Download X chromosome - Fort Bend ISD

Sex-Linked Traits and
Karyotypes
Pre AP
Hemophilia
Read the passage about hemophilia in dogs
 Answer the following questions in your Bell
Ringer journal

– Do sex-linked disorders happen in humans only?
– Is it important to know if a trait is sex-linked or not?
Why or why not?
– Does it surprise you to find that there are similar
genetic disorders in dogs as humans? Explain.
There are traits that are controlled by one
gene with 2 alleles. Often, one is
dominant and the other is recessive
 Example:
widow’s peaks and dimples.

Some traits are controlled by a gene with
multiple alleles – 3 or more for a single
trait.
For example: blood types and skin color in
humans.
There are 44 chromosomes that we call
autosomal chromosomes.
 However, there are 2 chromosomes that
determine our sex and we call them sex
chromosomes.
 These 46 chromosomes all carrier genes
on them that determine our traits.

Out of our 23 pairs of chromosomes, 1
pair is the sex chromosomes (X and Y).

Female = XX

Male = XY

Each egg produced by an ovary contains one X
chromosome
 Each sperm produced by a testicle contains
either one X chromosome OR one Y
chromosome
 The X chromosome is larger than the Y
chromosome and holds more genes
 Each animal has its own sex chromosomes and
sex determination based on those
chromosomes

Question: What is the probability
that your parents will have a boy
or girl?
 XY (dad) x XX (mom)

X
X
XX
Y
XY
Phenotype:
50% boy
50% girl
X
Genotype:
XX
XY
50% XX
50% XY
Question?
If my parents have 5 boys in a row, what
is the chance they will have a girl the next
time?
50%
Sex-linked gene:
Some traits are carried on the sex
chromosomes. Genes on the X or Y
chromosomes are sex-linked genes.
 This term is historically used to describe traits
housed on the X chromosome
 These traits are passes on from parent to
child. Sex- linked genes can be recessive or
dominant.

MALES are more likely to have a sex-linked
trait because they only have ONE X and Y.
The allele is USUALLY on the X
chromosome.
 Fathers pass on to daughters only; mothers
pass to sons and daughters
 Ex. colorblindness, hemophilia, hairy ears,
muscular dystrophy

Are you colorblind?
What numbers do you see?
Sex linked Punnett Squares:
Question:
What is the probability that a carrier female and
a colorblind male will have a girl who is colorblind
(b = colorblind, B = normal)?
Xb
Y
Phenotype:
XB
XBXb
XBY
25% normal boy
25% colorblind boy
25% normal girl
Xb
25% colorblind girl
XbXb
XbY
Try this one on your own
Question:
What is the probability that a homozygous
(normal vision) female and a colorblind male will
have a girl who is colorblind (b = colorblind, B =
normal)?
Parents: XBXB x
Xb
X bY
Y
Phenotype:
XB
XBXb
XBY
XB
XBXb
XBY
50% normal girls
50% normal boys
X-Inactivation
Since females have 2 X chromosomes, one
is inactivated
 During development, each cell of the
embryo randomly inactivates one
 Every cell may have a different X
inactivated (ex. Tortoiseshell Cat)
 Barr-bodies - inactive X chromosomes lies
along the inside of the nuclear envelope

Carrier – person who has one recessive
allele and one dominant allele for a trait or
heterozygous for that trait (only women
can be carriers).
Example
Hemophiliac carrier XHXh
Colorblind carrier
XBXb

Carriers do not show that particular trait
phenotypically but have a chance to pass
the trait on to their child.
Carrier – half colored
Reading a Pedigree
Task 1: Genotyping a pedigree chart
Task 2:
Go to the lab tables.
Each person should have one answer sheet.
Lets do the first one together.
As a group, finish analyzing the pedigrees. If
you have extra time, work on conclusion
questions (homework if not completed in
class).
?
Ticket Out

Obtain a paper with a problem that asks
you to create your own pedigree… due on
your way out of the classroom.
What is a karyotype?
Picture of your
chromosomes
 Arranged from largest to
smallest
 quickly identify
chromosomal changes
 http://www.biology.arizo
na.edu/human_Bio/activi
ties/karyotyping/karyotyp
ing2.html

