In 2016, researchers at the University of Liverpool identified the mutation event that gave rise to industrial melanism. Ultimately, this event resulted from the insertion of a large tandemly repeated transposable element into the first intron of the gene cortex.
Statistical inference places this event as occurring around 1819, making it consistent with the timeline for industrial melanism. These findings fill an important gap in the study of microevolutionary change, evolutionary change over a small period of time.1
The case of the peppered moths is just one example of the use of modern genetic technologies for helping understand past events and build upon existing scientific information. Understanding the basics of genetics is important for understanding the biological basis of humans today, as genes explain the basis of heritable traits and diseases.
The gene is the basic unit of heredity. Genes are made up of deoxyribonucleic acids (DNA)—the hereditary material in humans and most other organisms—and serve as instructions to make proteins. In the human genome, genes can range in size from about 100 DNA bases to 2 million bases. The human genome is estimated to have between 20,000 and 25,000 genes.2
Each individual has two copies of each gene, one inherited from each parent, and most genes are the same in all individuals. However, a small number of genes—less than one percent—are different among individuals. These small differences result in unique physical features.
Genes are found on chromosomes, tightly-packed thread-like structures in the cell nucleus made up of DNA coiled around proteins called histones, which support the structure of the chromosome. All chromosomes have indents called centromeres, which divide the chromosomes into two sections. It is the location of the centromere on the chromosome that gives chromosomes their shapes and can be used to describe locations of genes.3
In humans, each cell has 23 pairs of chromosomes or 46 total. Twenty-two of these are autosomes, which are the same in both males and females, while the twenty-third pair is sex chromosomes. These differ between males and females and will either by XY or XX, respectively.4
Only one percent of DNA is actually made up of protein-coding genes, while the other ninety-nine percent is non-coding DNA. However, this DNA is not necessarily useless and may have important functions in controlling gene activity.5
However, even with this complex, highly-regulated system, there is room for error. A gene mutation is a random, permanent change in a DNA sequence making it differ from the sequence found in most individuals. Mutations come in different sizes and can affect only a single base pair or a large region of the chromosome. There are two primary types of mutations: hereditary and acquired mutations.
Hereditary mutations are passed down from parent to offspring through the sperm or egg cells and exist throughout an individual’s life in most of the cells in their body.
Acquired mutations arise at some point during an individual’s life and are present in some, but not all of the body’s cells. These mutations come about as a result of environmental factors like ultraviolet radiation or an error in cell division.
Disease-causing mutations are fairly uncommon in the general population. Other genetic changes like polymorphisms occur in greater than one percent of the population. This makes them common enough to be considered a normal DNA variation. Polymorphisms are what result in differences in eye color, hair color, and blood type.6
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