Variation

Contents

What is variation?

Causes of variation

Investigating variation

Variation quiz

Classifying variation

Variation between species

Variety is the spice of life!

Variation is the differences between different living things.

How many differences between living things can you name?

What causes the differences between species?

Variation between species

Genes are the biological code for different characteristics.Humans have human genes.Bananas have banana genes. Gerbils have (yes, you’ve guessed it) gerbil genes!

Species are different because their genes are different.

Variation within species

No two people are exactly the same. How is this possible?

The current population of planet Earth is more than 6 thousand million people!

Variation within species

Members of the same species also show variation.These differences are called characteristics.

How many human characteristics can you think of that show variation?

What causes each person’s unique characteristics?

Contents

What is variation?

Causes of variation

Investigating variation

Variation quiz

Classifying variation

Variation

Spot the family likeness

Mum Dad

son daughter

Which parent do these children look more like?If the son grows up to have children who might they look like?

Members of the same family often look similar.

Inherited characteristics

Mum Dad

son

Humans, like all living things, inherit characteristics from their parents. How are characteristics passed on?

Why do members of the same family look similar?

daughter

Inherited characteristics

Like all babies, this little boy carries a unique set of genes, half from his mother and half from his father.

This new-born baby’s characteristics are passed in the genes it has inherited from its parents.

Making faces

Causes of variation

But are your characteristics only affected by your genes?

What else will influence the characteristics of this baby as he grows up?

People are different because they inherit different characteristics from their parents.

Causes of variation

Your upbringing and the environment in which you live also affect how you turn out as an adult!

When he gets older, this baby might support a different football team (like Fulham) or not even like football.

Causes of variation

Differences in some characteristics are due to a combination of both inherited and environmental factors.

Name three examples of this type of characteristic.

Your unique characteristics are caused by:

- the unique set of genes you have inherited from your parents

- the environment in which you have developed

Causes of variation

Variation in plants

Plants inherit characteristics through their genes just like humans and other animals.

What characteristics have these plants inherited?

Are plants also affected by their environment?

What causes variation in plants?

Plants are affected by four key environmental factors. Can you name them?

With a little more moisture, light or warmth the size of a plant can double. (Imagine if that happened to us!)

Plants are affected by their environment in a big way!

water

sunlight

temperature

nutrients in soil

What causes variation in plants?

Contents

What is variation?

Causes of variation

Investigating variation

Variation quiz

Classifying variation

Variation

How to classify variation

Characteristics can be classified in different ways.

How would you categorise variation in eye colour?

Could you categorise variation in height in the same way?

Variation in eye colour can be easily categorised in distinct groups. You either have a certain eye colour or you don’t.

Height variation doesn’t fall into separate groups it covers a range of values. Your height changes as you grow.

How to classify variation

A feature that can be measured and given a value from

a range of values shows continuous variation.A feature that cannot be measured but is one of a few distinct options shows discontinuous variation.

Which type of variation are eye colour and height?

continuous variationdiscontinuous variation

Characteristics can be classified into two types:

Continuous or discontinuous?

Continuous variation

What is continuous variation?

This type of feature varies over a continuous range of values.

Examples of continuous variation include mass, height, skin colour, intelligence and leaf area.

Continuous variation is due to the combined effects of genes and the environment.

Does this mean the value of such a feature is fixed or can it change?

Bar chart to show the range of masses in a rugby team

70 80 90 100 110 120 1300

1

2

1

3

4

5

6

weight (kg)

nu

mb

er o

f ru

gb

y p

laye

rs

Continuous or discontinuous?

Discontinuous variation

What is discontinuous variation?

This type of feature can only be one of a few distinct options. Either you have this type of characteristic or you don’t.

Examples of discontinuous variation include blood group, natural eye colour and inherited diseases.

Discontinuous variation the result of genes only.

Bar chart to show the frequency of blood groups in a rugby team

O A B AB0

1

2

3

4

5

6

blood group

nu

mb

er o

f ru

gb

y p

laye

rsDoes this mean the value of such a feature is fixed?

Continuous or discontinuous?

Contents

What is variation?

Causes of variation

Investigating variation

Variation quiz

Classifying variation

Variation

How do we know about inherited variation and how it works?

Meet Gregor Mendel, the first person to trace patterns of characteristics and predict how they were passed on.

Curious about variation

Gregor Mendel1822 - 1884

Surprisingly Mendel was not a scientist but a monk who lived in Czechoslovakia (now called the Czech Republic).

Mendel’s experiments

Mendel was inspired by walking in the monastery garden. He became curious about variation in plants and how characteristics were passed on to new generations.

Another surprising fact about Mendel is that for his ground-breaking work on variation he carried experimentsout on the humble garden pea!

Mendel’s experiments

Mendel chose to experiment on pea plants for two reasons:1. They could be easily grown in large numbers. 2. Their reproduction could be controlled.

Over a period of seven years he experimented on more than 28,000 pea plants!

Why was the pea plant a good choice for his experiments?

Mendel’s experiments

Mendel studied several pea characteristics including:

- pea shape (smooth or wrinkly)

- pea colour (yellow or green)

- pod shape (inflated or constricted)

- pod colour (yellow or green)

- stem length (tall or short)

All these characteristics showed discontinuous variation. Why did this make them easier to study?

Mendel also investigated one characteristic at a time. Why was this important for his experiments to be successful?

Smooth and wrinkly peas activity

Mendel’s results

Mendel’s investigations into seed shape (smooth or wrinkly) produced the following results:

parents:

first generation: x100%

dominant recessive

second generation:

cross-pollination

self-pollination

x

75% 25%

Mendel’s conclusions

Mendel published his work in 1866 and made several conclusions about inheritance:

Certain traits can be dominant or recessive. Recessive traits may

not show but can still be passed on.

Certain traits can be inherited in predictable patterns.

Inherited traits are passed on as bits of information called “factors”. What are these “factors” now called?

Mendel did not know it but he had predicted the existence of genes more than 40 years before genes were discovered!

Father of Genetics

Mendel’s work on the humble pea laid the foundations for modern genetics.

Unfortunately, Mendel published his research in an obscure journal and the importance of his work was not recognised during his life.

Scientists rediscovered Mendel’s work in 1900, sixteen years after he died!

Today, Mendel is famously known as the “Father of Genetics”.Why is he given this grand title?

Contents

What is variation?

Causes of variation

Investigating variation

Variation quiz

Classifying variation

Variation

Variation multiple-choice quiz