# Genetics

Hi. It’s Mr. Andersen and in

this podcast I’m going to talk about this guy, Gregor Mendel, who we credit for really

coming up with the simple ideas behind genetics. He worked in a monastery, grew pea plants,

studied their characters or their characteristics and then he would breed them. Create a bunch

of new pea plants. That’s what each of these seeds in a pea pod is going to be. He would

grow them and then see how those characteristics played out. And he came up with simple, we

call it, Mendelian genetics. Now sadly, nobody really paid attention in his lifetime. And

his work was rediscovered in the early 1900s. But we still give him credit for these ideas.

And so I’m going to assume that you know some basic terms in genetics. And so let me flash

these terms up here. And if there’s some you don’t understand, make sure you take a look

a those. Okay. When I did this in class there were a few stumpers. Some kids were confused

by the difference between a monohybrid and a dihybrid cross. Monohybrid cross would be

something like this. If we’re doing purple pea plants. If I’m crossing that with that.

Since I’m just studying one trait or one gene we call that a monohybrid cross. A dihybrid

cross would look something like this, big P little p big Y little Y. So if I were to

do a cross like this, this would be a dihybrid cross. What’s another one that was confusing?

The independent assortment basically means that two different genes for example, flower

color and whether or not the seeds are wrinkled, those aren’t going to effect each other. In

other words they assort independently and that’s going to take place in meiosis 1 as

the homologous chromosomes separate. And then another term that some people are confused

with is segregation. This is one of his big laws. It basically means that assuming that

it’s a diploid organism, if you are big P little p, there’s a 50% chance that you’re

going to give a sex cell a big P and a 50% it’s going to give it a little p. But most

of the people in class kind of understood the other ones. Ah, here’s another one that

was somewhat confusing. That’s a test cross. Basically if we have something that is big

P little p or big P big P, let’s say this is a purple flower and this is a purple flower,

in other words I know the phenotypes of the two, how do I figure out what the genotypes

are? Well basically if you do a test cross, that means you’re going to cross it with one

that is homozygous recessive. You can imagine if I cross one that’s homozygous recess with

this one, half of them are going to be purple. And if I cross it with this one 100% of them

are going to be purple. And so I can figure out what the genotype of these two are. And

so those are some terms that you probably want to become familiar with before we dig

a little bit deeper into genetics. But before Mendelian genetics, most people believed in

this kind of a blending idea of genetics. That kids look a lot like their parents. And

so there was something inside parents that kind of blended together to make children.

But the didn’t really know what that was. And so the big discovery of Gregor Mendel

was this. He took purple flowers. Now these purple flowers were true breeding. What that

meant is he crossed the purple flowers with themselves over and over and over and over

again. And so what he had was purple flowers. And these ones likewise were white and generation

after generation they only produced white offspring. So we knew that we would call those

pure. Pure true breeding purple and white flowers. He crossed those together. And so

in the parental cross, he crossed purple with white and the F1 generation he basically got

all purple flowers. Now if you think about blended inheritance, this makes sense. If

you take purple paint and mix it with white paint, it totally makes sense that you’re

going to get purple flowers. And so if he would have stopped here, he wouldn’t have

learned anything. But what he did then was took these ones and bred them with themselves

and what he found was this characteristic 3 to 1 purple to white ratio. And this would

be the phenotype ratio. And that white flower had come back. It had skipped a generation

but it was as white as that original white flower. And so that told him that something

was being passed from generation to generation to generation. And the three to one ratio

gave him some hints as to how that was actually passed. If we were to write out how this works,

and this is how he figured it out, well the purple here would be big P big P, homozygous

dominant. The whites are going to be little p little p. And so if you think about if we

cross these two, all of this generation is going to be big P little p. And then if I

cross this with itself, we could do a punnett square but basically one out of four is going

to be big P big P. We’re going to have two of them be big P little p. And then we’re

going to have one of them be little p little p. But since purple is dominant, if you have

one purple that means you’re going to be dominant. That’s why these three right here ended up

being purple. And this one ended up being white. And so that’s pretty much what we had

formulated. And it’s held to this day. So he basically talked about two Mendel’s Laws

or two laws. And basically they are the law of segregation. The Law of Segregation means

that each organism is going to have two genes for each trait. So this one is going to have

a gene for purple and another gene for purple. In this case it’s heterozygous so it’s got

one big P one little p. And so the law of segregation is just like flipping a coin.

