DNA and histone proteins are packaged into structures called chromosomes.
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences.
Chromosomes also contain DNA–bound proteins, which serve to package the DNA and control its functions. Chromosomal DNA encodes most or all of an organism's genetic information; some species also contain plasmids or other extrachromosomal genetic elements.
In unisexual organisms, the chromosomes can be distinguished into autosomes and allosomes. Autosomes or somatic chromosomes carry genes which determine the somatic characteristics and do not have any influence on determining the sex of the organism. Allosomes are sex chromosomes which carry genes responsible for sexual characteristics and as such have a significant role in the determination of sex.
Each cell contains 23 pairs of chromosomes a total of 46 chromosomes. The first 22 pairs are called autosomes which look exactly the same in both males and females. The 23rd pair of chromosomes is called an allosome. These sex chromosomes differ between males and females. Females have two copies of the X chromosome, while males have one X chromosome and one Y chromosome. The X chromosome is present in the ovum, while either X or Y chromosomes can be present in sperm.
During fertilization, Half of our allosomes are transferred from maternal and half from paternal origin. For someone to be considered a female, one must receive an X chromosome from both parents, whereas to be considered a male, one must receive a X chromosome from their mother and a Y chromosome from their father. It is thus the males sperm that determines the gender of each offspring in humans. There is a 50 percent chance of reproducing a male or a female.
Karyotype – An organized profile of a person's chromosomes
A karyotype is an organized profile of a person's chromosomes. In a karyotype, chromosomes are arranged and numbered by size, from largest to smallest. This arrangement helps scientists quickly identify chromosomal alterations that may result in a genetic disorder. To make a karyotype, scientists take a picture of someone's chromosomes, cut them out and match them up using size, banding pattern and centromere position as guides.