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First experiments of Mendel - Contenido educativo

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Subido el 20 de febrero de 2021 por Andrés G.

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Khan Academy describe experimentos de Gregor Mendel sobre una sola característica de las plantas de guisante.

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Say my mom has blue eyes and my dad has brown eyes. What color would my eyes be? 00:00:00
Now for a long time people thought that the color of my eyes would just be a 00:00:07
mix of the color of my parents. So it would be a mix of blue and brown so some 00:00:13
kind of a dark brownish bluish eyes and that's what they believed for every 00:00:19
single trait. So for example my mom has straight hair and dad has let's say 00:00:24
curly hair then again they believed i would get a mix of them kind of straight kind of curly wavy 00:00:29
hair and so for a long time people thought this is how traits get passed or inherited from parents 00:00:35
to children it'll just be a mix the traits will just be a mix in the children but is this really 00:00:44
how trades gets passed on who's going to answer this question well there was one man actually a 00:00:52
monk named gregor mendel who decided he's going to answer this by growing a lot of pea plants 00:01:00
in his garden now if you're wondering why he chose pea plants then we've talked a lot about this in 00:01:09
a previous video talking about how pea plants have a lot of characters to experiment with 00:01:15
and how these characters have only a couple of traits and all of that so if you need a refresher 00:01:21
it'll be a great idea to go back and watch that video on which is called why Mendel chose pea 00:01:26
plants okay but if you feel you're cool with this then let's go ahead and see what kind of 00:01:33
experiments Mendel performed on these pea plants so Mendel performed a lot of experiments on 00:01:39
different characters right so let me take one example the character height so what he would do 00:01:46
in one of his experiments is he would take a pure tall pea plant and then cross fertilize it 00:01:52
with a pure short pea plant and then see what offsprings they would give now i'm pretty sure 00:01:59
you may be wondering what do you mean by pure plants what does this pure mean pure basically 00:02:06
means if you were to self-pollinate them, so if you were to self-pollinate a tall plant, it should 00:02:11
give all tall plants. If you self-pollinate a short plant, it should give all short plants. And what do 00:02:17
you mean by self-pollination? Well, suppose this is one of the flowers of the tall plant. Now, what I 00:02:23
mean by self-pollination is you take the, what do you call this, pollen grains, yeah, you take the 00:02:30
pollen grains from the flower and put it back into the carpel of the same flower. Basically, you 00:02:36
put it back into the female reproductive part of that same flower and then it'll grow seeds and 00:02:41
then you sow those seeds and then if you find that all the seeds grow into tall plants then that then 00:02:47
we will say this is a pure tall plant this is the meaning of pure and similarly if you were to do 00:02:54
the same thing for the short plant as well so you take one of the flowers of that short plant and 00:03:00
then you self-pollinate meaning you take the pollen grains put it back into the same flower 00:03:05
let it fertilize and then you grow seeds and you sow them and if you find all of them grow into 00:03:09
short plants not a single tall plant but all of them grow into short plants then we will call this 00:03:17
a pure short plant okay so mendel prepared these pure breeds for his experiment a pure tall plant 00:03:22
and a pure short plant let me get rid of these now and so for his experiment you know what he does 00:03:30
he cross pollinates them meaning he takes the pollen grains from one of the plants and he puts 00:03:37
it into the flower of the other and you can take it from anyone to anyone so for example he might 00:03:43
take the pollen grains of flower from the tall plant and then put it into the carpel or the this 00:03:49
part of the short plant so let's say he cross fertilizes them like this and then this will 00:03:55
start growing seeds then he sows that seeds to see what we will get after this cross fertilization 00:04:03
so what do you think we will get well let's get rid of the flowers and make some space 00:04:10
so what do you think we end up with well i would expect to get some medium height plants right 00:04:16
because you have a short one you have a tall you have a tall one you have a short one so maybe they 00:04:24
get mixed and you end up with all medium-sized plants. That's reasonable to think, right? 00:04:29