Basically what you’re doing is flipping a coin on each of these genes. There’s a 50%

chance that the gamete or the next generation is going to get the big P. And there’s a 50%

chance that it’s going to get the little p. And so the law of segregation isn’t scary.

Basically it means everything is a coin flip. And there’s a coin flip on each gene. Next

thing he discovered was the idea of independent assortment. And so basically once you’ve discovered

genes, the big thing we have to figure out then are genes tied together? In other words,

this one, and please remember these letters because they’ll come up in just a second.

This is a yellow pod. And then this would be a green pod. We’d normally use the capital

letter to represent the dominant trait. In this case it’s yellow. And then the recessive

letter is going to be the green. And then this one would be round seeds and this would

be wrinkled seeds. Or wrinkled pods we could say. And so basically this is going to be

the dominant and this is the recessive. And so what he wanted to study, and this is what

he studied in his traits is, are these two linked? Are they tied together? Or do they

assort independently? And independent assortment basically says that the yellow versus green

is not going to effect the round versus wrinkled. In other words these two genes segregate.

These two genes are separate. Now we’ll find that once we get into a little bit of chromosomal

genetics sometimes they will be linked together. But independent assortment means the genes

don’t effect each other. The yellow versus green and the round versus wrinkled sort independently.

So what do you use to solve these? Well a simple way to do it is just doing simple probability

and using a punnett square. And so if you’re not sure what a punnett square is, basically

let’s say that we have big P little p here. Since we have the law of segregation, half

of the gametes or half of the sex cells are going to get the big P and half are going

to get the little p. We now know that’s called segregation. And so really what the two sides

on the top are going to represent are the different gametes that we have. Likewise,

let’s say we’re copying this with little p little p. Then this is going to segregate

as well. So these are going to be the two different Ps that you can get. And then what

does the middle represent? Well the middle represents fertilization. These are all the

possibilities that you could get when these two alleles that separated come back together

again. And so let’s try some of these kind of in your head. So you could stop if you

want to, but let’s say we take this, purple with white. So if you where to do a punnett

square for that how many different genotypes am I going to get? And the right answer should

be one. Big P little p. And how many physical phenotypes am I going to get? Just one. Let’s

try the next one. Kind of in your head if we do this cross. How many genotypes would

I get? Well I’m going to get three genotypes. Big P big P, big P little p, little p little

p. How many phenotypes am I going to get? Well I’m only going to get two physical phenotypes.

So I’m only going to get purple and white. Let’s try the next one. Let’s say here. How

many different genotypes would I get? Right answer I’m going to get 2 different genotypes.

How many phenotypes? Just one. They’re all going to be yellow. Or this one when I’m mixing

round with round, how many genotypes will I get? 2. How many phenotypes am I going to

get? I’m just going to get one. They’re all going to be round. And so if you’re struggling

with a punnett squares you may want to always, on a monohybrid cross like this, work it out.

When in doubt, work it out. So now let’s go through some sample problems. So I’ll read

it and then quickly come up with an answer and I’ll tell you what the right answer is.

So a coin is flipped four times. Comes up heads each time. What’s the probability the

next coin flip will come up heads? Right answer should be 1 in 2 or half of the time. So basically

what I’m getting at here is all these earlier events aren’t going to effect the next event.

Let’s go a little easier. Classify the following as heterozygous or homozygous. Right answer

should be, this would be homozygous. This would be heterozygous. This would be homozygous.

And this is going to be heterozygous for the first trait, homozygous for the second. We

could get a little more specific. This would be homozygous dominant. This would be homozygous

recessive. This would be heterozygous and sometimes we call that hybrid. Let’s go to

the next one. What is the phenotype of the following? Phenotype remember is physically

what do they look like. I would call this one yellow. This one round. This one green.

