Post on 07-Aug-2015
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MEIOSIS
HEREDITY (MENDEL’S THEORY)
NATURAL AND ARTIFICIAL VARIATION AND SELECTION
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.
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.
TYPES OF CELL REPRODUCTION
Mitosis Meiosis
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.
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
IMPORTANCE OF MEIOSIS
Meiosis is a source of genetic variations because it provides new combinations of chromosomes for the resulting gametes.
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
HEREDITY
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.
GREGOR JOHANN MENDEL
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.
MENDEL’S EXPERIMENTS
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.
MENDEL’S FIRST EXPERIMENT
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.
SECOND EXPERIMENTDIHYBRID
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.
Natural Selection
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.
Artificial Selection
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.
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.