LECTURE NOTES ON LINKAGE GROUPS

LINKAGE GROUPS

All the linked genes of a chromosome form a linkage group. Because, all the genes of a chromosome have their identical genes (alleomorphs) on the homologous chromosome, therefore linkage groups of a homologous pair of chromosome is considered as one. The number of linkage group of a species, thus, corresponds with haploid chromosome number of that species.

Example.

 1. Drosophila has 4 pairs of chromosomes and 4 linkage groups.

2. Man has 23 pairs of chromosomes and 23 linkage groups.

3. Corn (Zea mays) has 10 pairs of chromosomes and 10 linkage groups.

However, in organisms the female or male sex having dissimilar sex chromosomes (e.g., human beings, Drosophila, fowl, etc.), one more linkage group occur than the haploid number .

Example.

1. Female human beings = 22 pairs of autosomes or non-sex chromosomes + 1 pair of

: homomorphic X chromosomes= 22 autosomal linkage groups + 1 X chromosomal linkage group = 23 linkage groups.

2. Male human beings : = 22 pairs of autosomes + 2 heteromorphic sex chromosomes, i.e., 1 X chromosome + 1 Y chromosome= 22 autosomal linkage group + 1 X chromosomal linkage group + 1 Y chromosomal linkage group= 24 linkage groups.