And this one’s going to be yellow and round. Let’s go to another one. What’s the probability

of this cross, big R little R, big R little r producing wrinkled seeds? Right answer is

going to be 1/4 or 1 in four probability or 25% chance. And that’s going to be each of

them. It’s a one half probability on each of the little rs. Let’s go to another one.

What’s the probability of these producing green seeds? I would say 1 in 2. These ones

are always going to give the recessive trait. This one’s going to give the recessive trait

half of the time. So it’s going to be a 1 in 2 probability. And now let’s go to the

last one. What’s the probability that this parent and this parent would produce this?

Take a second. See if you could do that one in your head. Okay. If you can’t do it in

your head that fast, you probably don’t know the law of multiplication. And it’s really

simple. Don’t try to do a punnett square. If it’s ever a dihybrid cross the way you

solve it is this. Let’s start on the rs. And so if we have this Rr and this RR what are

the odds that we’re going to produce this Rr? Well if you’re confused you could always

do a little punnett square. So I could write it out like this. Big R, little r crossed

with big R big R. So that’s going to be big R big R, big R big R, big R little r, big

R little r. So the odds that we’re going to produce this, you can see, is a 2 in 4 or

a 1/2 probability. So you just write 1/2 underneath this one. What are the odds with this parent

and that parent that we’re going to produce that? Right answer is going to be, you could

do a punnett square but you should be able to do this one in your head. A 1/2. And since

we have to get both of these. So we have to get this and that then we multiply the two

together. And so the right answer would be 1 in 4. Now if you were to do this as a punnett

square and a dihybrid cross, it’s going to take you minutes and minutes to just set it

up. And you’re probably going to screw up how to do the meiosis. And so always do the

law of multiplication if you have a dihybrid cross. And this goes all the way out to a

trihybrid. All of those are simple, easy to do with multiplication. And I put together

a video on law of multiplication and addition. How it can be applied to genetics. But that’s

Mendelian genetics. In the next video I’m going to talk more about advanced or non-Mendelian

genetics. But for now, I hope that’s helpful.

Thanks

This was great. You clearly know what you're talking about. You really make things clear for me! College genetics test in 2 days!!

Made not make lol

Thank you Bozemannnnnnnnnnnnnnn !!!

Alper + Redouan = True love

true and amazing….. hmmmmmmm….

very helpful. I'm using this to study for my mcat genetic section. I also have genetics class in the fall coming up and I want a leg up on the material

Gosh, I really wish I understood this, lol. Can't wait till I learn this in school. -middle schooler, lol

Best. Teacher. EVER.

thank you so much! 🙂

THANK YOU!!!!! I have been trying to work this out for ages ( I have a really bad lecturer who over complicates things) Now I get it and in time as I have an exam on this tomorrow morning. I didn't realise it was that simple.

now I get it

So if Y and y assort independently and so do R and r. This means that you could still, also, get Yellow Wrinkled pods correct? Seeing as the Y and R are never linked nor are the y and r.

I think in the last problem, the answer should be 1/2 because the probability of getting Yy when you cross Yy x Yy is 1, not 1/2. So you multiply 1/2 * 1 = 1/2.

That last comment is so wrong it must drown in the tears of it's own shame.

Great teacher, he is so patient for student.

amazing way to explain genetics, thumbs up!! and thanks again for your videos.

I have a test tomorrow and I understand this ALOT more now!!! Thank you!!! I will be watching more!!

"and in this PODcast, …"

heh.

thank you sir for this video..this helped me a lot in teaching strategies..

Thank you! You've helped this homeschooler with her biology!!! I couldn't for the life of me understand it in book form XD

you're wrong!!! Gregor Mendel did that exact same thing, only with pea plants!!!!!

thanx … 🙂

THANK YOU

At 4:20 you said "homozygous recessive" when I think you meant "homozygous dominant" but otherwise another great video

Kewl vid,…. does he do this on a samsung tablet + an editor cause it really looks like it..?

please.be.my.bio.teacher

THANK YOU MUCH!!!!'

this is still confusing to me figuring out the phenotypes and the genotypes and the punnett square… my biology teacher has no idea what hes doing but this is a little bit more better then what hes teaching. Thanks for making the vids i really need to learn this on my test !

