The Struggle for survival

1. The Struggle for survival Ms. Muneer

2. Darwin’s Theory Darwin summarized natural selection in these words. “can we doubt (remembering that many more individuals are born than can possibly survive) that individuals having any advantage, however slight, over others, would have the best chance of surviving and procreating their kind?”

3. Darwin’s Theory of Natural Selection is based on some basic observations • Observation 1 • Individuals within a species vary in many ways. • Observation 2 • Some of this variability can be inherited • Observation 3 • Every generation produces far more offspring than can survive and pass on their variations • Observation 4 • Populations of species tend to remain stable in size

4. Natural Selection – 3 Principles • Members of the same species compete with each other for survival • Individuals with more favorable variations are more likely to survive and pass them on. Survival is not random • The favorable variations will become more common. This is Natural Selection.

5. Environment Causes Selection • In England in the early 1800’s , light coloured lichen covered many surfaces, and the peppered moth population was almost entirely of light coloured lichen • Than came the industrial revolution and because of the pollution, the colour of the trees changed • By the late 1800’s the lichen was killed and replaced by black soot from coal burning. • By 1920, peppered moth population was almost entirely composed of black soot individuals

6. Peppered moth White-bodied peppered moth Black-bodied peppered moth

7. Camouglaging The light-colored moth (below the bark's scar) is nearly invisible on this pollution-free tree, camouglaging it from predators

8. Source of Variation • Darwin admitted that a weakness in his theory was that he could offer no explanation for the source of variation. • Six years after Darwin, Gregor Mendel presented his work on garden peas. • Now we understand mutation and recombination is the source of new inheritable variations.

9. Key Terms • Natural Selection: the way in which nature favours the reproductive success of some individuals with in a population over others • It is the survival of the fittest – the organisms that are best able to adapt to the environment will survival and reproduce. • Artificial Selection – directed breeding of animals/plants that exhibit a particular trait

10. Mechanisms of Evolution • Gene pool is the complete set of all alleles contained within a species or population • Not all evolutionary changes are the result of natural selection • Evolution can occur due to catastrophic events • Mutation is the ultimate source of variation in an individual’s gene pool

11. Random Change • Evolution defined in genetic terms as any change in gene (and allele) frequencies within a population or species.

12. Key factors in a Change to a Gene Pool • Small populations - chance fluctuations cause change • Non-random mating opportunities; preferred individuals pass on their alleles in greater numbers than others • Genetic mutation; new alleles are created or alleles are changed • Migration - removes alleles from the population • Natural Selection; individuals with certain alleles have greater reproductive success than others increasing the relative frequency of their alleles

13. Genetic Drift • When populations are small – chance can play a significant role in altering allele frequencies • Change in the genetic makeup of a population resulting from chance is called genetic drift • Genetic drift can lead to a fixation of alleles

14. Genetic Drift in Small Populations

15. Genetic Drift in Small Vs Large Populations

16. Bottleneck Effect • When a severe event results in a drastic reduction in numbers, a population may experience a bottleneck effect • A very small sample of alleles survive to establish a new population • Relative frequencies may differ from original population

17. Northern Elephant Seal Population

18. Bottleneck Effect

19. Founder Effect • When a few individuals from a large population leave to establish a new population • The allele frequencies of the new population will not be the same as the original population

20. Polydactyly

21. Gene Flow • When organism migrate, leaving one population and joining another, they alter the allele frequencies of both • In this way, genetic information is shared between populations. • Unlike genetic drift, gene flow tends to reduce between populations.

22. Natural Selection • Small populations that result from a bottleneck or founder effect are also subject to the effects of genetic drift • This increases the chances that their gene pool will differ from that of the original population • Although genetic drift and bottlenecks can be important in some cases, natural selection is usually the major driver behind changes that result in the evolution of a significant adaptation • Natural selection is the only mechanism known that is able to shape a species to its environment

23. Mutation • Mutations are the only source of additional genetic material and new alleles • Any mutation in a gamete can be passed on to later generations • Since mutations are random changes they are more likely to be neutral or harmful than beneficial

24. Inheritable Mutations Neutral: a mutation that has no immediate effect on an individual fitness or reproductive success Harmful: a mutation that reduces an individual’s fitness Beneficial: a mutation that gives an individual selective advantage, increased reproductive success Fitness– general term referring to lifetime reproductive success of an individual

25. Gene Duplication • Gene duplication occurs when unequal crossing over during meiosis results in an additional copy of one or more genes being inserted into a chromosome • Source of new genes

26. Pseudogenes • Pseudogenes are genes that are duplicated and later lose their ability to be transcribed - they provide strong evidence for evolution • vestigial gene that no longer codes for a functioning protein • The human genome contains thousands of pseudogenes

27. Pseudogene • GULO gene is an example of pseudogene. This gene is necessary for the production of vitamin C. Human and most primates have defective GULO genes http://creation.com/images/pdfs/tj/j21_3/j21_3_118-127.pdf

28. How Common are Mutations? • There is evidence of a rate ranging from 1 in 10,000 cell divisions • In humans, a gene coding for one enzyme used in glycolysis occurs in a single functioning copy and 20 non-functioning pseudocopies