• What’s a “mosaic”?
• Remember the FLUID
– The Plasma Membrane
– P.S. What is a Plasma Membrane?
• An individual (organism, artwork, organelle)
made up of smaller, different ”pieces”…
• So, in a way, WE ARE MOSAICS, too!
• Remember, Females have XX and Males are XY.
– The Y has very few genes - mainly those that contribute to male
characteristics. (Only about 87 genes total.)
– The X much more genetic information – for gender and other
characteristics. (About 2050 genes!)
• Some genes for a disorder/disease are located on
one of the sex chromosomes
• If the gene is linked to the “Y” chromosome,
women will not have the disorder.
– Why? _________________________________
• If the gene is linked to the “X” chromosome, and it
is recessive, women will not express the disorder.
• If the gene on “X” is dominant… both will express
Who is usually affected by
• MEN! Genes for certain traits are on
the X chromosome only…
– Since Men only have one X chromosome
then they are more likely to have the
– Women are somewhat protected since
they have two X chromosomes and are
less likely to inherit receive disorders.
• If women receive a recessive gene on one X
chromosome, they are called “carriers”
because they “carry” the gene but don’t
express the disorder
• Affected males never pass the disease to their
– Men give their “Y” to their sons!
• Affected males pass the defective X
chromosome to all of their daughters, who are
described as carriers
– This means they carry the disease-causing allele
but generally show no symptoms
• Female carriers pass the defective X
– half their sons (affected by the disease)
– half their daughters (who are carriers)
– The other children inherit the normal copy of
How do you solve Sex-linked
• You determine which trait
(or disorder) is dominant or
• Set up a punnett square
using XX for females and
XY for males.
– Assign alleles for X only!
• Solve as usual, keeping in
mind that the Y
chromosome has no allele!
Genotypes: XRXr , XRY
Phenotypes: All offspring
have red eyes.
If Red eyes are dominant and
sex-linked, show the cross
between a homozygous red eyed
female and a white eyed male.
• Hemophilia is a sex-linked trait where XH gives
normal blood clotting and is dominant to the
hemophilia allele Xh
• Identify the genotypes of…
1) a woman with normal blood clotting whose father
2) a normal man whose father had hemophilia.
• What is the probability that a mating between these
two individuals will produce a child, regardless of sex,
that has hemophilia?
Set up the Punnett Square!
- a woman with normal blood clotting whose
father had hemophilia XHXh
- a normal man whose father had hemophilia
What are some X-linked disorders?
• Duchenne muscular dystrophy
• Hunter Syndrome
• Menkes disease(kinky hair syndrome)
• Color blindness
• Inherited diabetes (Type 1)
• A deadly genetic disease that is a result
of fatty acid buildup caused by the enzymes
not functioning properly
• Causes damage to the nerves, resulting in
neurological issues and, later, death
• An abnormal amount of hair growth over the
– Informally called werewolf syndrome, because the
appearance is similar to the mythical werewolf
(Kinky Hair Syndrome)
• Rapid deterioration of the nervous system.
• Weak muscle tone, sagging facial features,
seizures, developmental delay, and
intellectual disability caused by enzymes not
• Children with Menkes syndrome typically
begin to develop symptoms during infancy
and often do not live past age 6
• The “Royal Blood Disease” impairs the body's
ability to make blood clots
– Clots are needed to stop bleeding
• This results in people bleeding longer after an
injury and an increased risk of bleeding inside
joints or the brain
• Tay-Sachs disease is a rare inherited disorder
that progressively destroys nerve cells
(neurons) in the brain and spine
• Enzymes are the culprit AGAIN!
• Paralysis of the nerves cause eventual death
Duchene Muscular Dystrophy
• Duchenne muscular dystrophy (DMD) is a
genetic disorder characterized by progressive
muscle degeneration and weakness
• Until relatively recently, boys with DMD
usually did not survive much beyond their
– Advances in cardiac and respiratory care means
that survival into the early 30s is becoming more
Cystic Fibrosis (CF)
• A genetic disorder that affects mostly the
lungs, but also the pancreas, liver, kidneys,
and intestine Cystic Fibrosis
• The enzymes required to break down mucous
are not functioning, so the mucous collects
• What happens when your immune system
• Albinism is an inherited genetic condition that
reduces the amount of melanin pigment
formed in the skin, hair and/or eyes. Albinism
occurs in all racial and ethnic groups
throughout the world.
– As well as other species!