Heredity

A trait is heritable when identical twins are more like each other than fraternal twins.

Heredity is the passing of traits (characteristics) from parents to offspring. In biology, the study of heredity is called genetics. With most living things, heredity is analysed by breeding (making crosses), often in a laboratory. But with humans, heredity is studied in other ways. Family pedigrees, identical twins and DNA genome analysis all provide clues.

A trait which may be inherited is heritable; it is inborn or innate.

Heredity Media

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  Heredity of phenotypic traits: a father and son with prominent ears and crowns.

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  DNA structure. Bases are in the centre, surrounded by phosphate–sugar chains in a double helix.

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  Aristotle's model of inheritance. The heat/cold part is largely symmetrical, though influenced on the father's side by other factors, but the form part is not.

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  Table showing how the genes exchange according to segregation or independent assortment during meiosis and how this translates into Mendel's laws

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  An example pedigree chart of an autosomal dominant disorder.

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  An example pedigree chart of an autosomal recessive disorder.

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  An example pedigree chart of a sex-linked disorder (the gene is on the X chromosome).

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  Hereditary defects in enzymes are generally inherited in an autosomal fashion because there are more non-X chromosomes than X-chromosomes, and a recessive fashion because the enzymes from the unaffected genes are generally sufficient to prevent symptoms in carriers.