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Inheritance of genetic conditions

A person can be affected by a genetic condition if he or she inherits a particular changed version of a gene. Sometimes the gene can be missing altogether. Different versions of the same gene are called alleles. A genetic condition can be dominant - when the effects of a faulty allele mask those of a working one; or recessive - when the effects of a working allele mask those of a faulty one. A condition may also show X-linked inheritance.

Genes are made of DNA.
Mark Pallen, Queen's University Belfast

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