs or ova (from the female).
Each gamete contains only one set of chromosomes (haploid), which is half the normal number of chromosomes found in body cells (diploid).
Gametes are produced by the process of meiosis, which ensures genetic diversity in the offspring.

Male Reproductive System

The male reproductive system includes the testes, penis, prostate gland, seminal vesicle, and vas deferens.
The testes produce sperm and testosterone. They are located in the scrotum for temperature control.
Sperm is created through spermatogenesis a form of meiosis taking place in the seminiferous tubules in the testes.
Maturing sperm are stored in the epididymis before being transferred via the vas deferens during ejaculation.
Semen, the fluid that contains sperm, is made up of secretions from the prostate gland and seminal vesicles.

Female Reproductive System

The female reproductive system consists of the ovaries, fallopian tubes, uterus, and vagina.
The ovaries produce the female gametes (ovum or egg cells) and the hormones oestrogen and progesterone.
Each month, typically one egg is released from the ovary in a process called ovulation, and enters the fallopian tube.
Fertilisation usually occurs in the fallopian tube. If the egg is fertilised, it travels to the uterus and implants in the endometrium (uterine lining) for development.
If fertilisation does not occur, the egg and the endometrium are discarded during menstruation.

Fertilisation and Embryo Development

Fertilisation is when a sperm cell penetrates an egg cell, and their genetic material combines to create a zygote with a full set of chromosomes.
The zygote undergoes cleavage - a series of rapid cell divisions.
This ball of cells becomes an embryo when it implants in the uterus.
Germ layers, the precursors to all future tissues and organs, are formed through the process of gastrulation.
The embryo continues to grow and develop, eventually forming a foetus.

Pregnancy and Birth

The placenta allows exchange of nutrients, oxygen, and waste products between mother and embryo/foetus.
Hormones like human chorionic gonadotropin (hCG), progesterone and oestrogen play vital roles in maintaining pregnancy.
Labour involves a series of strong, rhythmic contractions of the uterus which push the baby out through the vagina.
After birth, the placenta is also expelled from the uterus.