Unit 7.3
VARIATION
Variation Within a Species
Exploring how living things can be the same —
but different!
What is Variation?
 Definition: Variation is the differences between
individuals of the same species
 Happens in all living things
 Can be visible (eye color) or hidden (blood
type)
Same Species, Different Looks
 All these animals are goats 🐐
 Same species but different fur, horns, size, and color
Activity 7.3.1 – Measuring Variation in
Humans
 Work in pairs to choose features of your classmates to record such as
Height, Shoe size, Eye color, Arm length.
 Record the data collected from your pair in the form of the table
below:
Name of
the Person
Height
Shoe size
Eye color
Arm length
Using a Bar Chart to Show Variation
Visualizing how living things can vary in color,
size, and more
Recording Data with Tallies
 A girl named Zara studied a plant called kidney vetch. Each plant
had flowers, but not all flowers were the same color. She wanted to
know how many plants had each color.
Activity: Draw a Bar Chart on Your CW copy to represent the data
collected by Zara.
What Causes Variation?
🔬 Two main causes:
1. Genes (DNA) – passed down from parents
2. Environment – things around us like food, exercise, or
sunlight
 🧬 Some traits are caused by both genes and the
environment.
Example – Goats
•
Two goats might have different coat colors → caused by
genes.
•
One goat is fatter than the other → maybe it ate more
food → environment.
 💡 Not all differences are because of DNA.
Types of Variation
You can group variation into:
•
Genetic only (e.g., eye color)
•
Environmental only (e.g., language you speak)
•
Both genetic and environmental (e.g., height)
DNA and Variation
•
Look at the photograph of the goats.
•
What causes the differences between them?
Fertilization and Genetic Material
•
Each goat began life when a sperm cell fertilized an egg cell.
•
Sperm and egg cells contain chromosomes made of genes, which
are made of DNA.
•
Sperm and egg cells contain genes affecting various traits.
•
Different DNA from parents can result in traits like long horns, short
horns, or no horns.
Different Forms of Genes
•
Sperm and egg cells contain different versions of genes
(alleles).
•
These genes affect traits like height, coat color, and tail
shape.
•
Each gene is present in two forms – one from the mother,
one from the father.
Differences Among Siblings
•
Genetic combinations within a species cause
variation.
•
Family members have similarities and differences due
to unique DNA combinations.
Summary on Genetic Variation
•
No two individuals have identical DNA unless they are
identical twins.
•
Siblings have variations due to different inherited
combinations.
Activity – Measuring Wrist Size
👩🔬 You're going to:
•
Measure the wrist size of your classmates.
•
Record the numbers in centimeters.
•
Put the numbers into categories (e.g., 13–14 cm, 15–16
cm)
Think Like a Scientist
•Your data won’t fit into “yes” or “no” answers.
•You’ll need to make categories based on the range of measurements.
•This helps us study variation in a scientific way!
•Record your data in the form of a table given below:
Construct a bar graph based on the data you record
Question to Answer
📝 Think About This: For each variation you studied:
•
Is it caused by genes only?
•
Is it caused by the environment only?
•
Or is it caused by both?