Download Ch. 5.1 and 5.2

Human Inheritance and
Human Genetic Disorders
Some human traits are controlled by a single gene
with two alleles, and others by single genes with
multiple alleles.
 Others are controlled by many genes that act
together (polygenetic).
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The Sex Chromosomes are one of the 23 pairs
of chromosomes.
They carry genes that determine whether a
person is a male or a female.
They also carry other traits.
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Sex = are you a Girl or a Boy?
 Girl = XX
 Boy = XY
▪ The Y is much smaller than the X
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These are genes that happen to be on the X
and Y chromosomes. They don’t always have
to do with boys and girls.
Remember, Girls have 2 Xs (XX)
Boys only have 1 (XY)
Genes on the X and Y can be either Dominant
or recessive.
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Colorblindness is controlled by a recessive
allele on the X chromosome (XcXc or XcY)
If you have the Dominant NORMAL gene,
you will see in color. (XCXC or XCY)
If you are a girl and have one of each (XCXc)
then you are a carrier. You CARRY the gene
for colorblindness, but you see in color!
 Because C is NORMAL color gene.
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WHY?!
Because they only have 1 X (XY) so therefor
they don’t have the option of a back up gene!
Girls do! (XCXc)
If you have a backup gene, you are a carrier!
So, why do boys have colorblindness more
often? (you answer!)
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Even if your genes say you are to be VERY
TALL, you might end up short if you don’t eat
right!
It’s like trying to plant a giant pumpkin seed
in the dark and never watering it! IT WON’T
GROW!
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1. What causes Red/Green color blindness?
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2. Why is it more common in males?
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3. Are a person’s characteristics determined
only by genes?
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4. What is the genotype for Female?
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5. What is the genotype for Male?
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A Genetic Disorder is something PASSED
DOWN through the generations.
IT CANNOT BE “Caught” (Diseases are
“caught”)
It just means that you have a different trait
that makes some things in life more difficult,
but most of the time, you can still function
like everyone else.
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Some are caused by mutations in the DNA.
Others have to do with the number of
chromosomes you get. (Remember, you are
supposed to have 23 from MOM and 23 from
DAD)
If you don’t get enough, or you get too many,
disorders happen.
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Cause: Recessive allele on one chromosome
Effect: thick mucus that leads to difficulty
breathing and can lead to death.
Cause: A Co-dominant
gene (yellow plus blue =
green)
 Effect: The sickle-shape of
the blood cell makes it
difficult to transport
oxygen to the body. It is
usually very painful!
 SS = Full sickle-cell
 SB = half sickle-cell, half
normal blood cells
 BB = Normal blood cells
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Cause: A recessive
allele on the X
chromosome
 Effect: uncontrollable
bleeding. The blood
does not clot well, and
it can lead to death.
 Question: Do boys and
girls get this equally?
Why or why not?
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Cause: An EXTRA #21 Chromosome. (could
be from MOM or DAD)
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Use a Pedigree to track down your genetics
from one generation to the next!
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Karyotypes are used to detect Chromosomal
Disorders:
Q1: Is this
a girl or a
boy?
Q2: What
genetic
disorder
does this
child have?