Chapter 5: Variation and Selection

Keywords

1. breeding
2. mutagen
3. mutant
4. mutation
5. selection
6. variation

By the end of this chapter, you will be able to:

a) appreciate that variation in organisms is due to external and internal factors, and that mutations can be beneficial, harmful or neutral.

b) identify diseases associated with genetic disorders, e.g sickle cell anaemia, albinism and Down’s syndrome.

c) understand the concept of natural selection as a mechanism of evolution.

d) understand the use of artificial selective breeding.

Introduction

In this chapter, you will be introduced to the process of variation among members of a specie. If you look around in your class, you will notice that your classmates are all different from you and from other members yet they all belong to the same species.

They vary in such aspects as their height, size, shape of the face, color of their skin and so on. up of an You will appreciate that this variation could result from environmental genetic sources; the main cause being mutation (sudden change in genetic make organism).

You will also identify diseases associated with genetic disorders and understand the concept of natural selection as a mechanism of evolution. You will then appreciate the use of variation in selective plant and animal breeding for better varieties with superior qualities like high yielding, disease and resistance.

5.1 Variation in organisms

In this activity you are going to explain the meaning of variation.

Activity 5.1 Explaining the meaning of variation

Key question

What is variation?

What you need

Computer with internet connection

Notebook

Pen

Biology textbook

What to do

1 In groups, research and discuss on the meaning of variation.

2 Give examples of variation due to environmental and genetic factors.

3 Share your findings with the class.

4 Harmonise and pin up on the class noticeboard.

5.2 Mutations

Mutations are sudden changes in the genetic composition of organisms. They result in new genes and therefore variations in organisms. Some mutations may be beneficial, neutral or even harmful.

Mutations can occur on their own or can be induced by exposing living things to X-rays, ultraviolet rays, radioactive chemicals and nitrous acids. These are known as mutagens. Organisms in which mutations have occurred are known as mutants, In this activity you are going to explain the significance of mutation.

Activity 5.2 Explaining the significance of mutation

Key question

What is the significance of mutation?

What you need

Computer with internet connection

Biology textbook

Notebook Pen

What to do

1 In your groups research on and discuss mutations.

2 Make a write-up explaining the significance and examples of:

1. beneficial mutations
2. neutral mutations
3. harmful mutations

3 As a group present your findings to the rest of the class.

5.3 Genetic disorders

In the previous activity, you have researched about mutations and how they come about. Mutations can be harmful to organisms causing disorders that can stand out. The disorder if it occurs in sex chromosome, it can be passed on to the next generation. In the next activity, you are going to research and discuss the genetic disorders in humans.

Activity 5.3 Investigating genetic disorders in humans

Key question

What are genetic disorders?

What you need

Computer with internet connection

Notebooks

Pictures of different genetic Pen disorders Manila paper • Biology textbook Marker

What to do

1 Study the pictures or images of the different disorders.

2 Identify the disorders.

3 Describe the disorders and their causes.

4 Make a write-up and share the information with your class.

5 Harmonise and pin up the corrected version on the class noticeboard.

5.4 Natural selection

In the population some organisms are better adapted to their environment. They are able to survive and reproduce and leave many offsprings, while some do not survive or they are eliminated. Natural selection is the principle mechanism of evolution. In the next activity, you are going to research on the process of natural selection.

Activity 5.4 Investigating the process of natural selection as a mechanism of evolution

Key question

1 What is natural selection?

2 How does natural selection lead to evolution?

What you need

Computer with internet connection

Biology textbooks

Notebook

What to do

Pen Manila paper

Marker

1 In groups, research and discuss meaning of natural. selection and how selection of beneficial variation results in evolution.

2 Make a write-up of your findings and present it to the class.

3 Harmonise your information and pin it up on the class noticeboard.

5.5 Evolution

In the previous activity you have discussed natural selection. In the next activity, you will discover through research that evolution is favoured by natural selection.

Activity 5.5 Investigating the process of evolution

Key question

What is evolution?

What you need •

Computer with internet connection •

Pen Biology textbook

Manila paper

Notebook

What to do • Marker

1 In groups, research and discuss the process of evolution.

2. Make a write-up of what evolution is and then present it to the class

3 Harmonise your information and pin it up on the class noticeboard.

5.6 Artificial selection and selective breeding

After studying the benefits of natural selection, the scientists realised that characteristics in both plants and animals could become more frequent in they can speed up the process and guide the selection so that desirable plants and animal populations. By doing this, they were able to improve their crop yields. In Activity 5.6, you will research and discuss the methods used to breed plants and animals of desirable characteristics.

Activity 5.6 Discussing the methods used to breed plants and animals of desirable characteristics

Key question

What are different methods used in artificial selection?

What you need

Computer with internet connection

Pen

Biology and Agriculture textbooks

Manila paper

Notebook

Marker

What to do

1 In groups, research and discuss artificial selection and the methods used.

2 Write down the definition of artificial breeding and the different methods used.

3 Visit or talk to the veterinary doctor.

listen to the discussion or his/her presentation.

ask questions to clear any misunderstandings and present it to the class.

Write a report.

4 Report your findings to the class.

5 Harmonise your information and pin it up on the class noticeboard.

5.7 Genetic plants and animal breeding

Plant and animal breeding involves crossing of individuals of desired qualities to result in hybrid organisms that have desired qualities of both parents. Such qualities include quick growth, drought resistance, disease resistance, and high yield.

This requires the knowledge of genetics. In the next activity you are going to find out the use of genetics in plants and animal breeding.

Activity 5.7 Variation and Selection Finding out the use of genetics in plants and animal breeding

What you need

Computer with internet connection

Biology textbook

What to do Notebook

Pen

1 Listen to and interact with the Agricultural Extension Officer invited to talk about the use of genetics in plant and animal breeding.

2 Ask questions to enhance understanding.

3 Write a report and share it with the class.

4 Harmonise your report.

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