Page 47 - Science Coursebook

3.2 Variation

... continued
4 Put a mark in the appropriate ‘Tally’
column for each wrist circumference
you have measured. Add up all the
tally marks for each row, and write the
number in the ‘Numbers’ column. number
5 Now you are ready to draw a frequency of people
diagram of your results. The wrist
circumference should go on the
horizontal axis, and the number of
people on the vertical axis.
6 Draw bars to show the number of
people in each size range. The bars wrist circumference / cm
should touch each other.
Questions

A1 What is the overall range of wrist circumference in your class (that is, the
smallest and the largest measurements)?
A2 Which wrist circumference is the most common in your class?
A3 Describe any patterns that you can see in your results.

What causes variation?

Why do the people in your class have different sizes of wrist?

Part of the reason is that you have different genes. Your genes determine many
different things about you – such as whether you are male or female, or what colour

hair you have.
Another reason is your environment. This means anything around you that affects

you or the kind of lifestyle that you live. For example, a person who uses their hands
and arms to do heavy work may have very large wrists. Someone who did not get
enough to eat when they were growing up may have very small wrists.

Questions

A+I 2 Suggest two features of humans that are caused by their genes, and are not

affected by their environment.
A+I 3 Suggest two features of humans – other than wrist circumference – that are

affected by both genes and environment.

Summary
• The differences between the individuals in a species are

called variation.
• Variation is caused by genes and by environment.

3 Variation and inheritance 45