its relayed to population gentics ,,natural and artificial selection .the process of evolution and its evidences.the examples in animals and plants

1. Name: Rohama
Roll no : 24
Presented to :
Dr . Faisal

2. SELECTION

3. Outline
• Selection
• Types of selection
• Natural selection
• History of natural selection
• Types of natural selection
• Artificial selection
• Examples in plants and animals
• Opposite mechanisms of evolution

4. Selection
Selection, in biology is the
 preferential survival and reproduction
 preferential elimination of individuals with certain genotypes
By means of :
 natural selection
 artificial selection

5. Natural selection
• Natural selection is the differential survival and reproduction of
individuals
• Natural selection is one of the basic mechanisms of evolution,
along with
 mutation
 migration
 genetic drift

6. Concept of selection
• The theory of natural selection was given by
 Charles Darwin
 Alfred Wallace
• who described it as
‘survival of the fittest’
“Adaptations and natural selection is the process of evolution”

7. History
• The concept, published by Darwin and Alfred Russel Wallace in a
joint presentation of papers in 1858
• Was elaborated in Darwin's influential 1859 book
• On the Origin of Species by Means of Natural Selection,
• With the discovery of Genetics by Gregor Mendel
• The mechanism of natural selection became even clearer

8. Darwin's observation

9. The Process of Natural Selection
• Variation Organisms (within populations) exhibit individual variation
in appearance and behavior.
• Inheritance. Some traits are heritable, whereas other traits are
strongly influenced by environmental conditions .
• High rate of population growth. Most populations have more
offspring each year than local resources lead to struggle for resources.
• Differential survival and reproduction Individuals possessing
traits well suited for the struggle will contribute to the next
generation.

11. Types of naturel selection
There are several ways selection can affect population variation:
stabilizing selection
directional selection
diversifying selection
sexual selection

12. Stabilizing selection
• Natural selection favors an average phenotype
• By selecting against extreme variation
The population will undergo stabilizing selection

13. Example
Human skin color
• Most humans are not extremely light skinned or extremely dark
• The majority of the species fall somewhere in the middle

14. Directional selection
• When the environment changes, populations will often undergo
directional selection,
• Which selects for phenotypes at one end of the spectrum of existing
variation.
• Directional selection occurs when a single phenotype is favored
• Causing the allele frequency to continuously shift in one direction.

15. Example

16. Disruptive selection
• Natural selection can select for two or more distinct phenotypes that
each have their advantages.
• In these cases, the intermediate phenotypes are often less fit than
their extreme counterparts
• The median is not the favorable trait in this case
• This is the rarest of the types of natural selection.

17. Example

18. Sexual selection
• The selection pressures on males and females to obtain matings is
known as sexual selection.
• Sexual selection takes two major forms:
1. Intersexual selection
also known as ‘mate choice’ or ‘female choice’
2. Intrasexual selection
also known as ‘male–male competition’

19. The Good Genes Hypothesis
• The good genes hypothesis states that males develop these
impressive ornaments
• To show off their efficient metabolism or
• Their ability to fight disease.
• Females then choose males with the most impressive traits
• Which they will then pass on to their offspring.

23. Artificial selection
• Artificial selection mimics natural selection in that certain traits are
chosen to be passed down to the next generation
• It is humans that do the selecting of traits during artificial selection.
• Darwin was able to use artificial selection on his birds
• To show that desirable traits can be chosen through breeding

26. Mechanisms of variations opposite to natural
selection
• Genetic drift
• Population bottleneck
• Founder effect
• Mutation
• Migration