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Genetic Linkage |
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Certain characteristics may have a tendency to be coinherited; that is they are often transmitted together. Gregor Mendel, in the 19th century, concluded that all characteristics were inherited independently of all others, but it emerged early in the 20th century that this was not always the case. As the structural nature of genes became understood, the mechanism for this phenomenon became clear. Genes are arranged in a linear fashion along chain-like DNA molecules, which are coiled within chromosomes. Genes that are positioned close to one another within a chromosome are less likely to be separated when the chromosomes pair and recombine by crossing over, a process in which fragments of DNA are exchanged between paired chromosomes during the production of gametes. Sex linkage occurs when genetic determinants are found on sex chromosomes—diseases which only manifest themselves in one sex (such as haemophilia) may be sex-linked. RB
See also meiosis.Further reading Bruce Alberts, Molecular Biology of the Cell. |
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