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