Overview

1. EVOLUTIONRANDOM CHANCE“The theory of evolution says that life originated, and evolution proceeds, by random chance.”-Wallace

2. Overview • Evolution has allowed for humans to evolve from apes or chimpanzees into the complex and intelligent species we are today. • Through the random nature of genetic drift, gene flow and mutations evolution is continually advancing and developing. • Through this presentation genetic drift, gene flow , mutations and types of mutation will be investigated to show how evolution is reached through these processes.

3. Overview Cont’d • Genetic Drift • Genetic Drift and It’s Affect on Population Size • Genetic Drift and the Reproducing Population • Types of Genetic Drift -Bottleneck and Founder • Problems Caused By Genetic Drift • Gene Flow • Gene Flow and Genetic Variation • Mutations • Are All Mutations Bad • Types of Mutations • Summary • Reading • Questions • Bibliography

4. Genetic Drift • Genetic drift is a random process that is one of the most important mechanisms of evolution. Genetic drift allows for evolution to occur by helping to increase and change genes that are present in the gene pool. • Genetic drift is responsible for the random changes in frequencies of genes and alleles within populations and species.

5. Genetic Drift And It’s Effect On Population Size • Genetic drift is greatly affected by population size as it is much more pronounced in small populations than larger populations. • Population size when considering genetic drift doesn’t refer to the amount of people in an area, but refers to the amount of people that are reproducing in an area. • The size of the reproducing population is important because they are the ones who are passing on their genetic information from one generation to another. • The larger the size of population the smaller the effect of genetic drift. For example, if you toss a coin 5 times there is a possibility that all 5 times heads may appear. ( which is symbolic of a gene being lost or fixed) However, if you toss the coin 50 times, it is more likely that heads will appear 50% of the time and tails will appear 50% of the time. (symbolic of relatively equal levels of alleles will be expressed.)

6. Genetic Drift and the Reproducing Population • When individuals pass on their alleles it occurs randomly. This means that a person will not donate exactly the same alleles they posses to their offspring. • When offspring's are produced, only one of the possible two alleles are passed on. • Chance determines which one of the possible two alleles will be used therefore; an offspring receives a combination of alleles from their mother and their father. • Through this process of random chance some alleles may become fixed or lost. Alleles become when they are simply not passed on frequently enough. • A fixed gene means that within a population it is the only allele left.

7. A reproducing population is not passing on equal proportions of all alleles therefore, allele production fluctuates because of random chance. • This is how genetic drift works. On a short term basis genetic drift should keep alleles at random levels because different people are passing on different alleles. However, on a long term basis alleles which have become rare by chance may not be passed at all, or alleles that have become fixed by chance will inhibit other alleles from occurring, therefore decreasing genetic variation.

8. Types of Genetic Drift • There are two types of genetic drift that occur, bottleneck effect and the founder effect. BOTTLENECK EFFECT • This form of genetic drift occurs when a large population experiences an extreme decrease in population size and only a small proportion of the original population survives. • Eventually, the population may recover and grow to their original size again. However, the allele frequencies that were previously present may have been altered because of genetic drift thus posing the possibility of losing or fixing certain alleles.

9. Figure 1 • Severe bottleneck may decrease the chance of evolving because of a decrease in genetic variation. • An example of this type of genetic drift is cheetahs, hundreds of cheetah’s have been studied and there is no allelic variation at all between all the cheetah’s that were studied. Figure 2

10. FOUNDER EFFECT • This form of genetic drift results when a small portion of individuals migrate from a larger population. • The allele frequencies of the new smaller population will be different from those of the original larger population. The difference between allele frequencies in the original population and the smaller population will continue to differ as the small population grows and develops. • An example of the founder effect was when about 30 Amish people in Pennsylvania left a large population and one of the Amish had a recessive trait for shorter limbs and six fingers. The frequency of the short limbs and 6 fingers increased because of the founder effect. Figure 3

11. Problems Caused By Genetic Drift • Without other methods of evolution all populations and species would eventually reach a fixed gene and there would be no genetic variation. • No genetic variation makes evolution nearly impossible for a species. • Other processes which encourage evolution like gene flow and mutation assist in maintaining and increasing genetic variation.

12. Gene Flow • Gene Flow is the movement of alleles from one population to another. • It occurs most commonly when a member from one population reproduces with a member from another population. • Gene flow is caused by an introduction of new genes into a gene pool. This may be caused by migration or short term interaction with another population where reproducing occurs. • Losing or adding people to a population makes changes to gene frequencies within the gene pool.

