Transcript Chapter 5:1
Chapter 5:1
Human Inheritance
Different traits are
determined by a variety of
inheritance patterns
Single Genes with two alleles
Single genes with multiple alleles
Many genes that act together
Patterns of Human Inheritance
We’ve studied traits
controlled by one
single gene with
dominant and
recessive alleles.
ex: widow’s peak
? For you…
The probability that two heterozygous
parents for widow’s peak will have a child
with a straight hairline is _____ percent.
Answer for you
25%
Single Genes with multiple alleles
A gene with three or more alleles for a
single trait has _multiple alleles____
Human blood type has more than two
alleles. How many can you count?
? For you…
Is the following sentence true or false?
Even though a gene has multiple alleles, a
person can carry only two of those alleles.
Answer for you
true
FYI – the gene for tabby
stripes in cats has multiple
alleles
Traits Controlled by Many Genes
When a large number a phenotypes are
possible, usually the trait is controlled by
many genes.
Traits controlled by Many Genes
Traits such as height and skin color
are examples.
The Sex Chromosomes
Determine
weather a
person is male
or female.
Sex Chromosomes
They can carry genes that determine
other traits as well
They are one of the
23 pairs of chromosomes.
Girl or Boy
XX is a girl
XY is a boy
Sex Chromosomes and Fertilization
What happens to the sex chromosomes
when egg and sperm cells form?
All eggs carry one X chromosome. Why?
Half of a male’s sperm cells carry an X
chromosome, while half carry a Y
chromosome.
Sex Chromosomes and Fertilization
Who determines the sex of a baby the
man or the woman?
Duh…the man.
Was it King Henry VIII who killed wives for
not giving him a son? Not too bright!!!
Race to Ellen Egg
? For you…
4. Circle the letter of each sentence that is true
about human sex chromosomes.
a. All eggs carry one X chromosome.
b. Half of a male’s sperm cells have an X
chromosome.
c. None of a male’s sperm cells have a Y
chromosome.
d. The egg determines the sex of the child
Answer for you
4. Circle the letter of each sentence that is true
about human sex chromosomes.
a. All eggs carry one X chromosome.
b. Half of a male’s sperm cells have an X
chromosome.
c. None of a male’s sperm cells have a Y
chromosome.
d. The egg determines the sex of the child
Sex-Linked Genes
Genes on the X or the Y chromosome are sex
linked genes.
An example of this is red-green colorblindness
Let’s read about this…p. 149
Like other genes, sex-linked genes can
have dominant and recessive alleles.
In females, a dominant allele on one X
chromosome will mask a recessive allele
on the other X chromosome. But in males,
there is usually no matching allele on the
Y chromosome to mask the allele on the X
chromosome.
As a result, any allele on the X
chromosome—even a recessive allele—will
produce the trait in a male who inherits it.
Punnett square for color blindness
? For you…
An
example of a sex linked trait
controlled by a recessive allele is
color blindness. This is more
common in men than in women.
Why?
Answer for you…
Because males have only one X
chromosome -- they are XY. Since
color blindness is carried on the X, even
though it’s recessive, males don’t have
anything to mask it.
XcY
Red Green Colorblindness
A girl who receives
only one recessive
allele (written Xc)
for red-green
colorblindness will
not have the trait.
However, a boy
who receives one
recessive allele will
be colorblind.
Carrier – a person who has one recessive
allele for a trait and one dominant allele.
? For you… true or false? A carrier for
colorblindness is colorblind.
Answer for you
False!!!
? For you…
What is the sex
of a person who
is a carrier for
colorblindness?
Answer for you…
The sex of a person who is a
carrier here is:
Female
Another ? for you…
Why is a son who receives the allele for
colorblindness from his mother always
colorblind?
Answer for you…
Why is a son who receives the allele for
colorblindness from his mother always
colorblind?
There is no allele on the Y chromosome
that could mask the recessive allele for
colorblindness on the X chromosome
One more ? For you…
What allele combination would a daughter
need to inherit to be colorblind?
Answer for you
For a woman to be color blind she
would have to have the genotype:
C
C
X X
The Effect of Environment
A. The effects of genes are often altered
by the __environment______.
Environmental Factors
An example of an environmental factor
that can affect a person’s height:
a person’s diet
Mini video on color blindness