Genes contain instructions for a wide variety of proteins, which make up the machinery of your cells and body. They ultimately help an embryo develop, and keep your body functioning properly. These genes are contained in chromosomes, which you inherit from your parents.
It might be helpful to think of chromosomes like sets of books your parents gave you. Imagine that you got a set of 23 books from one parent, and a set of 23 books from the other parent. This is one way to think about your inherited pairs of chromosomes. When you look at the titles of these books, they are the exact same: you end up with two copies of the same 23 books. Furthermore, imagine each set of books went through different editors. Even though the two books are basically the same, there may be slight differences inside. The same is true for chromosomes: even though the sets of chromosomes are largely the same, there are some differences depending on which parent they came from.
When scientists study chromosomes, they number each pair of chromosomes from largest to smallest. Most people have 23 pairs of chromosomes, 46 total. Every cell in your body has the same 23 pairs of chromosomes. These chromosomes contain the instructions needed to make all of your proteins, which help your cells, tissues, and organs develop and function properly. Each cell decides which protein instructions to follow, and which to ignore, depending on what that cell’s job is.
To give an example, the BRCA1 gene is located on chromosome 17, while BRCA2 is located on chromosome 13. For our purpose, let us focus on BRCA-2.
Everybody has two BRCA2 genes, one from each parent. You can compare these to the same chapter in the pair of books you inherited. The two genes are almost identical, but may contain small differences from each other. Not only does the gene you get from one parent differ from the other parent, but your two genes might also differ from the rest of the population. When compared to other people, your gene might be spelled differently. This different spelling is due to a variant, which is a specific change at a specific location in your DNA. It makes your gene spelled slightly differently than most other peoples’. Scientists can observe these spellings through methods of genome sequencing**. **
