Cytogenetics is the study of the structure of normal and abnormal chromosomes, including examination of chromosome numbers and structure, learning and describing the relationships between chromosome structure and phenotype, and seeking out the causes of chromosomal abnormalities
Chromosomes are visible at metaphase of mitosis. It contains two arms and a centromere. The ends of chromosome arms are called telomeres. According to the position of centromere, chromosomes are classified into 4 types: metacentric (centromere is in the middle), submetacentric (centromere is close to one side), acrocentric (centromere is close to one end) and telocentric (centromere is at one end).
Techniques used in cytogenetics
Three techniques are often used: chromosome banding, karyotyping and FISH. Certain dyes produce reproducible patterns of bands when used to stain chromosomes. Depends on the method and dye, it is classified into three types: Q band, C band and G band. Karyotyping is a standardized arrangement of all the chromosomes of a cell. FISH means Fluorescent in situ Hybridization, Using fluorescence-labeled probes to hybridize to cellular DNA for chromosome visualization.
Variation in chromosome Number
Chromosomal mutations are variations from the wild-type condition in either chromosome structure or chromosome number. Variation in chromosome number includes aneuploidy (changes in one or a few chromosomes) and polyploidy (changes in whole set of chromosomes). Aneuploidy is most common in humans and cause severe genetic diseases.
Variation in chromosome structure
Variation in chromosome structure includes deletion, duplication, inversion, and translocation. These mutations in chromosome structure are caused by unequal crossover and/or abnormal segregation of chromosomes during mitosis. Unbalanced chromosome rearrangement has loss or gain of genetic material, which may causes phenotype or diseases. Balanced chromosome rearrangement may also cause mutations through changes in gene expression.