Chapter 4: Inheritance

Keywords

1. anaphase
2. bivalent
3. centriole
4. centromere
5. chiasma
6. chromatid
7. chromosome
8. cleavage
9. homozygous
10. inheritance
11. interphase
12. linkage gaps
13. meiosis
14. metaphase
15. nuclear
16. membrane
17. offspring

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

a) understand the process of cell division and significance of meiosis.

b) understand the concept of inheritance using genetic diagrams.

c) understand and explain sex determination in humans.

d) understand and explain sex linkage in humans.

Introduction

In the previous chapter, you learnt about sexual reproduction in humans where you discussed how human beings produce others of the same kind. However, you must have noticed that people vary in some characteristics and resemble in others even in the same family. How does this come about?

In this chapter, you are going to learn that there are factors that bring about these new characteristics in related people. What they come out to be and what makes them a certain kind is determined by factors that they inherit from their parents. You will appreciate that through the process of heredity children acquire characters from their parents.

Cell division processes

New cells only come into existence by the division of already existing cells. This follows a series of stages each with unique events. New body cells are formed by the process of mitosis while reproductive cells are formed by meiosis. In Activity 4.1 you are going to find the stages of the process of meiotic cell division.

The process of meiosis follows a series of stages each marked by specific changes. These changes can be used to identify them and to distinguish them from one another.

Activity 4.1 Finding out the stages of the process of Meiosis/Meiotic cell division

Key question

What occurs in the different stages of meiotic division?

What you need?

Biology textbook

Notebook •

Pen

Computer with internet connection •

Animation on meiotic cell division

Pencil and a rubber

What to do

1 In your group watch an animation on meiotic cell division.

2 Using your observations and by research, identify the stages of meiotic cell division in their correct sequence.

3 Describe what occurs at each phasel stage using diagrams and short notes in your notebooks.

4 Explain the significance of meiotic cell division in maintaining the chromosome number.

5 Share your findings with the class harmonise and pin up on the das noticeboard.

4.2 Concept of inheritance using genetic diagrams

Genetics is a branch of Biology that deals with patterns of inheritance one understands the many terms used in its study. In this activity you are going to find out the meaning of several listed genetic terms used in genetics.

Activity 4.2 Finding the meaning of terms used in genetics

Key question

What are the common terms used in genetics?

What you need

•Biology textbook

Computer with internet connection

Materials for creating your own visual aids, e.g. manila papers

Different markers

Pens •

Colored chalk.

What to do

1 In your group research for the meaning of the following terms: chromosome, gene, dominant, recessive, trait, allele, hetorozygous, homozygous offspring heterozygotes, homozygous, phenotype and genotype

2 Share what you understand on the meaning of the terms with the whole class.

Inheritance occurs when male and female gametes fuse forming a zygote which then grow into an offspring containing a blend of characters of both parents. In this next activity you are to simulate how this process occurs.

Activity 4.3 • Demonstrating how inheritance occurs

Key question

How does inheritance occur?

What you need

Beads of two contrasting colors e.g. black and white (beads of different colors or any other medium-sized seeds can be used).

Containers e.g. beakers, plastic cups, tin Notebook •

Pens

Pencil

Rubber

Biology textbooks

Computer with internet connection.

What to do

1 In a group research on inheritance. Inheritance

2 Develop an activity using the coloured beads (or alternative items) provided to demonstrate inheritance.

3 Explain the concept of inheritance to the rest of the class.

Activity 4.4 To demonstrating inheritance of a trait

Key question

How is a trait inherited?

What you need

Notebook

Pens

Pencil

Rubber

What to do

Biology textbook

Computer with internet connection

Manila paper and marker

1 In a group research and discuss how to make genetic crosses to show the offspring from a cross between a tall father and a short mother.

2 Explain results of a cross and share with the rest of the class (in crossing between two different traits it is the dominant allele that determines the phenotype of an offspring that is heterozygous).

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

4.3 Sex determination in humans

The sex of a child is determined by the sex chromosomes known as X and Y-chromosomes. Sex of the offspring depends on the sex chromosome present in the sperm that fuses with the ovum at fertilisation, since sperms can have either an X or Y chromosome and ova have only X chromosomes.

Activity 4.5 Explaining sex determination

Key question

How is sex determined?

What you need

• Pen

• Pencil

• Ruler

• Computer with internet connection

Biology textbook

What to do

1 In your group research on sex determination in humans.

2 Discuss amongst yourselves and explain the meaning of sex determination.

3 Using annotated diagrams, explain how sex determination occurs in humans.

4 Share your findings with the rest of the class.

4.4 Sex linkage in humans

The X chromosomes also carry other genes that determine other characteristics of the offsprings and these are inherited along with the sex hence they are linked to sex chromosomes and known as sex linked genes. In Activity 4.6, you will research and discuss on sex linkage in humans.

Activity 4.6 Investigating sex linkage in humans

Key question

How does inheritance of sex linked characters occur?

What you need

Pen

pencil

Computer with internet connection

Biology textbook

Manila paper

Notebook

Marker Ruler

What to do

1 In groups, research and discuss sex linkage in humans.

2 Make a write-up of what you understand by sex linkage in humans.

3 Using examples explain how sex linkage occurs in humans.

4 Report your findings to the class. 5 Harmonise your findings and pin the work on the class noticeboard.

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