CORE Biology (9221) | Variation

🧬 Chapter Notes: Variation (CORE Biology 9221)

Welcome to the chapter on Variation! This is a really important topic because it helps us understand why every living thing, even within the same species, looks slightly different. Think about your classmates—you are all humans, but you don't all look identical!

In this chapter, we will figure out what causes these differences and how scientists categorize them. Don't worry if some terms seem new; we will break everything down step-by-step!

1. Defining Variation

Variation simply means the differences between individuals of the same species. It's the reason why a lion is still recognizable as a lion, but each lion has slightly different size, mane thickness, or hunting ability.

2. The Causes of Variation: Genes vs. Environment

Why do we vary? All differences come from two main places: what you inherit from your parents (your genes) and everything around you (the environment).

Don't worry if this seems tricky at first. Most features are actually a mix of both!

2.1 Genetic Variation (Inherited)

This type of variation is caused by the different genes and alleles you inherit from your parents. Genes are like the instruction manuals for your body.

• Key Cause: Inherited characteristics passed down through reproduction.
• Examples of Genetic Variation:
  • Eye colour (blue, brown, green).
  • Blood group (A, B, AB, or O).
  • Inherited diseases (like sickle cell anemia).
  • Natural shape of your earlobes (attached or free).

Did you know? Even identical twins, who have the exact same genes, can show minor differences in weight or personality because of slight variations during development!

2.2 Environmental Variation (Acquired)

This variation is caused by your surroundings, lifestyle, diet, and training. It is not passed on to the next generation.

• Key Cause: External factors acting on the individual during their life.
• Examples of Environmental Variation:
  • A scar from an accident.
  • Tanned skin due to sun exposure.
  • Skills you learn (like speaking a language or playing football).
  • The size of a plant depending on the amount of light and water it receives.

2.3 Combined Variation (Both Causes)

Most characteristics we observe are influenced by both genes and the environment.

• Example: Height
  • You inherit the genes for being tall or short (Genetic factor).
  • But if you have poor nutrition when you are young, you might not reach your full potential height (Environmental factor).
• Example: Weight
  • Your genes influence your natural metabolism (Genetic factor).
  • But your diet and exercise levels have a massive impact (Environmental factor).

3. The Types of Variation: Continuous and Discontinuous

Scientists organize variation into two main categories, based on how the characteristic can be measured or counted. This is a crucial distinction for your exams!

3.1 Discontinuous Variation

Discontinuous variation refers to characteristics that fall into distinct, clear-cut categories, with no values in between.

• Appearance: Distinct groups (like a switch: ON or OFF).
• Control: Usually controlled by one or a few genes (little to no environmental influence).
• Graphing: Displayed using a bar chart.

Examples of Discontinuous Variation:

• Blood Group: You can only be A, B, AB, or O. You cannot be "half A and half B."
• Sex/Gender: Male or Female.
• Eye Colour: Often simplified into a few distinct categories.

3.2 Continuous Variation

Continuous variation refers to characteristics that can take any value within a range. There are no fixed categories; the differences are gradual.

• Appearance: Gradual range, measurable values (like a sliding scale).
• Control: Usually controlled by many genes (polygenes) AND heavily influenced by the environment.
• Graphing: Displayed using a histogram, which often forms a bell-shaped curve (normal distribution).

Examples of Continuous Variation:

• Height: You can be 1.50m, 1.501m, 1.502m, etc. (Any value is possible).
• Weight, Foot Length, Leaf Width.
• Intelligence (influenced heavily by both genes and schooling/environment).

Comparison Table Summary

Understanding the difference is essential. Use this table for quick revision:

4. The Role of Mutation

If variation is caused by shuffling existing genes, where do new genes and characteristics come from? The answer is Mutation.

4.1 What is a Mutation?

A mutation is a random, spontaneous change in the structure of a gene (or the DNA).

• Imagine a gene is a recipe book. A mutation is like accidentally changing a word in the recipe—this can change the final product (the characteristic/trait).
• Mutations are the ultimate source of new alleles and, therefore, new variation within a species.

4.2 Effects of Mutations

Most mutations have no effect, or they cause harm (like inherited diseases). However, occasionally, a mutation can be beneficial.

• Neutral effect: A change that doesn't affect the organism's survival (e.g., a slightly different hair colour shade).
• Harmful effect: A change that reduces the organism's chance of survival (e.g., causing a debilitating disease).
• Beneficial effect: A rare change that improves the organism's chance of survival or reproduction (e.g., a bacterial mutation that makes it resistant to an antibiotic).

It is these beneficial mutations that are key to the process of evolution, as they give the organism an advantage in the environment.

💡 Summary of Variation

You've done a fantastic job covering variation! Here are the core concepts you must remember for the exam:

Key Points Checklist

• Variation is the difference between individuals in a species.
• Variation comes from Genetic (inherited) or Environmental (acquired) factors, or both.
• Discontinuous Variation involves distinct categories (e.g., blood type) and is mostly genetic.
• Continuous Variation involves a range of measurable values (e.g., height) and is influenced by both genes and environment.
• Mutation is a spontaneous change in a gene and is the origin of all new variation.