Sexual Reproduction: How does a sperm and egg form a baby?

Once a month, following ripening, a single egg is released from a woman's ovaries during the menstrual cycle, with the hope of fertilisation. During the act of sexual reproduction, the father's sperm is deposited within the mother's vagina in order to penetrate this egg. The sperm use their powerful tails to propel towards the egg, and release enzymes to break down its protective coat. It is essential that only one sperm enters the egg, as only two gametes (1 egg and 1 sperm) can contribute to forming a healthy child. The maternal and paternal DNA is mixed within the egg, and the nucleus of this first combined cell forms. This cell then goes on to divide and multiple in order to form a zygote. Over 9 months this ball of cells develops the features of a foetus whilst in the mother's womb and relies upon maternal nutrients and oxygen to survive. As a result of this amazing biological phenomenon every individual possesses DNA which comes in equal parts from both their mother and father. Which genes we received from which parent depends on properties of meiosis and mitosis, such as independent assortment; topics to be covered in a further genetics tutorial. 

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