What makes chromosomes different from each other

What's DNA? What's Genome Sequencing? What's a genome map? What are genome variations? The important word here is "package": chromosomes help a cell to keep a large amount of genetic information neat, organized, and compact. Chromosomes are made of DNA and protein. Most living things have chromosomes that are linear, like bits of fat thread, and are kept in the nucleus, a sphere-shaped sac within the cell. In a few very simple forms of life, such as bacteria, the entire genome is packaged into a single chromosome.

But other organisms, with genomes a thousand or even a million times larger than those of bacteria, divide their hereditary material among a number of different chromosomes. Exactly how many chromosomes we are talking about depends on the species. A mosquito has 6 chromosomes, a pea plant has 14, a sunflower 34, a human being 46, and a dog Closely related species tend to have a similar number of chromosomes.

For example, chimpanzees, our closest cousins, have 48 chromosomes in each of their cells. But aside from this general rule, there is very little rhyme or reason to how many chromosomes a species has. It would be convenient if there were some type of "evolutionary ladder," with more complex organisms having more chromosomes, but nature does not work that way.

Goldfish, which spend their days swimming in circles, lazily blowing bubbles, and hovering near the top of their bowl in anticipation of fish flakes, are provided with 94 chromosomes. Cats, with their keen hunting techniques and thousand ways to purringly manipulate human beings, have only Though similar in basic appearance, different chromosomes vary slightly in size and shape. Chromosomes are bundles of tightly coiled DNA located within the nucleus of almost every cell in our body.

Humans have 23 pairs of chromosomes. Illustration showing how DNA is packaged into a chromosome. Image credit: Genome Research Limited. Cells are the basic building blocks of living things. The human body is composed of trillions of cells, all with their own specialised function. DNA or deoxyribonucleic acid is a long molecule that contains our unique genetic code.

Like a recipe book it holds the instructions for making all the proteins in our bodies. Telomeres are distinctive structures found at the ends of our chromosomes. They consist of the same short DNA sequence repeated over and over again. Inheritance is the process by which genetic information is passed on from parent to child. When two reproductive cells unite, they become a single cell that contains two copies of each chromosome.

This cell then divides and its successors divide numerous times, eventually producing a mature individual with a full set of paired chromosomes in virtually all of its cells. Besides the linear chromosomes found in the nucleus, the cells of humans and other complex organisms carry a much smaller type of chromosome similar to those seen in bacteria.

This circular chromosome is found in mitochondria, which are structures located outside the nucleus that serve as the cell's powerhouses. Scientists think that, in the past, mitochondria were free-living bacteria with the ability to convert oxygen into energy. When these bacteria invaded cells lacking the power to tap into oxygen's power, the cells retained them, and, over time, the bacteria evolved into modern-day mitochondria. The constricted region of linear chromosomes is known as the centromere.

Although this constriction is called the centromere, it usually is not located exactly in the center of the chromosome and, in some cases, is located almost at the chromosome's end. The regions on either side of the centromere are referred to as the chromosome's arms. Centromeres help to keep chromosomes properly aligned during the complex process of cell division. As chromosomes are copied in preparation for production of a new cell, the centromere serves as an attachment site for the two halves of each replicated chromosome, known as sister chromatids.

Telomeres are repetitive stretches of DNA located at the ends of linear chromosomes. They protect the ends of chromosomes in a manner similar to the way the tips of shoelaces keep them from unraveling. In many types of cells, telomeres lose a bit of their DNA every time a cell divides.

Eventually, when all of the telomere DNA is gone, the cell cannot replicate and dies. White blood cells and other cell types with the capacity to divide very frequently have a special enzyme that prevents their chromosomes from losing their telomeres. Because they retain their telomeres, such cells generally live longer than other cells.

Telomeres also play a role in cancer. The chromosomes of malignant cells usually do not lose their telomeres, helping to fuel the uncontrolled growth that makes cancer so devastating. In fact, each species of plants and animals has a set number of chromosomes. A fruit fly, for example, has four pairs of chromosomes, while a rice plant has 12 and a dog, In humans and most other complex organisms, one copy of each chromosome is inherited from the female parent and the other from the male parent.

This explains why children inherit some of their traits from their mother and others from their father. The pattern of inheritance is different for the small circular chromosome found in mitochondria.