Mendel's Law of Segregation

previously we discussed a very important experiment that was conducted by Gregor Mendel which basically gave rise to the law of dominance the principle of dominance so let's briefly recall what this experiment was let's summarize this experiment so what Gregor mendle did was he crossed a true breeding tall plant with a true breeding short plant and every time he tried this experiment he always saw that the F1 generation offspring was always tall in fact every time he tried the experiment with other traits he got the same exact result he saw that the F1 generation Offspring always resembled one of the parents and never the other parent now because of this result he posed he asked the following question what exactly happens to the trait for shortness for the short height within this offspring does this F one generation Offspring lose the trade that gives it the shortness quality well to answer that question what he did was he took the F1 generation Offspring and he made it it with itself to produce the F2 Generation Offspring and what he saw was that although about 75% of the F2 offspring were in fact tall the remaining 25 were actually short and that meant that this tall F1 generation Offspring had that short trade in it all along but it was being inhibited it wasn't actually being expressed so because of that what he proposed was that each one of these plants contain two hereditary factors that code for that given trait in this case for that given height and nowadays we know that these two hereditary factors are simply the genes found on homologous chromosomes and we'll see exactly what that means in just a moment so basically he argued that because this tall F1 generation Offspring contains that short trade but the short trade is not being expressed that means the tall trade is actually dominant over that short trade which is set to be recessive so to see what we mean let's take a look at the following diagram so this is the tall true breeding plant and what that means is it contains two genes that are both essentially tall so we have uppercase te so we have uppercase dark purple tea and uppercase light purple tea now in this case we have a short plant that is true breing which means both of these genes are lowercase te and that means they're short they're recessive and so let's suppose we have a red color and we have the orange color for the second lowercase te now this is called the law of dominance what he proposed next was the principle of segregation also became known as the law of segregation or Mendel's law of segregation now what he argued was that whenever the gamits are formed before we actually have the mating process take place the two genes that code for that same trait in this case the height behave like particles and actually separate during the process of gam formation so to see what we mean let's take a look at the following diagram so before they can combine to actually form The Offspring both of these must actually segregate they must separate into different compartments into different cells for this particular case we have the dark purple T go into its own cell and a light purple T also go into its own cell and so let's suppose this is the male parent so this is the male gamits the same thing happens here let's say this is the female parent so they they separate they segregate into these individual compartments individual cells let's call these the female gamits and notice that this means that the Gams our sex cells these sex cells right here are formed and only only contain one copy of the pair of genes so this is the pair of genes but each one of these cets contain a single copy of that pair of genes and notice we actually have no mixing between the genes these genes are separate entities and they separate into these different compartments and this separation process that takes place when we actually form the gamt is known as law of segregation so this idea that the two hereditary factors our genes for any given trait in this case our height segregate from one another during G formation became known as Mendel's law of segregation now the amazing thing about this discovery was this was basically discovered at the time when we knew nothing about myosis or mitosis so even though at the time when mendal made the discovery we knew what gamuts were and we knew that gamuts must fertilize to form the zygote we knew nothing about how meiosis takes place and so we knew nothing about how the gamuts are actually formed so although this was actually correct it wasn't exactly correct because we knew nothing about meiosis so now let's actually try to combine the concept of meiosis with the principle of segregation so basically nowadays we know that segregation is a direct result of the separation of the homologous chromosomes that contain the two genes those two hereditary factors which uh which takes place during the process of meiosis so let's basically tweak this slightly to see how it actually takes place so let's suppose we have parent number one this is parent number one and this is parent number two so so what exactly does the cell look like inside the toll parent the true breeding parent number one so basically we have a pair of homologous chromosomes chromosome number one is homologous to chromosome number two and what that means is the genes found on this chromosomes are basically homologous they code for that same trait that are found on this so if this chromosome carries let's say the dark purple uppercase te then this one homologus to it carries the uppercase light purple te now during uh during the process of meiosis we have replication taking place and each one of these are replicated to produce cyto chromatids here and cyto chromatids here so these two are identical these two are identical but these are homologous with respect to one another next meosis one takes place and when meiosis one takes place these are basically pulled to opposite sides to form the two different cells and we form the following cells and when meiosis 2 takes place then these are separated these cyto chromatids are separated and we form the following four gametes of parent one and the same exact thing takes place with parent number two except here we have these two homologous chromosomes that contain genes that code for the short trade so we have the lowercase red tea and the lowercase uh orange tea and so we have replication taking place to form these two pairs that now consist of identical cyto chromatids then these separate to opposite sides then these separate to form the following four uh gamuts and now that we form these two gamuts let's Imagine This is the male this is the female one of the male has to combine with one of the female to basically form that final product that final Offspring the F1 generation so let's suppose that the uppercase te that is light purple mixes with the lowercase T that is red so we have the mixing process take place and we form the following zode that eventually gives rise to this F1 generation offspring and so we have uppercase t lower case T we basically have the following third case and since the toll trade is dominant over that short trade we have the fact that no matter which one of these possibilities we actually obtain we always get the same exact result because uppercase t is dominant over lowercase T we get the fact that this will always resemble this parent and never this par so notice in this particular example this T could have mixed with this T to produce possibility one or this T could have Mi could have mixed with this T to produce possibility two or this could have mixed with this to produce possibility three which we got in this case or this T could have mixed with this to produce possibility four and we have the same exact proportions the same exact possibilities when these are mixed so basically this is what we call the law of segregation and it takes place as a result of meiosis so during the process of meiosis those homologous chromosomes that contain the genes that code for any given trade basically separate from one another into their identical compartments into their identical gamuts into their identical cells and this is what we know as the princip all the law of segregation

Channel: Andrey K

Views: 169,468

Keywords: law of segregation, principle of segregation, Mendels prinicple of segregation, Mendels law of segregation, law of segregation and meiosis, segregation in meiosis, true breeding plants, law of dominance, dominance and segregation, Mendelian segregation, what is law of segregation, meiosis and law of segregation

Id: FG3S2qxy8GE

Length: 10min 36sec (636 seconds)

Published: Sat Dec 20 2014