Raphaël, age 8: “What are chromosomes for?”
Our body is made up of a collection of cells. Inside each cell is a small “sac” called the cell nucleus. It contains the chromosomes, which are the physical carriers of our genetic information.
Giacomo Cavalli, University of Montpellier and Frédéric Bantignies, University of Montpellier
This information is encoded in the deoxyribonucleic acid (DNA) molecule. The entire set of genetic material carried by the chromosomes constitutes the “genome,” which is specific to each living species.
Genes are found within chromosomes; they are small segments of chromosomes, each carrying the information necessary for the synthesis of a protein, which is essential to the structure and functions of cells.
Initially, parents pass on their chromosomes to their children during fertilization, when the sex cells unite. In humans, the very first egg cell contains a total of 46 chromosomes. They function in pairs, with 23 chromosomes from the mother and 23 from the father. We thus inherit the “genetic makeup” of both our parents in its entirety and equally.
Throughout our lives, our cells divide to multiply, which is what allows us to grow and stay healthy. Chromosomes thus enable the entire genetic information to be maintained, replicated, and passed on from cell to cell during an individual’s development and throughout their life.
In humans, the 46 chromosomes contain about 2 meters of DNA. If we were to line up all the DNA from the cells of an adult organism end to end, it would stretch about 500 times the distance between Earth and the Sun!
The human genome contains approximately 23,000 genes, which account for only a very small portion of its total length. The rest of the genome consists of vast regions located around the genes that serve to regulate them, as well as to isolate the genes from neighboring regions so that each gene can be regulated independently. In fact, not all genes can be activated at the same time in all of our cells. This is what allows the cells in your heart to be different from those in your skin, for example.
Giacomo Cavalli, CNRS Research Director, University of Montpellier and Frédéric Bantignies, CNRS Researcher, University of Montpellier
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