Introduction. Let s try this again. Do you change during your lifetime? Do you evolve??

Transcription

1 Introduction Let s try this again Do you change during your lifetime? Do you evolve??

2 What questions couldn t Darwin answer? What if he could have called Mendel as a lifeline?

3 Population genetics was born in the 1930 s. Darwin s ideas + Mendel s + a few others = the Modern Synthesis, or Neo-Darwinism. This explained variation and natural selection in terms of genes.

4 The Modern Synthesis emphasizes: (1) the importance of populations as the units of evolution, (2) the central role of natural selection as the most important, but not the only, mechanism of evolution, and (3) the idea of gradualism to explain how large changes can evolve as an accumulation of small changes over long periods of time.

5 2. A population s gene pool is defined by its allele frequencies Define population for me again What s a gene pool? Where did the Hapsburgs go swimming?

6 What would the term gene frequency mean? Hint: it means we are going to do some more math. For example, Freq. Of R = 80%, or.80» And Freq. Of r = 20%, or.20 We now define evolution simply as a change in gene frequencies in a population over time.

7 3. The Hardy-Weinberg Theorem describes a nonevolving population The Hardy-Weinberg theorem describes the gene pool of a nonevolving population. The shuffling of alleles during meiosis and random fertilization should have no effect, like shuffling a deck of cards doesn t change the deck, just the combination of which cards are next to which, and which hands get dealt. We are all dealt a different hand when we are conceived. It shouldn t change the gene frequencies or the genotype frequencies. So let s do some math. Mind your p s and q s!!!!!

8 Here is when a population is said to be in Hardy- Weinberg equilibrium (in other words, it is not evolving). Let s say we look out and see a field of flowers and count the red (dominant) and the white (recessive), and get these numbers: Red 960 White - 40

9 p =??? q =???? The combined frequencies must add to 100%; therefore p + q = 1 If p + q = 1, then p = 1 - q and q = 1 - p. Makes sense, yes? Now let s take it the next level

10 What is the probability of generating an RR offspring? In our example, p = 0.8, so p 2 =??? The probability of generating an rr offspring is? In our example, q = 0.2 and q 2 = The probability of generating Rr offspring is???. In our example,????.

11 The genotype frequencies should also add to 1: p 2 + 2pq + q 2 = 1 For the wildflowers, = 1. This general formula is the Hardy-Weinberg equation. So if we can only see or test for phenotypes, where do we start to figure out these p s and q s??? Let s practice: How many of you can roll your tongue? How about a worksheet?

12 Hardy and Weinberg described evolution like this: 5 things must be true of a population for its gene and genotype frequencies to stay the same (for it to not evolve) (1)Very large population size. Why??? (2) No migrations. Can genes flow??? (3) No net mutations. Simple math, yes? (4) Random mating. Examples?? (5) No natural selection. What is different about this agent of change compared to the other ones?

13 2. The two main causes of microevolution are drift and natural selection Five total evolution causers: genetic drift the change happens by chance natural selection gene flow - migration Mutation Non-random mating These can cause the frequencies to change. It s all math!

14 Students will explain and/or describe the scientific mechanisms, such as genetic drift, gene flow, and nonrandom mating, resulting in evolutionary change.

15 Students will explain and/or describe how mutation and genetic recombination increase genetic variation.

16 Let s emphasize this again: Natural selection is the only factor that generally adapts a population to its environment. Selection always favors the disproportionate propagation of favorable traits. The other four may effect populations in positive, negative, or neutral ways.

17 Genetic Drift: Chance changes in small populations Here are some neat examples: The Founder Effect: American Amish The Bottleneck Effect: Ashkenazic Jews Let s look at a model of migration compared to genetic drift. Draw a circle with R s and r s in it to model a population.

18 Now let s address some confusing lists What causes variation? What causes evolution? Does anything cause both? Does anything that causes one play a role in the other? Let s compare lists of evolution causers variation causers and steps in the natural selection process.

19 Students will explain and/or describe how mutation and genetic recombination increase genetic variation.

20 2. The effect of selection on a varying characteristic can be directional, diversifying, or stabilizing So these are patterns of change we see caused by natural selection. directional selection, diversifying selection, or stabilizing selection.

21 Directional selection is the most common type. Giraffe s necks, Kettlewell s moths, eg. Fig

22 Diversifying selection might lead to Fig

23 Stabilizing selection reduces variation and maintains the predominant phenotypes. Human birth weight is subject to stabilizing selection. Babies much larger or smaller than 3-4 kg have higher infant mortality. Let s look at one more misconception..

24 SC.912.L.15.10: Identify basic trends in hominid evolution from early ancestors six million years ago to modern humans, including brain size, Jaw size, language, and manufacture of tools.

25 Natural selection cannot fashion perfect organisms, even though some are really neat! Evolution is limited by historical constraints. Evolution does not throw away old parts and build new ones from scratch. Evolution tinkers with what already exists, and it ends up doing a different job. Hence the arm bones in the fin of a whale and my aching back. They aren t perfect, but they survived selection. Ken Miller s tie clip is a what? Here, chapter 24. Need to put an air conditioner somewhere? Tinker!

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27 2. Adaptations are often compromises. For example, because the flippers of a seal must not only allow it to walk on land, but also swim efficiently, their design is a compromise between these two functions. Similarly, human limbs are flexible and allow versatile movements, but at the cost of injuries, such as sprains, torn ligaments, and dislocations.

28 3. Not all evolution is adaptive. Chance affects the genetic structure of populations to a greater extent than was once believed. For example, the Amish.

29 If a hypothetical colony of 100 humans isolated themselves on an island, after several generations, their genetic makeup would be determined by: A. genetic drift B. a bottleneck C. sexual selection D. the founder effect

30 Of the following, which best illustrates natural selection? A. An organism with favorable genetic variations will tend to survive and breed successfully B. A population monopolizes all of the resources in its habitat, forcing other species to migrate C. A community whose members work together utilizes all existing resources and migratory routes D. The largest organisms in a species receive the only breeding opportunities

31 A small population of chimpanzees lives in a habitat that undergoes no changes for a long period of time. How will genetic drift probably affect this population? A. It will accelerate the appearance of new traits B. It will reduce genetic diversity C. It will promote the survival of chimpanzees with beneficial traits D. It will increase the number of alleles for specific traits

32 A small population of chimpanzees lives in a habitat that undergoes no changes for a long period of time. How will genetic drift probably affect this population? A. It will accelerate the appearance of new traits B. It will reduce genetic diversity C. It will promote the survival of chimpanzees with beneficial traits D. It will increase the number of alleles for specific traits