Chromosomes

Human cells are diploid, contain double set of chromosomes. 23 chromosomes (n) – genome – already contain complete information. Pairs having the same genes are called homologous. They look similar, have the same shape and length.

Before the cell division duplication of genetic material (DNA replication) takes place. Chromosomes become visible during division as two copies join in the centromer. What is called chromosome is single DNA particle (n) as well as doubled sister chromatids (2n). Centromer which is narrowness of chromosome can be situated in different places. It is certain for each chromosome.

After coloring, every chromosome receive a characteristic pattern of dark and light stripes. Homologous chromosomes can be identified by that pattern.

Homologous chromosomes can have different versions of the gene - alleles. Persons that have different alleles are called heterozygotes. Both alleles are the same for homozygotes.