How many chromosomes do
humans have?
Humans have 46 chromosomes.
They occur in 23 pairs!
Do you remember
what this is called?
A karyotype
Pair 1 – 22 are known as
autosomes.
The 23rd pair are called sex
chromosomes.
• X Chromosome
• Y Chromosome
Do you remember what
combination codes for
female and male?
– XX – Female
– XY – Male
Sex Linked Genes
• Some genes are located on the X chromosome.
• These traits are called sex-linked traits and are
controlled by the genes on the x chromosome.
• Females receive two alleles for these genes, but
males only receive one, since they only get one X
along with the Y.
– Because XX = Female and XY = Male
• Examples include color blindness, pattern baldness
and hemophilia.
• Females who are
heterozygous for a trait
are known as carriers
– A female can be
• XBXB – normal
• XBXb –carrier
• XbXb - colorblind
• Males CANNOT be
carriers because they
only have one X
chromosome
– A male can be
• XBY – Normal
• XbY - colorblind
This PS shows a cross between a normal
man and a woman who is a carrier.
(Notice that NO allele is attached to the Y!)
Sex-linked Problem…
• A woman has normal color vision and is married
to a man with normal color vision. One of their
two sons has normal color vision but the other
son is colorblind. How was this possible?
• First, figure out the genotypes of the parents.
Mom = XBXb because she has to be carrier
Dad = XBY because we know he is normal
• Will any of their daughters be colorblind? Will
any of their daughters be carriers?
• Do the Punnett square to find out!!
A pedigree is used to show genetic
inheritance within a family
• Squares represent
Males
• Circles represent
Females
• Horizontal lines show
marriages
• Vertical lines show
offspring
• So, let’s analyze this
pedigree!
• A pedigree is a graphic representation of genetic
inheritance.
• In most instances, the shapes are either shaded or not.
• If the shape is shaded, then the individual has the
particular trait.
Celebration of
Learning Moment! 
Pedigree Problem Worksheet
Occasionally, problems occur at
the chromosomal level.
We call these problems genetic
disorders
• A genetic disorder is a disease that is caused
by an abnormality in an individual's DNA.
• Abnormalities can range from a small
mutation in a single gene to the addition or
subtraction of an entire chromosome or set of
chromosomes.
• There are various genetic disorders, some
dominant, recessive, sex-linked, co-dominant.
We’ll discuss the more frequently
encountered genetic problems human have.
WARNING:
Some images may be explicit or hard to
see.
Use your knowledge of these disorders
to be kind and compassionate to
others!
Dominant Allele Disorders
• What does it mean
by dominant?
Examples:
1. Achondroplasia
• Dominant
dominates over the
recessive allele.
• DD or Dd
1. Huntington's Disease
Achondroplasia
• Long bones do not develop
properly
• Results in unusually short arms and
legs, a large head and relatively
long torso
• Only 1/8th of the children born with
this condition inherited it from a
parent.
• Most cases of achondroplasia
occur spontaneously and are the
result of a new mutation in an egg
or sperm of one of the normalappearing parents.
Huntington's Disease
• Progressive, degenerative
disease
• Causes certain nerve cells
in your brain to waste away
• Results in uncontrolled
movements, emotional
disturbances and mental
deterioration.
• Huntington's disease is
inherited as a dominant
allele so if one parent has
this disease, the offspring
have a 50% chance of
inheriting it.
Recessive Allele Disorders
• What does it mean to
be recessive?
– Dominated by
dominant allele
• What HAS to be
present to have a
recessive phenotype?
– BOTH recessive
alleles
Examples:
1. Cystic Fibrosis
1. Tay – Sachs Disease
1. Albinism
Cystic Fibrosis
• Inherited recessive disorder
resulting from a mutation of the
gene that regulates the
secretory glands, including
mucus and sweat glands.
• The characteristics of cystic
fibrosis are salty tasting skin,
normal appetite but poor growth
and poor weight gain, excess
mucus production, frequent
chest infections and
coughing/shortness of breath.
• Both parents must carry the
allele for the child to inherit the
condition.
Tay-Sachs Disease
•
•
•
•
•
Fatal genetic lipid storage disorder
in which harmful quantities of a
fatty substance build up in tissues
and nerve cells in the brain.
Infants with Tay-Sachs disease
appear to develop normally for the
first few months but as fatty
material builds up, a relentless
deterioration of mental and
physical abilities occurs.
The child becomes blind, deaf,
and unable to swallow. Muscles
atrophy and they can no longer
swallow.
Children with Tay-Sachs disease
usually die by age 4.
Both parents must carry the allele
for a child to inherit the condition
Albinism
• Recessive disorder that occurs
when one of several genetic
defects makes the body unable
to produce or distribute
melanin, a natural substance
that gives color to your hair,
skin, and iris of the eye.
•
•
In one type of albinism, people
have white or pink hair, skin, and
iris color, as well as vision
problems.
Another type of albinism, called
ocular albinism type 1 affects only
the eyes. The person's skin and
eye colors are usually in the
normal range. However, an eye
exam will show that there is no
coloring in the back of the eye .
Can you remember any of the genetic
disorders we’ve previously discussed?
• Klinefelter’s Syndrome: Males with one extra X
chromosome (XXY)
• Turner Syndrome: Female disorder where girl
only has only fully functional X chromosome
• Down Syndrome: Trisomy of the 21
chromosome
• Sickle Cell Anemia: Misshaped red blood cells
Create an informative poster!
1. You and your partner will
pick a genetic disorder
and research it
2. Create a detailed AND
creative poster to inform
others about your
chosen disorder.
3. This is the ONLY time
you will be allowed to
use your device. And,
you should ONLY be
researching!!!