Introduction to Terminology Used in Genetics
A Look at Inherited Characters, Genes, DNA, Chromosomes & Proteins
Nov 1, 2008
Genetics is about traits or characters, features of individuals that are passed on to offspring (and their offspring, and so on). A person comparing photos of their biological family will likely see resemblances, such as the recurrence of a nose shape or hair colour. Differences in relatives are also likely to be noticeable. When a character is passed on, it is inherited.
What are Genes?
Genes are units that measure inheritance. They are responsible for characters, both visible (such as eye colour) and invisible (such as fat type). Alongside environmental factors, genes also play a strong role in behavior and health. Someone may be prone to heart disease (genes), but can reduce their risk through lifestyle choices (environment).
Where are the Genes Stored?
Physically, genes are pieces of a molecule called DNA, which is packed into chromosomes, which reside in cell nuclei *, which are within cells. This definition can be broken down:
- Cells are basic, functioning units of an organism (life form). For example, in humans, the function of red blood cells is to deliver oxygen to the body’s tissues. Most human cells are invisible to the naked eye.
- These cells contain important functioning structures (organelles) called nuclei.
- Chromosomes are linear-shaped structures protected within the nuclei. They are made up of proteins and DNA.
- DNA (deoxyribonucleic acid) is a molecule containing genetic instructions – the genes. These instructions tell the cell what to do.
(* Some cells, such as the single-cellular organism bacteria, do not have nuclei. Their cells do contain genetic material, which floats loosely inside the cell’s fluid.)
DNA and Chromosomes in More Detail
DNA molecules have a double helix shape (sometimes compared to a “twisted ladder”). It is composed of four chemicals, each represented by their initial letters:
- Adenine (A)
- Cytosine (C)
- Guanine (G)
- Thymine (T)
These chemicals make a quaternary code. Just as binary uses 1s and 0s, genetic code uses the letters A, C, G and T. These chemicals, or letters, work in a specific order:
- A pairs with T
- C pairs with G
The University of Utah’s Genetic Science Learning Center website compares the DNA letters to an alphabet. In English, a sentence is a meaningful collection of words. The DNA letters can be looked upon in a similar way, where a gene is a meaningful collection of these DNA letters (chemicals).
Why is DNA packaged into chromosomes? There is a lot of DNA in one cell, and chromosomes allow this DNA to be condensed (tightly coiled around proteins) for safe storage. The number of chromosomes per cell depends on the organism. For example, humans have 46 chromosomes, whereas as onions have 16.
What are Proteins?
Genes instruct proteins, which in turn tell cells what to do. Hemoglobin, for example, is the protein that tells red blood cells to locate and transport oxygen to the body’s tissues. If the human body was a machine, the proteins could be called cogs, each with different functions that make the body survive and grow.
For a closer look at cell biology, including eukaryotic and prokaryotic cells, read Basic Cell Biology for Understanding Genetics. Read Useful Science Basics for Understanding Genetics for a look at other science principles involved in learning about genes.
Sources
Inheritance of Characters (SK195_1), The Open University (OpenLearn – Learning Space) website, accessed 30th October 2008, no authors specified.
The cells, tissue and organisations of the body, Anatomy and Physiology (9th edition), published by Ross and Wilson in 2001, authors Anne Waugh and Alison Grant.
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