What are Chromosomes? | Types, Definition, Structure, Function & Facts
What are Chromosomes?
Chromosomes are small structures inside cells made up of DNA and proteins. The information in chromosomes acts as a recipe for cells to know how to function and reproduce. Every life form has its own set of instructions, including you. Your chromosomes help describe the unique traits you’ll develop like eye color and size.
Where are Chromosomes Found?
Chromosomes are found in the nucleus of every cell. Different life forms have different numbers of chromosomes in each cell. Humans have 23 pairs of chromosomes for a total of 46 chromosomes in each cell.
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Can we see them?
Normally we cannot see the chromosomes. They are so small and thin that you cannot see them even with a powerful microscope. However, when a cell prepares to divide, the chromosomes roll up and close together. With a high-powered microscope, scientists can see the chromosomes. They usually come in pairs and look like small, short worms.
What do they look like?
When a cell does not divide (called interphase of the cell cycle), the chromosomes stay in the form of chromosomes. In this form, it is a long and very thin thread. When the cell begins to divide, this filament replicates and turns into shorter tubes. Before separation, the two tubes are clamped together at a point called the centromere. The shorter branches of the tube are called the “p-arm” and the longer ones are called the “q-arm”.
Different info of Chromosomes
Different chromosomes carry different types of information. For example, one chromosome may contain information about eye color and size while another may determine blood type.
Genes
Within each chromosome are specific parts of DNA called genes. Each gene contains the code or recipe for making a particular protein. These proteins determine our development and the traits we inherit from our parents. Genes are sometimes called genetic units.
Allele
When we talk about a gene, we are referring to a piece of DNA. An example of this would be the gene that determines your hair color. When we talk about a particular sequence of a gene (such as the sequence that gives you black hair versus the sequence that gives you blonde hair), it is called an allele. So everyone has a gene that determines their hair color, only blondes have the allele for blonde hair.
Human Chromosomes
As we mentioned above, humans have 23 different chromosome pairs for a total of 46 chromosomes. We all get 23 chromosomes from our mother and 23 from our father. Scientists number these pairs from 1 to 22, and then an additional pair known as the “X/Y” pair. The X/Y pair determines whether you are male or female. Females have two X chromosomes known as XX, while males have one X and one Y chromosome known as XY.
Chromosomes in Different Animals
Different organisms have different numbers of chromosomes: horses have 64, rabbits have 44, and fruit flies have 8.