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Unlock This CourseHave you ever wondered why no two people look exactly the same (except identical twins)? Or why plants of the same species can look quite different? The answer lies in variation - the differences we see between individuals of the same species. Understanding where this variation comes from is crucial for understanding inheritance, evolution and how life adapts to changing environments.
Variation exists everywhere in nature. From the different colours of flowers in a field to the varying heights of students in your class, these differences make each organism unique. But what causes this variation?
Key Definitions:
All variation in living organisms comes from just two main sources: genetic factors (what you inherit from your parents) and environmental factors (what happens to you during your life). Most characteristics are actually influenced by both!
Genetic variation is the foundation of inheritance. It's the reason why children look similar to their parents but not identical (unless they're identical twins). This type of variation is passed down through genes and is present from the moment of conception.
Genetic variation comes about through several key processes during sexual reproduction. Each of these processes shuffles genes like a deck of cards, creating new combinations that make each individual unique.
During meiosis, chromosomes line up randomly. This means genes on different chromosomes are mixed independently, creating millions of possible combinations in gametes.
Chromosomes swap sections during meiosis, creating new combinations of genes that weren't present in either parent. This process happens in every meiosis.
Any sperm can fertilise any egg and since each gamete is genetically unique, this creates even more variation in offspring.
Humans have 23 pairs of chromosomes. Due to independent assortment alone, each person can produce over 8 million different types of gametes! When you combine this with crossing over and random fertilisation, the number of possible genetic combinations becomes astronomical - which is why each person (except identical twins) is genetically unique.
Some characteristics are controlled entirely by genes and show little or no environmental influence. These include:
Environmental variation occurs when the environment affects how an organism develops or appears. This type of variation is not inherited - it develops during an organism's lifetime based on the conditions it experiences.
Many different environmental factors can influence how organisms develop and what they look like. These factors can work alone or together to create variation.
Temperature, sunlight and rainfall affect growth. Arctic foxes grow thicker fur in winter and plants grow differently in various climates.
Diet affects growth and development. Well-fed animals grow larger, while poor nutrition can stunt growth and affect health.
Physical activity builds muscle mass and affects body shape. Athletes develop different body types based on their training.
Many characteristics show pure environmental variation, meaning they're not inherited at all:
Hydrangea flowers provide a perfect example of environmental variation. The same plant can produce pink flowers in alkaline soil and blue flowers in acidic soil. The genes for flower production are identical, but the soil pH changes how the genes are expressed. Gardeners can actually change the flower colour by adjusting soil acidity!
Most characteristics aren't purely genetic or purely environmental - they're influenced by both factors working together. This interaction creates the complex patterns of variation we see in nature.
Human height perfectly demonstrates how genetic and environmental factors interact. Your genes set your potential maximum height, but environmental factors determine whether you reach that potential.
Multiple genes influence height potential. Tall parents tend to have tall children because they pass on 'tall' gene variants. However, genes only set the range of possible heights.
Nutrition, especially during childhood, greatly affects final height. Disease, stress and living conditions also play important roles in determining actual height achieved.
Variation can be classified into two main types based on how the differences appear in populations.
Shows a smooth range of values with no distinct categories. Examples include height, weight and skin colour. Usually controlled by multiple genes and influenced by environment. Creates a bell-shaped curve when graphed.
Shows distinct categories with no intermediates. Examples include blood groups, sex and tongue rolling ability. Usually controlled by single genes with little environmental influence. Creates bar charts when graphed.
Charles Darwin studied finches on the Galápagos Islands and noticed variation in beak shapes. This variation had both genetic and environmental components. Different islands had different food sources and over many generations, finches with beaks best suited to available food survived better and reproduced more. This led to genetic changes in beak shape - a perfect example of how environmental pressures can influence genetic variation over time.
Variation isn't just interesting - it's essential for life on Earth. Without variation, species couldn't adapt to changing environments or evolve new characteristics.
Understanding sources of variation helps us appreciate the complexity of inheritance and the importance of both our genes and our environment in making us who we are. It also helps explain why biodiversity is so important for the survival of species and ecosystems.