The eukaryotic chromosomes are detected to occur during cell division and are in their most condensed form during metaphase when the sister chromatids are attached. This is the primary stage when cytogenetic analysis is performed. The eukaryotic species possess at least one pair of chromosomes. Most have more than one pair. Each species is characterized by a karyotype. The karyotype is a description of the number of chromosomes in the normal diploid cell, as well as their size distribution. For example, the human chromosome complement has 23 pairs of chromosomes, 22 somatic pairs and one pair of sex chromosomes. One important aspect of genetic research is correlating changes in the karyotype with changes in (he phenotype of the individual.
To further distinguish among chromosomes, they are treated with a dye that stains the DNAin a reproducible manner. After staining, some of the regions are lightly stained and others are heavily stained. As described above, the lightly stained regions are called euchromatin, and the dark stained region is called heterochromatin. The current dye of choice is the Giemsa stain, and the resulting pattern is called the G-banding pattern.
Karyotype of human chromosome-Male
Karyotype of human chromosome-Female