In part one of this series, we looked at basic genetics concepts such as DNA, inheritance, and cells and cell division, and in part two we examined more difficult ideas, such as dominance and recessivity, sex-linked traits, genetic pathways, development and environmental effects. From here on, I'm going to assume you're comfortable with all of this, so please review if necessary.
So far, we've just considered situations where everything goes to plan, focussing mostly on theoretical concepts. But real life is messy, so let's conclude this series by switching our attention to some practical applications of genetics, by taking a brief look at chromosome variations, genetic mutation, cancer, selective breeding and disease genetics.
This is the second article in a three-part series on genetics. In part one, we began with some basic concepts: looking at cells, the structure and replication of DNA, genes and what they do, and how cell division and genetic inheritance work. This article will delve a little deeper into some slightly more challenging concepts.
Let's go back to the genes. We have two copies of each gene, one from each parent. But what if these copies are different from one another? How does this change things? In fact, this is often the case. Most genes come in several different forms, called alleles. If genes were cars, then alleles could be Honda, Tesla or Lamborghini. Although affecting the same trait or traits, different alleles have differing DNA sequences, resulting in variations in the proteins they produce. Each of our 20,000 genes is located in a specific position (called a locus) on one of our chromosomes. All the alleles for a given gene can thus be found in the same position on the same chromosome as one another, but there can only be one of the possible alleles on any particular chromosome.
Why do some traits appear in grandparents and grandchildren, skipping the intervening generation? Are there really genes for intelligence, running, mental arithmetic? More broadly, are we in any sense controlled by our genes? How far has our understanding of genetics advanced in recent years, and where is the field heading? What about ethical issues raised by new genetic technologies?
A conceptual understanding of genetics is mandatory for anyone wishing to truly understand questions like these. And, if we don't want to be misled by grandiose or unfounded claims that are regularly made about genetics, we need a solid grasp of how genetics works. This is today more vital than ever, given the ever-accelerating pace of research.
This is the first of a three-part series that collectively aims to cover all the major concepts required for a solid understanding of modern genetics. This article will give you a tour of the basics, with no prior knowledge required. In part two I'll expand on this foundation by covering more complex concepts, and part three will conclude the series by discussing some human-specific areas of genetics in greater detail.
After reading this series, you should have a much more sophisticated understanding of genetics, and you'll be able to utilize this as I plan to write more specialized articles on diseases and other genetics-related stories in the news, several of which will be critiques of a few of the many dubious claims propagated by the media.
Let's start the discussion with three somewhat familiar concepts: cells, genes and DNA.