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Human ova grow from primitive germ cells that are embedded in the substance of the ovaries. [10] The ovum is one of the largest cells in the human body, typically visible to the naked eye without the aid of a microscope or other magnification device. [11] The human ovum measures approximately 120 μm (0.0047 in) in diameter. [12]
Gametes of both mating individuals can be the same size and shape, a condition known as isogamy. By contrast, in the majority of species, the gametes are of different sizes, a condition known as anisogamy or heterogamy that applies to humans and other mammals. The human ovum has approximately 100,000 times the volume of a single human sperm cell.
Anisogamy is the form of sexual reproduction that involves the union or fusion of two gametes which differ in size and/or form. [12] The smaller gamete is considered to be male (a sperm cell), whereas the larger gamete is regarded as female (typically an egg cell, if non-motile).
In cellular biology, a somatic cell (from Ancient Greek σῶμα (sôma) 'body'), or vegetal cell, is any biological cell forming the body of a multicellular organism other than a gamete, germ cell, gametocyte or undifferentiated stem cell. [1] Somatic cells compose the body of an organism and divide through mitosis.
Photograph of an adult female human, with an adult male for comparison. (Both models have partially shaved body hair to show anatomy, i.e., clean-shaven pubic regions.) A distinguishing characteristic of the class Mammalia is the presence of mammary glands. Mammary glands are modified sweat glands that produce milk, which is used to feed the ...
Brain size is known to differ between men and women, for example (men on average have larger bodies than women), but without well documented differences in IQ. [46] A 2017 study found that the brains of women have a higher density of grey matter , which could compensate for the loss of volume.
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In mammals, the nucleolus of the oocyte is derived solely from maternal cells. [22] The nucleolus, a structure found within the nucleus, is the location where rRNA is transcribed and assembled into ribosomes. While the nucleolus is dense and inactive in a mature oocyte, it is required for proper development of the embryo. [22]