Transcript PowerPoint Presentation - Elmwood Park Public Schools

WHAT IS A GENE??
A GENE is found on a chromosome.
It is a sequence of DNA that “codes” for a trait. That means it
holds the information for something about us, like eye color,
or skin tone, or height, or how to make bone.
What are some
things that our
genes might code
for?
WHAT IS AN ALLELE?
An ALLELE is the part of the gene that holds the
actual trait. There are TWO alleles for every gene.
You get one from your mom and the other from
your dad.
Traits can be either DOMINANT or RECESSIVE.
Depending on which ones you get from your parents will determine
which ones you see.
Your GENOTYPE tells you what genes you have.
Capital letters represent DOMINANT, and lower-case letters
represent RECESSIVE.
Being you get one from mom and one from dad, you have 2 letters
for each trait. They can look like this:
BB
Bb
bb
In the first one, you got a dominant trait from both parents, in the
second one, you got a dominant trait from one parent and a recessive
trait from the other, and in the third, you got a recessive trait from
both parents.
Now let’s say that Black hair is dominant to Blonde hair.
So Black is “B” and blonde is “b”.
If you have “BB” that means you got Black hair from
both your parents, so your hair is Black.
If you have “Bb” that means you got Black hair from
one parent, and Blonde from another. Because Black is
dominant to Blonde, your hair is Black.
If you have “bb” that means you got Blonde hair from
both your parents, so your hair is blonde.
PHENOTYPE is what you see. So your phenotype is
either Black hair or blonde hair.
BB
Bb
bb
So our Genotype determines our Phenotype.
What genes we get from our parents
determine what we look like. But what
decides which genes we get?
Unfortunately, it is completely random, but
we can predict the odds of a single trait by
doing something called a “Punnett Square”.
BB
Bb
If these two people were to have a child, what would it look like? Let’s find out!
How do we do it?
We start by making a Punnett Square,
which is like a multiplication table. We put
the letters from one parent along the top,
the letters from the other parent on the
side, and multiply. We do this because the
child can only take ONE from each parent.
What’s the percent phenotype for this
child? What about the percent genotype?
B B
B BB BB
b Bb Bb
Bb
Bb
If these two people were to have a child, what would it look like? Let’s find out!
What are the phenotypes these parents can
have?
What’s the percent phenotype for this
child? What about the percent genotype?
B b
B BB Bb
b Bb bb
Different genotypes have different names.
BB is called HOMOZYGOUS DOMINANT
Bb is called HETEROZYGOUS
bb is called HOMOZYGOUS RECESSIVE
BB
Bb
bb
BBAA
BBaa
bbAA
bbaa
Sometimes, we have more than two phenotypes
for a trait, like hair color. We can have black,
blonde, brown, or red. This means that more
than one gene controls this trait.
This means our Punnett Square is going to be
bigger.
BbAa
BbAa
BA
What if these to parents had a kid?
They can only give ONE allele from
every gene (pair), so if they have
TWO pairs for hair color, they are
going to give TWO alleles. Let’s see
what the Punnett Square would
look like.
Ba
bA
ba
BA
BBAA BBAa BbAA BbAa
Ba
BBAa
bA
BbAA BbAa bbAA bbAa
ba
BbAa
BBaa BbAa Bbaa
Bbaa
bbAa
bbaa
BBaa
BBAA
bbAA
bbaa
So which phenotype will we see? Remember,
homozygous dominant and heterozygous
genotypes will give you the same phenotype!
BA
Ba
bA
ba
BA
BBAA BBAa BbAA BbAa
Ba
BBAa
bA
BbAA BbAa bbAA bbAa
ba
BbAa
BBaa BbAa Bbaa
Bbaa
bbAa
bbaa
WHERE DID WE DISCOVER THIS??
Gregor Mendel was a monk who
experimented with pea plants.
He found that if you took certain
peas with certain traits, like
color or texture, and crossed
them to make new peas, you
could predict the odds of the
traits of the next generation of
peas. This was the basis for
Punnett Squares, and genetics.
EXCEPTIONS TO THE RULE
CODOMINANCE
When neither trait is
dominant, so you see BOTH
expressed in the phenotype
INCOMPLETE DOMINANCE
When one trait is not completely
dominant over the other, so you
see a blend of both traits
WHAT ABOUT MUTATIONS?
Mutations occur when there
is an error in DNA
replication.
The mutation becomes a
part of the person’s
genetics, and CAN be
passed on to children!
Some mutations can be seen.
However, some mutations cannot!