Jennifer A. In humans, as in other mammals, sex determination depends on the testis, and testis differentiation depends on the Y chromosome. The event that marks human male determination is the differentiation of the testis at about 5 wk of gestation. The pivotal genetic event is the switching of the indifferent gonad the genital ridge to testis differentiation by the action of a gene called the testis-determining factor TDF. After this event, male development unfolds automatically, unless something goes wrong. A number of genetic accidents—anything from absence or mutation of TDF to a block of the action of testosterone—can interrupt the male-determining pathway, and when this happens, the phenotype of the baby is female.
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How many chromosomes do people have?: MedlinePlus Genetics
Chromosomes are thread-like molecules that carry hereditary information for everything from height to eye color. They are made of protein and one molecule of DNA, which contains an organism's genetic instructions, passed down from parents. In humans, animals, and plants, most chromosomes are arranged in pairs within the nucleus of a cell. Humans have 22 of these chromosome pairs, called autosomes. Humans have an additional pair of sex chromosomes for a total of 46 chromosomes. The sex chromosomes are referred to as X and Y, and their combination determines a person's sex.
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How many chromosomes do people have?
Metrics details. The recent sequencing of a large chunk of euchromatin from the human Y chromosome is a technical tour de force. It answers some evolutionary questions about this unusual chromosome while raising others. The Y chromosome is probably the most bizarre part of the human genome, reflecting its unique status as a huge block of largely non-recombining DNA, maintained in a permanently heterozygous state, and transmitted solely through males [ 1 ].
This page has been archived and is no longer updated. Whether an animal will become a male, a female, or a hermaphrodite is determined very early in development. Scientists have worked for hundreds of years to understand the sex-determination system. For instance, in B. If the male's heat could overwhelm the female's coldness, then a male child would form.