Chromosome 101

Scientists estimate that on average, a human being has 37.2 trillion cells. In every cell, there is a nucleus (except for red blood cells) which contains identical sets of chromosomes found in pairs. Pairs of human chromosomes are numbered from 1 through 22, with an unequal 23rd pair of X and Y chromosomes for males and two X chromosomes for females. Chromosomes carry the genetic characteristics of each individual, collectively called the human genome. Each chromosome is a flexible structure made of material called DNA, which is one long molecule that appear like tightly coiled strands. The coding order of the DNA makes up genes, which are a segment of a chromosome. In other words, genes contain the code for making proteins, the building blocks of life.

Chromosomes are the structures that hold genes. Scientists are working to decipher what every gene on the human genome does, but they still have a lot to learn. This unique genotype is a complete set instructions that help the body synthesize proteins. The genotype dictates how the body is supposed to be built and function. This results in specific and unique physical and medical characteristics for every human being.

The Human Genome Project has revealed that there are probably about 20,000-25,000 ‘haploid’ protein coding genes. Chromosome 8 contains around 4.5 to 5 percent of the total DNA in cells, which is probably around 700 genes up to 1400 genes. Chromosome 8 contains about 146 million base pairs or DNA building blocks, of which over 95% have been determined.

Each chromosome has a short arm designated as “p,” a long arm identified by the letter “q,” and a narrowed region at which the two arms are joined (centromere). Chromosomes are further subdivided into bands that are numbered outward from the centromere. Telomeres are cells at the ends of the chromosomes which protect it.

During cell division, or mitosis, a parent cell divides into two or more daughter cells. Each new cell gets a complete copy of all the DNA from the parent cell (all 46 chromosomes). Cell division regulated itself depending on needs for growth and repair, and do so at different rates for different types of cells. Nerve and brain cells divide much less often than skin cells, for example.

In genetics screening, a karyotype is an actual photograph of the chromosomes from one cell. The cells analyzed are usually white blood cells. Cytogenetics is a word for the study of chromosomes.