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Biology: Population Genetics: Darwin Meets Mendel


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About this Lesson

  • Type: Video Tutorial
  • Length: 9:24
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 101 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Final Exam Test Prep and Review (42 lessons, $59.40)
Biology: Population Genetics and Evolution (15 lessons, $20.79)
Biology: The Hardy-Weinberg Theory (6 lessons, $9.90)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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Did you ever wonder how did we have biology before Charles Darwin? When you think of what the theory of natural selection, thus the theory of evolution has done for our perspective on the why of biology, and the why of what things are you got to say to yourself what happened before the mid-1800s. And I don't want to suggest to you that there was no biology that was done back before that - some of it was wrong, as we've come to find out, but the bottom line is there was some. But, you know, when you put together the ideas of Charles Darwin and Gregor Mendel, and look at them in their entirety, it just gives you such a working template for understanding our planet - it's incredible.
Let's talk a little bit about what Darwin - what his general contribution was. And you know it comes back to this. No matter what you talk about in biology, you can always bring it back to natural selection.
What did Darwin say? Well, to paraphrase the theory of natural selection, evolution proceeds with natural selection acting on variation. Evolution proceeds with natural selection acting on variation. In other words, you get variations, and natural selection happens. Why? Because some of the variations survive. So to make an explanation of this we have variations, and these variations happen within individuals - that's important - within individuals - individuals vary. Usually this gives them some kind of reproductive advantage, doesn't it? And it might make them bigger, stronger, faster, better looking, whatever - reproductive advantage.
So they did a reproductive advantage; and therefore, we have a mechanism of selection. So, it lets you know why. The selection to pass on their genes and now the idea that when these individuals are selected for you begin the changing of the population. The population changes so you're saying yeah so what. But, right here brings us to the idea of when Darwin met Mendel. You see because here's the thing. Evolution seems to be a population phenomena if we consider that evolution is a phenomena of populations, the driving force behind this population change is variation, and who gave us all our knowledge of why variation happens - Mendel because that's an individual phenomena. So Darwin, leading Mendel is big time. In fact, it's amazing some of the things we can talk about here. You know, Darwin knew about change. Darwin looked at things and said wow! - change happens, variation happens but he didn't know about genetics. He didn't know about alleles, he didn't know about chromosomes, he didn't know about - Mendel didn't know about chromosomes, but he didn't know about any of those things that had to do with genetic traits.
Let me give you a little equation I think I'm going to make up here we'll call it Wolfe's equation. Darwin + Mendel gives you an understanding of evolution. Now, let me tell you an interesting story and it will give you an idea of how all of this fits together. When Mendel's work first broke in the beginning of the twentieth century - you remember Mendel was buried for 40 years - nobody knew any of his work. But when his work first came out in the beginning of the twentieth century, it actually, to the Mendelians they said this really flushes Darwin's theory of natural selection down the toilet. There's a big contradiction between the idea that Mendel's theory and Darwin's theory seem not to go hand-in-hand. The Darwinian's thought was like this - that we looked at variations in gradations. Darwin was into what we call "Quantitative Characteristics." You know that quantitative characteristics are those that are concerned by polygenic inheritance. And we'll come back to that chart later with the skin color and show how that particular chart shows us how you may get gradations because Darwin and Mendel didn't know about quantitative characteristic inheritance. What Darwin said was, but look, we have to talk about a continuum. We have to talk about the fact that evolution - that natural selection happens when you have a continuum of events. For example, color shades. You know Darwin would say well this one of this color shade has a greater opportunity for survival - fur length. You know if its fur is this long it may be warmer in there; therefore it may survive, and we're talking grades here. But, think about what the Mendelians at first said. The Mendelians, at first, said that there was no such things as continua. That it was discreet packets of information called genes that gave you your traits, and these discreet packets were either or. There were no gradations - either or. So it was black or white, not shades. It was long or short, not intermediates. And so there was no genetic basis. There was, from the early work of the Mendelians, there was no genetic basis to explain natural selection.
Well, the good news is by the 1930s this whole field of population genetics rose to the forefront. And so by then, we started to talk, not so much about individuals and variation but pools of genes. So we started by the 1930s to talk about populations, and that my friends is where it starts getting good because here's what starts to happen. Now we're talking about gene pools. We're talking about all of the genes in a population, and now because you have all of the genes, and all of the gene variety you have room now for individual continua to happen within there. And so we're talking about gene pools, and we're talking about collections of individuals. We're talking about a population as a collection of individuals. In fact, what's the definition of a population? The ecological definition of a population is all the members of the same species in a given area. So, we're talking about clumps of organisms together. And now we have the mechanism at this point to consolidate Darwin meeting Mendel. Darwin's continuum and Mendel's discreet units. And so variation at the individual level - variation now we can say happening at the individual level leads to a change in populations. So, we're putting it all together, and so now we have Wolfe's equation revised - Darwin + Mendel + a good working knowledge of population genetics = an A in biology.
Population Genetics and Evolution
The Hardy-Weinberg Theory
Population Genetics: Darwin Meets Mendel Page [2 of 2]

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