University of Guyana Science Presentation

1. MEIOSIS
HEREDITY (MENDEL’S
THEORY)
NATURAL AND ARTIFICIAL
VARIATION AND SELECTION

2. KEY TERMS
 Cells: the basic unit of structure in the of structure in living things that can carry on all life functions.
 Chromosomes: structures composed from DNA that contain cells (genetic material)
 Diploids: Cells that have the full number of chromosomes in homologous pairs
 Gametes: the sperm and egg cells or sex cells that combine to form a zygote during fertilization.
 Haploids: cells that have the normal number of chromosomes.
 Spores: a reproductive structure with a protective covering formed from non living matter; E.g. mud
created toads and frogs.

3. CELL REPRODUCTION
Cell reproduction is the process by which cells
produce more cells. Cell reproduction is very
pertinent for growing, repairing dead cells and
producing new organisms.

4. TYPES OF CELL REPRODUCTION
Mitosis Meiosis

5. CHARACTERISTICS OF MEIOSIS
Cells in the testes and ovaries
divide by meiosis.
Meiosis produces cells that are
not genetically identical.
Meiosis have only half of the number of
chromosomes as the original cells.
In meiosis the cells divide twice.

6. STAGES OF MEIOSIS
Four chromosomes in the
nucleus
Each chromosome duplicates
itself
Cells divide into two
Cells divide again to form four
sex cells with only two
chromosomes

7. IMPORTANCE OF MEIOSIS
Meiosis is a source of genetic variations because it provides new
combinations of chromosomes for the resulting gametes.

8. COMPARISON BETWEEN MEIOSIS AND MITOSIS
FEATURE MITOSIS MEIOSIS
Number of cell division 1 2
Number of cells formed 2 4
Number of chromosomes
in cells formed Same as original cell
(diploid)
Half the number of
original cells (haploid sex
cells)
Types of cells formed Body cells Sex cells
Genetic variation in cells
formed
None Variation

9. Heredity is the passing of traits to offspring
from its parents or ancestor. This is the process
by which an offspring cell or organism
acquires or becomes predisposed to the
characteristics of its parent cell organism.

10.  Mendel worked out the main rules of inheritance.
Many others had studied the inheritance of trait
earlier, but Mendel blended his knowledge of science
and mathematics and was the first one to keep count
of individuals exhibiting a particular trait in each
generation. This helped him to arrive at the laws of
inheritance.

11.  Mendel used Pea plant for his experiment, which are
usually self pollinating even when they are alone. He
selected pea plant so that he could control and change
their self-pollination to cross-pollination. He called
them ‘P’ generation.

12.  At first Mendel cross-pollinated short and tall
pea plants of pure breed.
When the plants of F1 generation were fully grown
he allowed them to self pollinate.

15. Natural Selection
 Natural selection is Darwin’s most famous theory;
 Individuals with characteristics which increase their probability of survival
will have more opportunities to reproduce and their offspring will also
benefit from the heritable, advantageous character.

16. Natural Selection

17. Artificial Selection
 Artificial selection is the intentional reproduction of individuals in a
population that have desirable traits.
 A process in the breeding of animals and in the cultivation of plants by
which the breeder chooses to perpetuate only those forms having
certain desirable inheritable characteristics.

18. Artificial Selection

19. SIMILARITIES AND DIFFERENCES
Similarities
 Both natural and artificial
selection reduces changes in
living organisms.
Differences
 The selective force of natural selection
is the environment while the agent of
change in artificial selection arises
from human.

20. REFERENCES
Coble C.R, Fichter G.S et al. (1980) Life Science.
New Jersey. Prentice-Hall Inc. pp. 358-361.
Hallman R. (2001) Reviewing The Living
Environment: Biology. New York. Amsco
School Publications Inc. pp 100-102.