Chromosomes

The chromosomes are thread like structures present in the nucleus of an eukaryotic cells . They are DNA molecule compacted with proteins .Chromosomes vary widely between different organisms. Each species has a characteristic number of chromosomes. Eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have smaller circular chromosomes. There are many exceptions to this rule. Mitochondria in most eukaryotes and chloroplasts in plants have their own small chromosomes.

Humans have 23 pairs of chromosomes , of which 22 pairs are autosomes or body chromosomes  . Autosomes  look the same in both males and females . Apart from autosomes there is a  pair of  allosome or sex chromosomes which differ between males and females.

Each pair contains two chromosomes, one acquired from each parent, which means that children inherit half of their chromosomes from their mother and half from their father. Chromosomes can be seen through a microscope when the nucleus dissolves during cell division.

The matched pairs of chromosomes in a diploid organism are called homologous chromosomes. Homologous chromosomes are of  the same length and have genes in exactly the same location, or locus.A somatic cell contains two matched sets of chromosomes, a configuration known as diploid ( 2n)  where ‘ n’ represent a single set of chromosomes;

Gametes, or sex cells  (eggs and sperm )  contain only one set of 23 chromosomes (n)  and are designated  as haploid.

The variation of individuals within a species is caused by the specific combination of the genes inherited from both parents. Genes are expressed as characteristics of the organism . Each characteristic may have different variants called traits . Traits are caused by differences in the DNA sequence for a gene. An organism’s traits are determined largely by the genes     inherited from each parent and also by the environment that they experience.

“Chromosomes” by Andreas Bolzer, Gregor Kreth, Irina Solovei, Daniela Koehler, Kaan Saracoglu, Christine Fauth, Stefan Müller, Roland Eils, Christoph Cremer, Michael R. Speicher, Thomas Cremer, is licensed under CC BY-SA 2.5