In a given species, chromosomes can be identified by their number, size, centromere position, and banding pattern. In a human karyotype, autosomes or “body chromosomes” (all of the non–sex chromosomes) are generally organized in approximate order of size from largest (chromosome 1) to smallest (chromosome 22).

Chromosomes are structures made of nucleic acids and protein, are found in the nucleus of most living cells, and carry genetic information in the form of genes. They contain all the information used to make the cell grow, thrive, and reproduce (in other words, they make the organism what it is).

Chromosomes are located inside of the nucleus of cells. Each chromosome is one long single molecule of DNA. This DNA contains important genetic information. Chromosomes have a unique structure, which helps to keep the DNA tightly wrapped around the proteins called histones.

Chromosome 1 is the largest human chromosome, spanning about 249 million DNA building blocks (base pairs) and representing approximately 8 percent of the total DNA in cells. Identifying genes on each chromosome is an active area of genetic research.

Chromosome 12 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 12 spans about 133 million base pairs (the building material of DNA) and represents between 4 and 4.5 percent of the total DNA in cells….

Human karyotype The most common karyotypes for females contain two X chromosomes and are denoted 46,XX; males usually have both an X and a Y chromosome denoted 46,XY. Approximately 1.7% percent of humans are intersex, sometimes due to variations in sex chromosomes.

In humans, females inherit an X chromosome from each parent, whereas males always inherit their X chromosome from their mother and their Y chromosome from their father.

Males with XYY syndrome have 47 chromosomes because of the extra Y chromosome. This condition is also sometimes called Jacob’s syndrome, XYY karyotype, or YY syndrome. According to the National Institutes of Health, XYY syndrome occurs in 1 out of every 1,000 boys.

Chromosome 21

SRY (which stands for sex-determining region Y gene) is found on the Y chromosome.

SRY is the HUGO Gene Nomenclature Committee assigned symbol for the mammalian gene “sex determining region Y”. SRY is an abbreviation that can also mean: “Sorry” (see Suffering), as a slang abbreviation for an expression of sympathy for another’s suffering.

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