DNA, Genes, & Chromosomes

Introduction

Learning about human genetics can seem to be a daunting task. However, by breaking down the information into smaller pieces, we can make sense of it!

Biological life is built upon four major classes of molecules that exist in all of the cells of your body: carbohydrates, fats, proteins, and nucleic acids. This blog post will provide a basic introduction to DNA (a type of nucleic acid), genes and chromosomes.

What is DNA?

DNA, which is short for deoxyribonucleic acid, is what our bodies use to store genetic information or instructions. These instructions are used to allow our bodies to perform all of our day-to-day functions, like storing energy and breaking down food. DNA is spelled with four different letters, or base pairs: adenine (A), thymine (T), cytosine (C) and guanine (G). Your DNA is billions of letters long, and it would fill up to four thousand 500-page books if it were to be printed out! Changes or differences in how our DNA is spelled are called genetic variants. In some cases, genetic variants may be harmful and increase risk for disease. However, the vast majority of these differences in spelling are harmless and are part of what makes each of us unique.

What are Genes?

Genes refer to sections of DNA that code for specific instructions, such as the instructions to form a protein. The genes in your body vary in size, with some only a few hundred base pairs long and others thousands of base pairs in length [1]. Genes can be regulated, or controlled, by other genes or environmental factors, which allows your body to adapt to a variety of situations.

What are Chromosomes?

How does the cell store all of these genes and DNA? Answer: chromosomes. Chromosomes contain DNA strands tightly coiled around proteins called histones. When the body needs to reference specific genes, the region near their location in the chromosome is temporarily unwound. When a gene is not in use, it returns to the normal tightly-wound configuration for efficient storage. This is how the cell can pack about 6 feet of DNA into a single cell! [2]

The human genome contains 23 pairs of chromosomes. One pair comes from your mother and the other pair comes from your father. Because most chromosomes come in pairs, we each have two copies of most genes. Biological sex is determined by the sex chromosomes (see boxed pairs above – XX for females, XY for males).

Conclusion

This blog post has covered the different levels of organization for your body’s genetic information from simplest to most complex. Human understanding of the genome continues to grow each year as more discoveries are made, and it is an exciting time for medicine. If your provider feels genetic testing may be appropriate for you, but you are unsure of what to expect, see this blog post for more detailed information. If you have further questions, be sure to write them down; a healthcare provider or genetic counselor should be able to answer them!

References

https://bionumbers.hms.harvard.edu/files/Human%20genome%20and%20human%20gene%20statistics.pdf

https://www.sciencefocus.com/the-human-body/how-long-is-your-dna/