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Warm Up #6
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2/08
What happens to the chromosome # in mitosis?
What happens to the chromosome # in meiosis?
What is the abbreviation for the steps in mitosis?
What’s the abbreviation for the steps in meiosis?
Draw a picture showing difference between mitosis &
meiosis during metaphase (use 6 chromosomes)
Agenda
2/08
• Sex-linked trait notes
• Group practice (w/cards)
• Card share-out (bonus points)
Learning Target
• I can describe and explain the differences
between codominant, incomplete
dominant, polygenic, and sex-linked traits
CH 11 Notes #6 Sex-linked Traits
2 Ways to reproduce
1. Sexual: sperm and egg make offspring
Examples: dogs mating to make puppies,
male flower pollinates a female flower
**Advantage: shuffles genes to keep populations
healthy**
2. Asexual: one individual clones itself
Examples: bacteria divide to reproduce,
a new tree grows from a stump
Fish fertilizing eggs
Degusia
(animal)
cloning it’s
own head
Snakes
mating
Plant
cloning
itself
How do you become a boy or girl?
First 22 pairs of chromosomes are called autosomes
Sex is determined by the 23rd pair of chromosomes
(Called “X” and “Y”)
Females: XX
Males: XY
Question
• Does the mother or father determine the
sex of the baby? Or both?
 The father’s sperm
determines sex of the
baby
 He gives an X or Y to
the gametes.
 The mother only gives
an X to the gamete
What are the % chances of
having a boy or girl?
• Chances of having either sex:
always 50%
Check for Understanding
• A couple are having a baby, what are the chances
the baby will be a girl?
50%
• A couple have had 3 girls, what are the chances
their next child will be a girl?
50%
• A couple have had 13 girls. What are their chances
their next child will be a girl?
50%
Sex-linked genes are genes found on
a sex chromosome
• Examples:
XrXR
XrY
Sex-linked Genes
• Sex-linked recessive traits will show up more
often in males because they only have 1 X
chromosome
XR = normal
Female
• XRXR = Normal
• XRXr = Normal
• XrXr = Disease
Xr = disease
Male
• XRY = Normal
• XrY = Disease
Carriers
= Fem
• Carrier: A female who has an allele for a
genetic disease but does not show the
disease.
– Carrier genotype: XRXr
• Males cannot be carriers because having
1 allele for the disease gives them the
disease.
– XrY = diseased
Examples of sex-linked traits in
humans:
1. Color Blindness
2. Hemophilia
3. Muscular Dystrophy
4. Male pattern baldness
5. Sickle cell anemia
Colorblindness
• Cannot tell the
difference between
red and green colors:
• People with red-green
color blindness see
either a three or
nothing at all.
• Those with normal
color vision see an 8.
Colorblindness
• A person with normal color vision sees a number seven in
the circle above.
• Those who are color blind usually do not see any number
at all.
A female carrier (XNXn) and a man with normal
vision (XNY) have kids. What are the chances their
kids are colorblind?
XN
Normal vision is dominant (N)
XN
Colorblind is recessive (n)
Girls _______%
Boys_______%
Xn
Y
Hemophilia
Hemophilia- Lacking in the
ability to clot blood
– There is a gene on the “X”
chromosome that control
blood clotting
– People who have
hemophilia are missing the
protein to clot blood
– They can bleed to death by
minor cut.
A female carrier (XHXh) and a man with hemophilia
(XhY) have kids. What percentage of their kids
have hemophilia?
Xh
Normal clotting is dominant (H)
XH
Hemophilia is recessive (h)
Girls _______%
Boys_______%
Xh
Y
Muscular Dystrophy
- Results in
weakening/
loss of
muscles
- Caused by
defective
version of
gene that
codes for
muscle
Here’s the results
• For girls: 0% have the
trait
• For boys 50% have it.
• Percentage is higher
for boys because
whatever X they get
determines the trait,
for girls they have to
get 2 recessive X’s.
M
X
m
X
M
X
M
M
X X
M
m
X X
Y
M
X Y
m
X Y
Video
• http://www.youtube.com/watch?v=H1HaR
47Dqfw
Group practice
• Get with other people with card number
• Different suits have different jobs
• Last 5 min: Randomly calling to give answers!
Leader: Keeps the group on task
Time Keeper: Keeps track of time, keeps things
moving
Note Checker: Makes sure all members
are using their notes on the problems