13. Gene Flow and Genetic Variation • While genetic drift tends to decrease genetic variation, gene flow tends to increase genetic variation. • Gene flow increases genetic variation because new alleles that may be rare and not present at all may be introduced into a new population. • The more gene flow that occurs between populations the more the populations become similar. • If gene flow continued eventually both populations would have relatively the same allele frequencies.

14. Mutations“Although mutation is the ultimate source of all genetic variation, it is a relatively rare event,…” Alaya • Mutations are random changes to genetic code which can be caused naturally or by means of chemicals or radiation. Which produce new alleles for natural selection to act on. • Most mutations occur in somatic cells, these mutations cannot be inherited so they do not have an impact on evolution. • Mutations that do occur in sex cells pose the chance of being passed on to offspring therefore producing new genes in the gene pool and thus creating genetic variation. Therefore, mutations in sex cells have the possibility of impacting evolution. • Mutations are occurring all the time in the body, however DNA has the ability to recognize and repair these mutations before they are passed on to the next generation. On average 1 in every 10 sperm and egg contain a mutation with the possibility of being passed on to the next generation.

15. Usually, an exact copy of a gene is passed down from the parents to the offspring. When a mutation occurs, it means there is a mistake in the coding process of the gene. A mutation can go by unnoticed, or it can have a huge impact on an individual, changing phenotypes. • To explain how mutations can be harmful the English language is used as an example: THE ENEMY IS NOW ATTACKING could be randomly mutated into THE ENEMY IS NOT ATTACKING. Obviously this mutation results in an alteration of what the message was intending to say. Not very often would a random mutation improve what the message was trying to say.

16. Are All Mutations Bad? • Each mutation has the possibility of being beneficial, neutral or detrimental to the organism. • Most commonly mutations are neutral or detrimental as “it is rare that a precision machine is improved by a random change in the instruction for making it.” • Some mutations may be only helpful or harmful in certain environmental conditions. For example the peppered moths mutated from a light color to a dark color around the time of the industrial revolution when the air was sooty, being a beneficial mutation allowing them to survive and reproduce more effectively. • Despite the fact that beneficial mutations don’t occur commonly there are still times when they do occur. The Encyclopedia of Britannica states that these beneficial mutations are “the raw material of evolution.”

17. Although it is rare for beneficial mutations to occur, it does happen. • With the assistance of natural selection a beneficial mutation may become prominent in a population therefore increasing the populations genetic fitness and therefore evolution. It must be kept in mind that a detrimental mutation becomes prominent in the same way. • Beneficial mutations allow for new and more competitive species, better ability to adapt to changes in the environment, diseases and other factors.

18. Types of Mutations • Mutations posing varying effects on individuals and evolution as a whole. There are many different mutations, as mentioned earlier that have the possibility of being neutral, detrimental of beneficial to a species. • There are two different types of mutations, chromosomal and DNA. CHROMOSOMAL MUTATIONS: There are two different types of chromosomal mutations, chromosomal aberrations and chromosomal number changes Chromosomal Aberrations • Inversions: a chromosomal segment that is backwards. For example GAG TAC CAC --> GAG CAT CAC Figure 4 Figure 5

19. Translocation:When a group of genes move within a chromosome or from one chromosome to another. There are different types of translocation mutations. • Reciprocal translocation: When genes move from one chromosome to another. • Non reciprocal Translocation: When one chromosome donates more genes then it receives back. • Transpositional Translocation: When a gene or group of genes moves location within the same chromosome. Figure 6

20. Chromatin Deletions: When a part of the chromosome is deleted. • Chromosome Duplication: Usually results from unequal crossing over, results in a duplicated production of some genes. A very valuable evolutionary mutation as it creates new genes. As gene duplication creates ‘extra’ genes these genes have the ability to mutate without causing harm. Chromosomal Number Changes • Aneuploidy: When one or more chromosomes are missing. • Polyploidy: When there is an excess of chromosomes. Figure 7

21. DNA MUTATIONS: • Point Mutations: Changes in single base pairs of DNA molecules. If the point mutation occurs in a non-coding area of the DNA then it will be neutral or a silent mutation. However, if the mutation occurs in a coding section of the DNA molecule, it can produced a new gene therefore changing the phenotype. It can also be detrimental hindering the normal function of the gene or neutral. • Substitution: When one base pair is substituted for another, generally a neutral mutation. • Insertion and Deletions: Inserting or deleting a base pair of the DNA molecule. Can cause frame shift mutation affecting larger portions of a gene. This form of mutation is usually detrimental and therefore doesn’t commonly encourage evolution. • Inversions: A mutation that reverses a specific nucleotide. Figure 8 There are also translocation mutations in DNA mutations that occur the same way as the chromosomal translocation mutation.

