1. Gr.12 Life Sciences
Meiosis

2. Daughter cells - new cells produced by cell division
Definition of Terms
Meiosis – cell division whereby a diploid cell(somatic cell)undergoes two cell divisions to form four dissimilar haploid cells( sex cells)
Chromosomes - cell parts that determine what traits a living thing will have
Chromatid - one strand of DNA; after replication, a chromosome is made up of two identical Chromatids
Daughter cells - new cells produced by cell division

3. The Process

4. Where does it take place…

5. THE SIGNIFICANCE OF MEIOSIS
The process of meiosis reduces the number of
chromosomes by half ( diploid to haploid)
Meiosis is the process through which gametes are produced ,
and are prepared for fertilization
Meiosis ensures that the number of chromosomes in species stays constant over generations
Meiosis is important to introduce genetic variation though:
- Crossing over ( Prophase 1)
Random arrangement of chromosomes at the equator ( Metaphase )

6. How chromosomes are arranged…

7. ABNORMAL MEIOSIS -Down Syndrome

8. Spindle fibre fails to separate during meiosis
NON -DISJUNCTION
Spindle fibre fails to separate during meiosis
Members of one pair of homologous chromosomes fail to become separated during Anaphase 1 and may happen in Anaphase 2
2 gametes receive extra copy of affected chromosome
2 gametes lack that chromosome

9. Non-Disjunction continued…

10. COMPARISON OF MITOSIS AND MEIOSIS
Site where it occurs
Somatic cells
Ovaries and testis
Ovules & anthers
Purpose of process
Growth
Formation of haploid gametes
No. of daughter cells produced
Two identical cells
4 haploid cells genetically different
No. of divisions
One nuclear division
Two nuclear divisions

11. Practical activity
Meiosis song

12. ACTIVITY 1
The following diagram represents a phase of meiosis. Answer questions based on this diagram.
1. Write down the term that best describes the paired
chromosomes labelled A (1)
2. Identify structure B (1)
3. How many chromosomes are shown in the diagram
above? (1)
4. How many chromosomes would be there in each
cell at the end of meiosis? (1)
5. Give two significance of meiosis. (2)

13. Answers to Activity 1 Homologous √ (1)
2. Spindle threads / fibre √ (1)
√ (1)
4. 2 / Half √ (1)
5. -To reduce the number of chromosomes from diploid
to haploid √
- for the production of gametes √
- introduce genetic variation
- keep the number of chromosomes the same throughout
generations any x (2)

14. Activity 2 Study the following diagram and answer questions.
Provide labels for part A - D on the diagrams a
alongside (4)
2. Name the process in meiosis that is illustrated on
this diagram (1)
3. Name ONE importance of the process mentioned
in question (1)
4. Draw the structure of the diagram labelled A to
show its appearance immediately after the
process mentioned in question (2) C B A D

15. Answers to Activity 2 A- Chromosome (1) B- Centromere (1)
C- Chromatid (1)
D- Chiasma (1)
2. Crossing over (1)
3. To bring about genetic variation (1)
diagram –(1)
- different shades- (1) P

16. Activity 3
The diagram below represents an animal cell in a phase of meiosis.
State which phase of meiosis is represented in the
diagram. (1)
2. Give a reason for your answer to question 1. (2)
3. How many chromosomes:
(a) were present in the parent cell before it
underwent meiosis (1)
(b) will be present in each cell after meiosis (1)
4. Where does meiosis take place in :
(a) Humans (1)
(b) Plants (1)
5. Could the cell represented in the diagram be that
of a human. (1)
6. Give a reason for your answer to question 5. (2)

17. Activity 3 Answers 1. Anaphase 2 √ (1)
2. Chromatids are pulled towards the poles. √ (1)
3. a – 4 √ (1)
b – 2 √ (1)
4. (a) – Ovaries and testes √ (1)
(b) – Ovaries and anthers √ (1)
5. No √ (1)
6. Humans would have 23√ chromosomes/ 46 chromatids in this phase (2)
In this diagram only 4 √chromosome/ 8 chromatids are shown in the
diagram.

18. Activity 4

19. Activity 4 Answers