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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Genetic vs Environmental Variation
Variation is all about differences between individuals of the same species. Look around your classroom - everyone looks different! These differences are what biologists call variation and understanding where they come from is key to understanding evolution.
Key Definitions:
Genetic variation comes from differences in our DNA. These differences are inherited from our parents and can't be changed by the environment. Eye colour, blood group and ear lobe shape are all examples of genetic variation in humans.
Environmental variation is caused by external factors like diet, climate, or lifestyle. These differences aren't inherited but develop during an individual's lifetime. Examples include language, scars and muscle development through exercise.
Variation can be classified in different ways. One important distinction is between continuous and discontinuous variation.
Characteristics showing continuous variation have a wide range of values with no distinct categories. If you measured the height of everyone in your school, you'd get a smooth range of values from shortest to tallest. Other examples include weight, shoe size and reaction time.
Continuous variation is usually influenced by both genetic and environmental factors.
Characteristics showing discontinuous variation fall into distinct categories with no intermediates. Blood groups (A, B, AB, O) are either one type or another - there's no "half A, half B" blood group. Other examples include tongue rolling ability and ear lobe attachment.
Discontinuous variation is usually controlled by a single gene or a few genes with little environmental influence.
Scientists collect data on variation and display it using graphs. The type of graph depends on the type of variation being studied.
Continuous variation is typically shown using a histogram or frequency curve. When plotted, data often forms a bell-shaped curve called a normal distribution. Most individuals cluster around the average value, with fewer individuals at the extremes.
Discontinuous variation is best displayed using a bar chart, where each bar represents a distinct category. The height of each bar shows how many individuals fall into that category.
Most characteristics are influenced by both genetic and environmental factors, but to different degrees. Understanding this interplay helps us make sense of the variation we see in the world.
Some traits are almost entirely determined by genes, with minimal environmental influence:
Many traits are influenced by both genes and environment:
Some characteristics are primarily determined by environment:
Identical twins develop from a single fertilised egg that splits into two, meaning they have identical DNA. Any differences between identical twins must be due to environmental factors. Studies of identical twins raised apart have helped scientists understand which traits are influenced by genes and which by environment.
For example, identical twins usually have very similar heights (genetic), but may have different weights if they follow different diets (environmental). They might have the same natural hair colour (genetic) but different hairstyles (environmental choice).
Himalayan rabbits have a fascinating coat pattern that demonstrates the interaction between genes and environment. These rabbits have a gene for producing dark fur pigment, but the gene only works at cooler temperatures.
As a result, Himalayan rabbits have white fur over most of their body (where it's warm) but black fur on their extremities like ears, nose and feet (where it's cooler). If you were to warm up a patch of their black fur, the new fur would grow in white!
Variation is essential for evolution by natural selection. Without variation, there would be no differences for natural selection to act upon.
Genetic variation provides the raw material for evolution. When the environment changes, individuals with certain genetic traits may have an advantage, making them more likely to survive and reproduce. Over many generations, this can lead to changes in the species.
Mutations: Random changes in DNA that create new alleles (versions of genes). Most mutations have no effect or are harmful, but occasionally they provide an advantage.
Sexual reproduction: Combines genetic material from two parents, creating unique combinations of genes in offspring.
Scientists can measure genetic variation within a population by studying:
Greater genetic variation generally means a population is more likely to survive environmental changes.
Here are some ways you can investigate variation in your classroom or at home:
Collect data on height, hand span, or reaction time from your class. Create a histogram and see if it forms a normal distribution. Calculate the mean, median and range of your data.
Survey your class for traits like ability to roll tongue, attached/detached earlobes, or whether people can taste PTC paper (a genetic trait). Create a bar chart showing the frequency of each category.
Understanding the difference between genetic and environmental variation is crucial for making sense of the diversity we see in living things. While genetic variation provides the foundation for evolution, environmental variation allows organisms to adapt within their lifetimes.
In your exams, you might be asked to:
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