Transcript 27. Sex-linked traits

CAN YOU SEE
ALL THE
PRETTY
COLORS??
Are females genetically superior
to males? Let’s find out!!
All of the traits we have discussed this far such
as…
Eye color
Hair color
Dimples
Fire breathing
involve genes located on the autosomes. What are
the autosomes? Let’s find out!
AUTOSOMES= The first 22 pairs of homologous
chromosomes.
All of the chromosomes surrounded by the blue box are autosomes
If a trait is autosomal, the pattern of
inheritance is the same in males and females!
In other words, both males and females have
an equal chance of inheriting the condition.
This isn’t true for all traits. Some traits that
we inherited from our parents are located
on the 23rd pair of chromosomes.
Do you know what name is given to the
23rd pair of chromosomes???
I hope you said they are called the sex chromosomes.
The Sex Chromosomes
Females inherit two “X” chromosomes for their 23rd pair.
Look! Two “X” chromosomes that are the same size
Males, however, have one “X” chromosome and one “Y” chromosome.
Look! A male with an “X” and a “Y” chromosome
Today we will explore why males are
more likely to inherit sex linked conditions.
These sex linked conditions include…
Muscular Dystrophy
Hemophilia
Colorblindness
Let’s take a simple colorblind test!
As you observe the following slides, you are to
determine the letter or number that you see.
Please do not yell out your ideas. Remember
to give everyone a chance.
If you are unable to see the letter or number,
it’s not a big deal. You may simply have the
genetic inability to distinguish that particular
color.
DID YOU
SEE A
25?
DID YOU
SEE A
45?
DID YOU
SEE A
29?
DID YOU
SEE A 6?
DID YOU
SEE A
56?
The individual with normal color vision will see a 5 revealed in the dot pattern.
An individual with Red/Green (the most common) color blindness
will see a 2 revealed in the dots.
An individual who can’t see the big circle at all needs glasses.
So, why are males affected by sex
linked conditions like hemophilia and
color blindness more often than
females???
Females have two “X” chromosomes
Look! Two nice
HOMOLOGOUS
chromosomes!!!
In Order for a female to show a sex linked
recessive condition, she needs two recessive
alleles. One on each chromosome.
B= Normal Vision
b=Color blind
B
B
B
B
Will she be color blind? Why?
I hope you said NO! She has two dominant alleles. As a result, she
has normal vision.
Will this female be color blind?
B
B
b
b
NOPE!!!
This female is known as a CARRIER. She is normal
BUT she carries the recessive allele for the condition.
Will this female be color blind???
b
b
b
b
Yes!!!
How many of the recessive alleles did she need
to inherit in order to be considered color blind?
TWO
So, why are guys more likely to inherit sex
linked recessive conditions?
Look at that
“Y”
chromosome
As we just saw, females inherit two genes
for color vision on the sex chromosomes.
One from mom and one from dad.
How many genes for color vision do
males inherit?
JUST ONE!!!
WHY??
The male “X” chromosome is a normal
sized chromosome just like the two female
“X” chromosomes.
B
B
See. It’s the same size.
The “Y” chromosome is not the same size
as the “X” chromosome. As a result, there
is/are no genes for color blindness or
hemophilia, etc… on the “Y” chromosome.
B
B
LOOK!
NO
GENES
THE “Y” CHROMOSOME
WHY IS
THIS BAD
FOR
MALES????
WILL THIS MALE BE COLOR
BLIND?
B
B
NOPE! WHY?
He has the dominant allele on his “X” chromosome. As
a result he has normal vision.
WILL THIS MALE BE COLOR
BLIND?
b
b
YEP! WHY?
He has the recessive allele. As a result, he is colorblind.
So, Males cannot be
“carriers” of sexlinked disorders.
They either have the
disorder or they are
totally normal.
LET’S TRY
SOME
PROBLEMS!!!