Each chromosome carries a number of genes on it. Genes are linearly arranged at specific position on chromosomes. The position of a gene on the chromosome is called its locus. It is its home. The linear order of the gene loci on one homologue corresponds to that of its partner homologue. Karyotype is the entire chromosome complement of an individual or cell. While genome is the total amount of genetic material in a chromosome set of an individual.
All the genes present on a chromosome are linked to each other. This phenomenon of staying together of all the genes of a chromosome is called linkage. Wherever a chromosome moves, it carries its riding genes en bloc in the form of a linkage group.
“The number of linkage groups corresponds to the number of homologous pairs of chromosomes. You have 23 linkage groups. How many does a frog have?”
17.2.1 Alleles Their Origin and Iimpact
Like chromosomes, genes also form pairs. Partners of a gene pair are called alleles. Each allele of a gene pair occupies the same gene locus on its respective homologue. The partner genes or alleles may be identical to each other; i.e., each other’s true copies, or slightly different from each other, altered copies. These altered, alternative forms of a gene arise by a sudden change in the structure of a gene. This change is called gene mutation (fig 17.1).
Gene A ……….mutation a
Gene B………..mutation b
