All the genes on a chromosome are said to be linked to one another and belong to the same linkage group. The phenomenon of inheritance of linked genes in same linkage group is called linkage.
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Linkage
An organism often has many phenotypic traits in its body. Because, each phenotypic trait of an organism is determined by at least, a pair of alleles (genes) which reside at specific gene loci of homologous chromosomes (autosomes or sex chromosomes), therefore, it can be expected that an organism may has numerous genes for its various phenotypic traits. The number of genes of an organism thus, may exceed the number of its chromosomes, because, commonly most organisms contain limited number of chromosomes. For instance man has thousands of pairs of genes, but only 23 pairs of chromosomes. Hence each chromosome must contain a large numbers of genes. Further, because the chromosomes are inherited as units; that is, they pair and segregate in meiosis as units to gametes, so, all of the genes which may specify various different phenotypic traits but are located in any given chromosomes, tend to be inherited together.
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