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Biology: Mendel: Segregation, Recombination


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About this Lesson

  • Type: Video Tutorial
  • Length: 7:49
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 85 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: Mendelian Genetics and Mutation (36 lessons, $54.45)
Biology: Gregor Mendel (4 lessons, $6.93)

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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Let's take a quick look at what Mendel has through his f[1]. What Mendel has through his f[1] is he's got these smooth plants--and I'm using the smooth and wrinkled because it was his first experiment. We're not going to go through all of his experiments. One just sets it out so nicely. Smooth and wrinkled. We've determined to use a certain criteria to describe these. Remember Mendel's law. Mendel's law of segregation said, "You get one of your traits from each of your parents." Which means since you have two parents, or certainly a sperm and an egg, then you're going to get a gene for this trait from each of them. So, we decided, okay, since the smooth was the one that Mendel noted was the dominant one, we decided to call S smooth and to show that that was what masked wrinkled, instead of calling wrinkled W, we're calling wrinkled s, for wrinkled.
This worked like a charm, because if we decide to call this P generation here and we say that this is pure breeding--that's so important, SS and this was pure breeding--had to be ss. It was so clearly delineated that in the f[1] generation we would get nothing--if you look at the sperm that this one will produce and the eggs that this one will produce, or if this were the female the eggs that this one would produce and the sperm that this one would produce, you have no choices. You have no choices. This is always going to produce S. This is always going to produce s and so your f[1] is going to be Ss. That's where we are now. But remember, we have to describe--we have to figure something out. He got smooth and wrinkled in his f[2].
Now, I have to introduce some words to you. We in genetics have a vocabulary, just like we do in every other field, where I have to talk about things. So, I'm going to go back to this thing and I am going to say that you're going to see this described several different ways. Okay. First of all, this pure bred line, we use the term homozygous to define that, same zygous. So anything that has the two alleles the same is going to be called homozygous. In my f[1] we're going to talk about the fact that this is a hybrid--is the term we use all the time. Well, there's another way, in terms of its zygosity to describe this other than hybrid, which is cool, you can use the word hybrid, but we also refer to that as heterozygous or mixed. Just some vocabulary, because now I can talk to you about heterozygous and you know I'm going to be talking mixed. So, now I don't have say, "They were pure breeding lines." I can say, "Hey, they were homozygous" and you know exactly what I'm talking about. So, it's like having our own little secret code language.
So, homozygous gave us heterozygous and now here's what he did. Remember in his law of segregation he said that these are going to separate. So, let's go that heterozygous f[1] and let's cross them. But now, we're going to have segregation here. Remember this. Now it gets a little more interesting. So, let's take a look--let's make this the male and let's take a look at the gametes this male can form. You can only send one per sperm and therefore, according to Mendel's law of segregation, half of the sperm will have the S, the smooth and half of the sperm will have the s. Okay? Similarly the female portion of the flower can do the same thing. We're going to have segregation of these alternate alleles. Half of her eggs can have a S and half of her eggs can have s.
Now we come to why the science of statistics and probability was a rainbow for Mendel and why it opened his eyes. Because he saw what was happening here. He saw that when you sprinkled sperm on an egg, in these flowers, that it was merely probability that the odds were that some of the S's were going to land on some of the S eggs. Some of those S's would land on some of those s eggs. Let's just look at those combinations. This would give me a SS. Right? This would give me a Ss. But remember, Mendel was no dummy, he realized that, wow, we have other sperms. Half the sperms I'm sprinkling over this stigma have a s and so therefore this s might fertilize these those S eggs too. Possibility is it might.
Wow, look at that. Ss, but that's not all, because there is still a fourth combination, ss. Let's take a look at this in relation to his law of segregation. Quick reminder, S equals smooth, s equals wrinkled. Let's look at what's going to happen due to the recombination of these different genes. Well, we have SS, about of the possibilities are SS, are Ss and the other is sS, which if you look at it--remember smooth is dominant, these two are literally the same. In fact, we're going to write them both as Ss as we get to convention. Last but not least, we come to this one and I'm going to put this over to the side here, because that's interesting, ss. One, two, three, four possible combinations.
I'm going to lay another word on you. The genotype or the type of gene present versus the physical expression of those genes, physical expression. Why am I going phy, like that? Am I a fool? No. The word phenotype begins with ph, phenotype, p-h-e-n-o, phenotype and so does the word physical. So, you'll always remember now, because of this guy phy-ing at you, that the phenotype always describes the physical expression. This genotype, SS is smooth. This genotype, Ss, smooth dominates, smooth. This genotype, sS, smooth dominates, smooth. But the wrinkled pops out in of the cases. Phenotype wrinkled, smooth, wrinkled. The law of segregation explains how traits can be inherited.
Mendelian Genetics and Mutation
Gregor Mendel
Mendel's Conclusions: Segregation and Recombination Page [2 of 2]

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