22. Summary • Genetic drift is a process by which random changes in frequencies of genes and alleles occur. Genetic drift causes a increase in genetic variation on a short term basis, but tends to decrease genetic variation over a long term basis. • Gene Flow is the movement of alleles from one population to another and tends to increase genetic variation by introducing new genes into a gene pool. • Mutations are random changes to the genetic code. There are many different types of mutations and each poses the possibility of being beneficial, detrimental and neutral. Mutations that occur in sex cells have the possibility of being passed on through generations and thus creating evolution. • Ultimately, genetic drift, gene flow and mutations drive evolution by increasing genetic variation and gene pools.

23. Reading Listed below is a link to a website which provides detailed information on many aspects of evolution including all the different topics discussed within this presentation. This website is recommended to anybody looking for information on all aspects of evolution. Farabee, M.J (1992-2001) “The Modern View of Evolution” [Online] Available: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookEVOLII.html [2003,June1st]

24. Questions • 1. Explain why genetic drift increase genetic variation over a short period of time, but decrease genetic variation over a long period of time? • 2. Explain what the following quotation is attempting to imply. “It is rare that a precision machine is improved by a random change in the instruction for making it.” Think in terms of beneficial, detrimental and neutral mutations. • 3. How does the random nature of genetic drift, gene flow and mutations play a crucial and important role in evolution?

25. Bibliography Di Guiseppe, Maurice (2003) Biology 12 Toronto: Nelson. Encarta (2003) “Mutations” [Online] Available: http://encarta.msn.com/encnet/refpages/RefArticle.aspx?refid=761563786&para=68#p68 [2003, June 9th] Encarta (2003) “Genetic Drift” [Online] Available: http://encarta.msn.com/encnet/refpages/RefArticle.aspx?refid=761554675&sec=40#s40 [2003, June 9th] Evolution Revolution (n.d) “Genetic Drift” [Online] Available: http://library.thinkquest.org/19926/java/library/article/12a.htm [2003, April 8] Foolish Faith (2003) “Evolution” [Online] Available: www.foolishfaith.com [2003, June 1st] Hyde Q, Margaret (1974) The New Genetics New York: Franklin Watts Moran, Laurence (n.d) “Random Genetic Drift” [Online] Available: http://talkorigins.org/faqs/genetic-drift.html [2003, May 22] Stern, Curt (1902) Principles of Human Genetics United States: Congress Cataloging in Publication Data.

26. Figure 1 Di Guiseppe, Maurice (2003) Biology 12 Toronto: Nelson. Figure 2 McCarten, Niall and Bittman, Roxanne (n.d) “Cheetah Photography” [Online] Available: http://www.cheetahfilmsphotography.com [2003, May 29] Figure 3 Evolution (n.d) “Genetic Drift and the Founder Effect” [Online] Available: http://www.pbs.org/wgbh/evolution/library/06/3/image_pop/l_063_03.html [2003, May 28] Figure 4, 8 Unknown Author (n.d) “Types of Mutations” [Online] Available: http://www.bishops.ntc.nf.ca [2003, June 5th] Figure 5,6,7 Unknown author (n.d) “Mutation: The Source of New Alleles” [Online] Available: http://www.gwu.edu/~darwin/BiSc150/PopGen/Mutation.html [2003, May 22] University of Tennessee (2002) “Genetic Drift and Gene Flow” [Online] Available: http://www.utm.edu/~rirwin/391DriftFlow.htm [2003, April 8] Unknown author (n.d) “Mutation: The Source of New Alleles” [Online] Available: http://www.gwu.edu/~darwin/BiSc150/PopGen/Mutation.html [2003, May 22] Synthetic Theory of Evolution (1997-2002) “Gene Flow” [Online] Available: http://anthro.palomar.edu/tutorials/physical.htm [2003, June 6th] Synthetic Theory of Evolution (1997-2002) “Mutation” [Online] Available: http://anthro.palomar.edu/tutorials/physical.htm [2003, June 6th] Bibliography For Graphics