Selection and its types and evolution
- 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
- 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