Eggs (also called ova or oocytes), and sperm are called "Sex Cells". A single egg cell is called an ovum, and a single sperm cell is called a spermatozoa.
The process of producing sperm or eggs is called meiosis. Readers who have some background knowledge in biology may recognize a similar term: "mitosis". Mitosis is the separation of a cell into two new cells, each with a complete set of DNA.Mitosis is in other words somatic. In meiosis, however, the resultant cell has only half the necessary DNA: 23 chromosomes, one from each pair. During conception, the 23 chromosomes from the sperm and the 23 chromosomes from the egg are combined to create a human fetus with 46 chromosomes.These are also called body cells.
Sperm are produced in vast quantities in the testicles, and sperm production is a constant cycle in the body. One of the 23 chromosomes in a sperm cell may be shaped slightly differently than the rest - this is referred to as a Y chromosome. A sperm cell with all 23 chromosomes the same shape is said to have an X chromosome. A child resulting from fertilization of an egg by a sperm with an X chromosome will be female, and a child resulting from fertilization of an egg by a sperm with a Y chromosome will be male.
There are sperm-sorting processes available to increase the likelihood of a particular sex for couples using intrauterine insemination to achieve pregnancy. Some in vitro fertilization clinics offer couples the option of sex testing before choosing which embryos to transfer. For couples seeking pregnancy the traditional way, however, there is no way to control which type of sperm fertilizes the egg.
Egg cells are released from the ovaries, usually one or two per menstrual cycle. Every egg has an X chromosome.
During fetal development, a female fetus will have developed between 6 and 7 million eggs by the fourth or fifth month of pregnancy. Most of the eggs gradually waste away; by puberty, the average female has 300,000 eggs remaining. During menopause, the body stops releasing egg cells.
Fertilization, also called conception, happens when a sperm cell combines with an egg cell, usually in the uterus. Once the first sperm enters the egg, the egg's cell membrane solidifies, to prevent multiple sperm from entering.
As the egg cell begins to divide, it is called a zygote.
Typically, fertilization occurs in the fallopian tubes. For couples that need to use in vitro fertilization to achieve pregnancy, fertilization occurs in a laboratory, and the resulting embryos are later placed in the uterus.