igcse biology chapter 18 variation class presentation

1. 18 Variation and
Selection
18.1 Causes and types of variation
ppt 1

2. We belong to the same species; Homo sapiens.
We share many similar features, but we are not exactly the same.
Differences between individuals of the same species is called
variation.
Variation

3. Terminology
• Phenotype = the observable features of an
organism
• Genotype = the genetic make-up of an organisms

5. Which features are caused by the gene’s the person has (inherited),
and which ones are caused by the environment (acquired)?

6. Or
Genotype + Environment = Phenotype

10. Limited number of phenotypes with no intermediates. Usually caused by
genes alone (genotype).

13. Range of phenotypes between two extremes. Usually caused by both
genetic and environmental factors

15. Class work…
• Access the Google sheet
https://docs.google.com/spreadsheets/d/1s5rHLzWn6z
nk-rgg2QhEJlcY-z5eTytdREnDhLDNs6I/edit?usp=sharing
• Record class data on;
Height
Index finger length
Shoe size
Attached or free ear lobes
Widows peak
Ability to roll tongue
• Use the data to draw one bar chart, one pie chart and
one histogram.

16. height category / cm tally frequency
140 – 144
145 – 149
150 – 154
155 – 159
160 – 164
165 – 169
170 – 174
175 – 179
Investigating Continuous Variation
• Place the heights of students in your class in the tally chart below.
• Work out the frequency of each category.
• Draw a histogram to display your results.
1 What is the modal (most common) height of people in your class?
2 Height is an example of what sort of variation?
3 What causes this sort of variation?

17. Homework…
• Read textbook pages 232/233
• Read through and complete booklet pages 3/4.