Genetic drift and Mutations. February 4 th 2015

Transcription

1 Genetic drift and Mutations February 4 th 2015

2 Review Broccoli of today are descended from Brassica oleracea. Only the plants with the widest stalks were selected for. What type of evolutionary change does this represent? A) Natural selection B) Gene Flow C) Sexual selection D) Artificial selection

3 Review Broccoli of today are descended from Brassica oleracea. Only the plants with the widest stalks were selected for. What type of evolutionary change does this represent? A) Natural selection B) Gene Flow C) Sexual selection D) Artificial selection

4 Review Artificial and Natural selection both select for certain traits. But in artificial selection, humans select for the traits.

5 Review Suppose there were two populations of elk who were kept separate by a mountain range. Human activity has removed this natural barrier and the two populations interbreed. A) Natural selection B) Gene Flow C) Sexual selection D) Artificial selection

6 Review Suppose there were two populations of elk who were kept separate by a mountain range. Human activity has removed this natural barrier and the two populations interbreed. A) Natural selection B) Gene Flow C) Sexual selection D) Artificial selection

7 Review Although humans were involved in this evolutionary change, there were no traits being selected for. There were however, the exchange of alleles between populations

8 Review Sexual selection can only occur in organisms with distinct sexes. A) True B) False

9 Review Sexual selection can only occur in organisms with distinct sexes. A) True B) False

10 100% white 20% Green 80% White

11 Made a mistake In the case of gene flow, the genetic diversity can increase, but it can also decrease.

12 20% Green 80% White 100% white

13 In conclusion In the case of gene flow, genetic diversity can increase or decrease In the case of natural and sexual selection, the cases we ve mentioned so far, genetic diversity tends to decrease

14 A population of rabbits were black, white and orange. The environment they are in is very snowy all the time. What do you predict will happen to the population? Will the genetic diversity increase or decrease?

15 Learning Objectives Explain random fluctuations in genes may produce changes in genetic frequency Describe how the size of the population may reduce genetic diversity Describe how mutations introduce new traits into a population Explain why mutations are most likely to establish in large populations

16 Activity Time Please pair up with someone send one person to grab a bag of colored paper Activity

17 Instructions The four colours represent the alleles of a gene The pile that you have represents the gene pool (all the alleles) in the population. Please count the number of each allele you have in your population, then calculate the frequency

18 Instructions 10 minutes Now spread the alleles out on your desk, and swipe away about half of the pile Count again and calculate the frequency Repeat three times.

19 Instructions Did evolution happen? Did the allele frequencies change more in a large or small population? What did swiping away half the alleles represent?

20 Genetic Drift Genetic Drift is when allele frequencies change due to chance. There are two types of genetic drift: 1) Bottleneck effect 2) Founder effect

21 Bottleneck Effect When a catastrophic event drastically reduces the population Natural Disasters Habitat destruction Population boom and bust

22 Bottleneck Effect Natural disasters forest fires, climate change, storms, earthquakes, meteorites Habitat Destruction deforestation, pollution Population Boom some populations naturally rise and fall drastically (e.g. locusts)

23 Founder Effect The founder effect happens when a part of the population splits off from the original population, but the allele frequency does not match the original population.

24 Founder Effect We start with the Biology 11 Population. On the ferry to Bamfield (WOO-HOO!) 5 random students (and maybe a student teacher) are stranded on a deserted island. Are the 5 representative of the population?

25 Genetic Drift Changes in allele frequency is much more dramatic in smaller populations than bigger ones.

26 Genetic Drift In a small population, it is much easier to lose alleles by chance.

27 Think about this Genetic variability: Describes the variety of alleles in a population. The more alleles the more genetic variability But what happens when an allele is completely eliminated?

28 If given enough time, the forces of evolution would decrease genetic variability. In other words, we ll have less and less alleles over time. Where do new alleles come from?

29 Mutations Any change in the DNA of organisms. Sun exposure Radiation exposure Natural causes

30 Video 0:00 2:10

31 Mutations Mutations are produced from mistakes in DNA repair Mutations in sex cells lead to entirely new alleles in offspring These new alleles can produce entirely different traits that can increase fitness, or decrease fitness

32 Mutations The DNA is broken. The break can be produced by radiation chemicals or simply natural process.

33 Repair enzymes repair the DNA. But does not always do so correctly. In doing so, they can create entirely new alleles.

34 Thus new alleles are born. These new alleles can code for very Different features than the original allele.

35 Albinism is caused by Mutations in the gene that code for pigmentations Hairlessness is also Caused by natural Mutations that were Then selected for.

36 But keep this in mind Mutations happen 1/10, 000 gametes (eggs/sperm cells) Gametes combine to form an offspring. Meaning 1/5,000 will carry a mutation in a gene

37 It would take 4000 years for a mutation to produce a change in allele frequency of just 1%. Although it is a relatively SLOW mechanism, it is also the only one that creates new alleles.

38 It would take 4000 years for a mutation to produce a change in allele frequency of just 1%. Although it is a relatively SLOW mechanism, it is also the only one that creates new alleles. Without mutations, no new alleles form, and evolution would stop.

39 Learning Objectives Explain random fluctuations in genes may produce changes in genetic frequency Describe how the size of the population may reduce genetic diversity Describe how mutations introduce new traits into a population Explain why mutations are most likely to establish in large populations