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Definition of «Gonad»


Gonad: A reproductive gland (ovary or testis) that produces germ cells (gametes).

In embryonic life, the gonad in males and females is initially identical. This gonad is said to be "indifferent" before it differentiates into a definitive testis or ovary.

An indifferent gonad becomes a testis if the embryo has a Y chromosome, but if the embryo has no Y chromosome, the indifferent gonad becomes an ovary. Thus, an XY chromosome complement leads to testes while an XX chromosome complement leads to ovaries.

There are people with just one X chromosome and no Y. They are girls with Turner syndrome who are infertile. The absence of a Y chromosome permits the indifferent gonad to become an ovary. However, two X chromosomes are needed for the ovary to function normally.

The male gonad is the testicle (or testis), located behind the penis in a pouch of skin (the scrotum). The testicles produce and store sperm, and they are also the body's main source of male hormones (testosterone). These hormones control the development of the reproductive organs and other male characteristics, such as body and facial hair, low voice, and wide shoulders.

The word "testis" is Latin for "witness." In ancient times, a person providing testimony might validate it by holding the scrotum, his or another man's. "And the servant put his hand under the thigh of Abraham his master, and swore to him concerning the matter." (Genesis 24:9)

The female gonad, the ovary or "egg sac", is one of a pair of reproductive glands in women. They are located in the pelvis, one on each side of the uterus. Each ovary is about the size and shape of an almond. The ovaries have two functions: they produce eggs (ova) and female hormones.

Each month, during the menstrual cycle, an egg is released from one ovary. The egg travels from the ovary through a fallopian tube to the uterus.

The ovaries are the main source of female hormones (estrogen and progesterone). These hormones control the development of female body characteristics, such as the breasts, body shape, and body hair. They also regulate the menstrual cycle and pregnancy.

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