Genetic Inheritance 1
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Genetic Inheritance 1

Hi there and welcome to a video
outlining genetic inheritance. So genetic inheritance is a way that we use to track the
way traits are passed from individuals through the generations through families.
So we can use kind of a fairly simple letter system, although we’re finding out
it’s a lot more complex than that. But we can at least use that to kind of have a
starting point so we can track the movement of these genes and how it’s
inherited over time. So the genotype refers to the actual genes that are
inherited. And just a reminder with genes those are if you have your chromosome
here….that is a segment of the chromosome where a particular set of adenines,
guanines, cytosines and thymines or A’s, T’s, C’s and G’s are found. So the A’s, T’s, C’s and G’s
are throughout the chromosome itself but we can find specific sequences that are
actually meaningful. So if we were to start for example like say in the middle
here and go somewhere else that may not code for anything but if we started a
very specific start point in a very specific end point, that will actually
make a protein that is then translated into some sort of expressed trait which
I’ll get into in a moment. And so that part is called a gene and we’ve had to
do sequencing and then track that to see what right right ATC and G combination
leads to a specific gene expression or a gene that we can see. So genes that are
inherited so typically we use a letter system and I’m just going to use kind of
an artificial system here so we have remember you get a gene from your mother’s side and a gene from your father’s side. So your sets of chromosomes half comes
from the mother’s side half comes from the father’s side we’re not going to worry
about crossing over anything like that right now. And so we just use simple
letters we don’t want to right out the whole A, T, C and G combination
because that’s thousands of bases long. The A’s, T’s, C’s and G’s would be many many. So we just use letters as a shorthand method to track which gene that is and
what it means. So that’s the letter part. Now the phenotype part are the physical
traits. And so what you need to do when you’re kind of tracking these problems
to outline this… whoops…physical traits… what we need to do there is to make sure
that we align each letter with an actual trait. So we could say that the capital G
is prefers green-chili. So…I’m living in New Mexico that is a
very big deal here what you prefer for most people and then the small G would
be prefers red chile. Again and this is kind of an artificial system I’m making
up here. Most inheritance patterns are very complex but we do start with this
kind of beginning overview to see that first step in how things are passed
through the generations and then the fact is there’s usually other genes that
come into play that control the expression we’re not going to get into
that level of detail. But just to have something to start with to track the traits. And the allele refers to different forms of a gene. So for this particular example here, the
gene I would say codes for chile preference..we’re not saying “what”. It just
codes for chile preference. The allele types are red or green. Now if there are
other chile types you wanted to put in there you could have other alleles so
but we’re just going to stick with red or green here. And then you have what’s
called a dominant allele so this is the allele that sort of overrides the
expression of the other. And it’s typically specified by a capital letter. And recessive is typically specified by
a lowercase. So in this example here it would be the G, the lower g, lowercase G.
So what you’re saying is if you have an individual that has an upper and
lowercase, so they have a green chile and a red chile allele type. The physical
outward trait that you’re going to see is going to be a green chile preference
in this particular example. So what we can do is we can set up Punnett squares.
And Punnett squares can track the likelihood that certain traits will be
passed down. So this is kind of a fun example here that we’re using. But if we
were looking at a disease….uh disease allele for example, it would be extremely
important to predict the likelihood that that would be passed down to the next
generation. You would need to know if that’s a dominant or a recessive allele
as well. So I could take….let’s say I’m going to use the symbol here, the mother
sign and I’m gonna make her what’s called heterozygous. So that’s
another term we can define. So they have one of each allele type or
maybe we could say two different alleles. The other possibility is homozygous. Now
keep in mind there some traits that can have more than two alleles so we don’t
want to say it’s gonna contain all of those but it would have two different
alleles. Homozygous has just one allele type they still have two of them but
only one type. So an example I could use here would be the the red chile
phenotype which would be little g- little g. Or the green chile phenotype which
would be capital G-capital G. And then in this case it would be for heterozygous..this one here. So that would be the possibilities that can be passed on into her ovum. That will go into the zygote that’s there. So
we’ll pick for the father…we’ll pick that he’s gonna have a red chile
preference. And so he’s going to be homozygous… combine those together. So what you do, oh I forgot this part, …a little symbol just to remind us it’s the
father’s type. We do that to just again just kind of bookkeeping to track which
parent we’re talking about. So remember the fathers making sperm, the female is
making ova. And so those are the two different possibilities she can make.
When you make the gametes this egg or the sperm, those those cells only get one
of each type because we have the amount of genetic information so that when the
zygote is formed when fertilization occurs you still get back up to the
normal amount. So possibilities would be for offspring
and we typically just write the capital letter first. It’s not critical, but if
you kind of keep that same system it’s just visually a little bit easier to see
where your same sets are. So this one would make a heterozygote; homozygote;
heterozygote; homozygote. So what we would say is there’s 50% or 1/2 are GG.
And this is where it really helps to have a nice key because a lot of times
you get here and you’ll think…..”wait, what does that mean again?” So you can go back up. These are the red chile preferers , And then 50% are heterozygous. And they are in this case, Gg. And those prefer green chile.
Keep in mind the homozygous dominant combination would have given you that
same phenotype as well we just didn’t have that possibility this showed up
here. So that’s basically it. Probably the. biggest challenge with these
problems is really just that sort of keeping track and keeping organized. So,
having a clearly defined letter system and then defining what they mean because
once you get that it’s fairly easy to set that up and do the box and get the
ratios. But sometimes you’ll get these great setups in here and then you forget
what the letters mean so that’s where a good key helps you there as well. Okay
that’s all I have for Punnett squares. They can get a lot more complex with
alleles for other traits as well so this is just the very simple kind of starting
on a square to work with getting you set that up. Thank you very much! This is
Corrie Andries for CNM!

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