Prof. Dr. Sohan Raj Tater
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Our genetic information is stored in 23 pair of chromosomes that vary widely in size and shape. Chromosome 1 is the largest and is over three times bigger than chromosome 22. The 23rd pair of chromosome are two special chromosomes, X and Y, that determine our sex. Females have a pair of X chromosome (46, XX), where as males have one X and one Y chromosomes (46, XY). Chromosomes are made of DNA, and genes are special units of chromosomal DNA. Each chromosome is a very long molecule so it needs to be wrapped tightly around protein for efficient packaging.
Near the centre of each chromosome is its centromere, a narrow region that divides the chromosome into a long arm (q) and a short arm (p). We can further divide the chromosomes using special stains that produce strips known as banding pattern. Each chromosome has a distinct banding pattern, and each band is numbered to help identify a particular region of a chromosome. This method of mapping a gene to a particular band of chromosome is called cytogenetic mapping. For example, the hemoglobin beta gene (HBB) is found on chromosome 11p 15.4. This means that the HBB gene lies on the short aim(p) of chromosome 11 and is found at the band labeled 15.4.
With the advent of new techniques in DNA analysis, we are able to look into chromosome in much greater detail. Where as cytogenetic mapping gives a bird's eye view of the chromosomes. More modern methods show DNA at a much higher resolution. The human Genome project aims to identify of sequence the 30,000 genes in human DNA.
Doctoral Thesis, JVBU