If you wiki the terms Gene, Genome and Chromosome you’ll be in a world of confusion as neither definition is succinct nor static. Making sense of basic genetics revolves around understanding these terms as they permeate every aspect of genetics from the morosely academic to the basic ancestry DNA test.
If you don’t have a basic grasp of the terms gene, genome, and chromosome, understanding alleles, base pairs, STRs, and SNPs will be out of the question. In fact, just staring at the growing range of DNA testing sites available who promise you very flashy results, you will be ill-prepared to decipher what they are actually offering you. Let’s get to it, shall we!
In basic metaphoric parlance, a GENOME is a BOOK, and a CHROMOSOME is a CHAPTER. GENES are bold-faced passages that highlight HEREDITARY INFORMATION.
GENOME = (A book) The entire sequence of human DNA, over 3 billion strands.
CHROMOSOME = (A Chapter) Sections of DNA within the human genome, 23 pairs.*
GENE = (Passages) Sections of DNA that encode hereditary functions. There are only about 20,000 genes on any given human genome, about 1.5% of its total length.
*Technically the term “23 pairs” is a misnomer because, while every person has 22 pairs of autosomes, not all people have a “pair” of allosomes, or gender chromosomes (the X and Y). It’s kind of nit-picky but what adds to the general frustration of learning the science of genetics in general. Only females have “23 pairs” as they have two X chromosomes (allosomes), and men do not as we have an X and a Y – last time I checked, that’s not a pair!
Each CHROMOSOME is made up of 23 sections: 22 autosomes, and 1 allosome. ALLOSOMES are ‘sex’ genes and determine our gender, both reside in the cell nucleus. The male Y chromosome is very small by comparison and is only passed down from father to son. The female X chromosome is super huge and very special, it’s the second largest of all of our human chromosomes!
Be aware, the female X chromosome is NOT the same as mtDNA. Mitochondrial DNA, or mtDNA, is only passed from mother to daughter and does not reside in the cell nucleus along with the “23 pairs” of chromosomes. Mitochondrial DNA, as its name implies, resides in the cell’s mitochondria, or power plant. Mitochondria are found within all body cells and are located within a cell’s cytoplasm.
AUTOSOMES are the bulk of our chromosomes, and by implication, our genome. Autosomes are made up of mostly non-coding DNA and a very small portion of coded DNA that we call GENES. Genes are the hereditary part of our DNA, in very basic terms.
97% of our DNA is carried in our 22 autosomes and our X chromosome! Sorry Ys guys. Our human genome is huge! It’s over 3 billion base pairs long and excruciatingly complex, so much so that the science of genetics is constantly in flux over what constitutes what.
Sufficed to say though that our human genome is a very beautifully-bound book with 23 chapters in it. Randomly appearing in each of those chapters are highlighted passages, bold-faced sections that are the most important part to the average person looking for hereditary information. Those highlighted sentences, just like when we read, jump out at us and summarize what we’ve been reading. Those sections are our genes, the encoded sections that tell us who we are and where we come from.
This article is a very basic introduction to human genetics, just enough to get one off the ground, so to speak, and be able to tackle larger and more complex definitions and concepts. A world-renown geneticist might read this and chuckle; however, we all have to start somewhere in our journey to understand our DNA and where our ancestry came from. To understand basic genetics, the terms GENE, GENOME and CHROMOSOME must be able to be used in basic conversation and it is why I have distilled them down to use in your research, both as individual definitions and related concepts.