But to Mendel's surprise and to even my surprise when I learned this, we get all tall plants. 00:04:35
What? That's right. Big shock. 100% of them, 100% of them end up being tall. 00:04:44
this raises many questions what happens to the short one does it have no effect at all 00:04:54
why aren't we getting any medium-sized plants why aren't we getting any short plants what is going 00:05:00
on anyways he addressed these plants as f1 generation plant this is the name that he gives 00:05:05
them and if you are wondering why he called them f1 the word the f stands for a latin word filial 00:05:12
I hope I'm pronouncing that right it means son or daughter okay so that's why this these plants 00:05:21
are called f1 generation first generation sons and daughters of these you can say but yeah 00:05:28
Mendel was shocked by this so he didn't stop over here he started asking questions one of the main 00:05:34
question he was asking is are these plants these tall plants the same as the parent tall plant 00:05:40
are they same they look the same because they have the same height but are they really the same 00:05:47
is this also a pure tall plant that's the question he started asking and to answer that question you 00:05:52
know what he did he did another experiment he didn't stop over here what he does next 00:05:57
what he does next is he takes one of the f1 generation plant which is basically tall 00:06:03
he takes one of the f1 generation plant this is f1 generation oops let me use this white color 00:06:09
So this is F1 generation and he self-pollinates it, self-pollinates it to see what we get. 00:06:17
So again, it'll grow seeds and then he sows that seeds. 00:06:26
What do you think we'll end up with? 00:06:29
Well, surprise, surprise, now some short plants are found. 00:06:32
Another shocking thing to see, right? 00:06:38
Because again, where did these short plants come now from? 00:06:40
Certainly, right? 00:06:43
and guess what Mendel even counted them so in this f2 generation this is the second generation 00:06:44
sons and daughters or offsprings what when he counted them you know what he got he found that 00:06:50
there were roughly three times as much tall as you had compared to short so the tall to short 00:06:57
ratio was three is to one and if you're wondering yes he also cross-pollinated the f1 generation 00:07:06
plants and he gets exactly the same result three to one and you know why this number is so important 00:07:13
because it's not random it turns out he gets the same answer for all the characteristics that he 00:07:20
experiments with i mean for example when he takes when he takes the color of the flower into 00:07:25
consideration again he takes a pure purple colored pea plant and crosses it with a pure white pea 00:07:32
plant in the first generation you know what he gets a similar result this time he gets all all 00:07:39
purple colored flower no yellow no white flowers at all but then when he takes one of these f1 00:07:45
generation purple flower and self-pollinates guess what he gets he now gets uh three times as much 00:07:53
purple as white white comes back it's in minority some small amount three to one ratio but it comes 00:08:02
back with the same ratio, 3 is to 1. So what's going on? Why didn't we see the white flower over 00:08:08
here, but somehow it comes back in the next generation? What is going on? Before we think 00:08:15
of what's really going on, one thing is very sure. Our initial assumption that traits get mixed and 00:08:21
sent to their children is absolutely wrong, isn't it? I mean, if that was the case, we would have 00:08:27
found some medium plants over here. Or over here, we would have found some pinkish colored flower, 00:08:32
mix of purple and white but we don't get that so mendel from his experiments conclusively proved 00:08:37
that traits do not get mixed at all that in itself was a huge discovery but now he had to figure out 00:08:43
what it all meant and i'm going to leave you here hanging with this question as mendel must have 00:08:52
been left hanging with we will look at the exciting conclusion of what all this means 00:08:58
in the future videos. Meanwhile, ponder on this for a while. 00:09:03
See if you can come up with any theory to explain this. 00:09:07
Idioma/s:
en
Autor/es:
Khan Academy India
Subido por:
Andrés G.
Licencia:
Reconocimiento - No comercial - Compartir igual
Visualizaciones:
76
Fecha:
20 de febrero de 2021 - 10:35
Visibilidad:
Público
Enlace Relacionado:
https://www.youtube.com/watch?v=B7VMXUk6TEg
Centro:
IES AGORA
Descripción ampliada:
Historia de la genética. Metodología y resultados de Gregor Mendel.
Duración:
09′ 14″
Relación de aspecto:
1.78:1
Resolución:
640x360 píxeles
Tamaño:
17.78 MBytes

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