I love you . you speak well . I really understood all your videos , thank you very very much

this is great !!! explains everything so well !! going to score big on that test now

what is a back cross?

plz answer….

Thank You. This is a great video.

mind successfully expanded, thank you, human

Thank you so much!

Lve it

Thanks so much

Thx

Pi need this for my test

THANK YOU for your videos!

Thank for all your videos! Please keep it up.

Going into an exam today, thanks this helped!! Now hopefully I remember all this

hi neo.

All the words I didn't know was explained by you. Thanks.

i honestly cant understand you

You make it sound so easy.

You have saved me on so many tests

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Help this dog take over youtube by copying and pasting this dog every where

you smart, you loyal, I appreciate you. YOU DA MAN!!!

<3

Every person has the potential to one that was needed at a given point of the earth …

who are interested in Why has been born. science of Human Design (genetica) –

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What is an allele

Legend

3:38 Purple paint + White paint = purple flowers ?

At 5:09, you say that each organism is going to have 2 genes for each trait. Isn't the correct wording 2 alleles for each gene/trait?

Mr. Andersen, if I got a heterozygous genotype (for ex. Pp), would the dominant allele be expressed or carried, or are both alleles going to be carried?

This guy looks like the character Mark watney (Matt Damon) played in "The martian", doesn't he?

Great video btw!

thanks you are greatly appreciated

Informative! This is why i'm doing genetic counselling.

y cant i understand a thing ?????????

I love Genetics (Science/Biology subject) because it helps me learn about people!

In pea plants, yellow seeds

(G) are dominant to green seeds (g). A true-breeding plant with yellow seeds is

crossed to a true-breeding plant with green seeds. The F1 progeny

for this cross are bred with each other. You pick 4 random seeds and plant

them. What is the probability that all the first three seeds produce yellow

plants and they fourth one produces green seeds in that order?

Danny K was here lol

"you see, it makes sense. If you mix purple paint and white paint, it only makes it where you get purple flowers"

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haha get beat

Thanks Mr Andersen!

at 8:21 you didn't even write the answer!! 🙁

I love you man.

Yes it is very helpful. Thank you sir.

Learned more in this video then in the past six weeks from my biology teacher

its so boring

??

you are the best Mr Andersen…..i love your videos

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love this

bio test tomorrow with a teacher that has taught us all nothing , so we all basically self study all the work on our own. I can say for sure this is really helpful.

nice composure

What the heck! I don't still understand anything only 10%…

People are going crazy with genetics and the racial differences!! Traits I look for in a beatch! Intelligence, Health and Beauty! Secondaries are high academic qualifications, knowledge and good morals.

3:49 GSW jokes.. like if you get it

actually, there is a mistake in this video. genes should be aligned or placed alphabetically for example, YyRr should be RrYy since R comes before Y in the alphabet

thx

I know enough to know that organic artificial wombs have already been built. A good amount of knowledge is not readily available to the general public and once the knowledge is known to exist certain things can start to move forward and not doing so can sometime result in some disadvantages and some knowledge can be kept under wraps for decades and i am not even counting the more illegal experimentations.

His camera quality is ass

thank you so much, I love your way of teaching!

2018 still so helpful Mr bozeman

this really helps cause I got a test tomorrow for science

Do the research on the hand lines there is lot of information hidden inside they are genetic

Hand lines are genetic

Dark hand lines person becomes ugly

There should be no lines or light lines on palms

My teacher likes to use you for homework. 🙁

Thank you so much this made Punnett Squares and different assortments in genetics so easy!

pls carry my bio hnrs grade lol

bro thank you my teacher is so assssssssssssss ur like the best

you helped me a loooottt

anyone want to write a 200 word paper on this…..

if i pass my biology test tomorrow, this is the reason why

4th graders: Ha! He got the big pepee!

Me:grow up

great contributor thnx<3 trustworthy source!

AP BIO EXAM MONDAY GANG