Diagnose the karyotypes in the back of
the room at your table.
Make sure to include:
• Case number
• Boy or girl
• Number of chromosomes
• Normal or abnormal
(if abnormal, what is the problem?)
Genetics Disorders and
Mutations
Mutations …
are changes in the
genetic material
 can be good or bad
 can be on a single
gene or the whole
chromosome

Genetic Disorder –
abnormal condition that a person inherits
through genes or chromosomes.
They are caused by mutations or changes
in a person’s DNA.
Write down 3 disorders that have
affected someone you know.
Cystic Fibrosis




Recessive genetic disorder where the body produces abnormally
thick mucus in the lungs and intestines making respiration and
digestion difficult
Caused by a mutation in a gene. Body produces mucus which builds
up in the breathing passages of lungs and pancreas (the organ that
helps to break down and absorb food)
One in four babies are born with cystic fibrosis
Most common among Northern European descent
Sickle Cell Anemia




Sickle cell is a recessive genetic disorder that affects
the blood’s hemoglobin. Hemoglobin is the protein
in your blood that carries oxygen.
Sickle-cell anemia is caused by a point mutation in
protein chain of hemoglobin, replacing the amino
acid glutamic acid with the amino acid valine
The ‘sickle shape’ of the cell causes it to form clots
easily and the protein doesn’t allow the red blood
cell to carry very much oxygen.
Most common among African American descent
Famous People with Sickle Cell Disease
Miles Davis, jazz musician.
Paul Williams, singer (The Temptations)
Georgeanna Tillman, singer (The Marvelettes)
Tionne "T-Boz" Watkins, singer (TLC)
Hemophilia
Hemophilia is a genetic disorder in which a person’s
blood clots VERY slowly or not at all.

A person with hemophilia can bleed to death from a
paper cut or scrape.

This is a recessive sex-linked disorder on the X
chromosome.
– Queen Elizabeth suffered from this disorder.

This man received a
vaccine. This is what having
hemophilia did to is body.
Down Syndrome


Down Syndrome is a genetic disorder that
occurs when an individual receives an extra
copy of a chromosome.
A mistake occurs during Meiosis I: the
chromosomes failed to separate correctly (nondisjunction) therefore leaving an extra copy of
chromosome #21.

Doctor’s use tools like amniocentesis
and karyotypes to help detect most
diseases.
4 Types of Genetic Disorders
1. Single gene
– Change in the DNA sequence
– More than 6000 known disorders
– Autosomal or sex linked
– 1 in 200 births
Examples:
cystic fibrosis, sickle cell anemia, Marfan
syndrome, Huntington’s disease
Types of Genetic Disorders
2. Multi-factoral
– combination of environmental factors and
mutations in multiple genes
– more complicated
Examples:
heart disease, high blood pressure,
Alzheimer’s disease, arthritis, diabetes, cancer,
and obesity
Types of Genetic Disorders
3. Chromosomal
– abnormalities in chromosome structure as
missing or extra copies or gross breaks and
rejoining
Example:
Down Syndrome
Types of Genetic Disorders
4. Mitochondrial
– rare type of genetic disorder
– caused by mutations in the non-chromosomal
DNA of mitochondria
?
Here are some genetics disorders,
some you have heard about and
some you haven’t.
Turners Syndrome
1 in 5,000 births
45 chromosomes
X only
#23 Monosomy
Nondisjunction
Turners Syndrome
96-98% do not survive to birth
No menstruation
No breast development
No hips
Broad shoulders and neck
Cri-Du-Chat Syndrome
1 in 216,000 births
46 chromosomes
XY or XX
#5 Deletion of lower
arm
Cri-Du-Chat Syndrome
Moon-shaped face
Heart disease
Mentally retarded
Malformed larynx
Normal lifespan
Aniridia-Wilms Tumor
Syndrome
1 in 50,000,000 births
46 chromosomes
XY or XX
#11 Deletion of upper arm
Aniridia-Wilms Tumor Syndrome
Mentally retarded
Growth retarded
Blindness
Tumors on kidneys
Short lifespan
Thirteen Q Deletion
Syndrome
1 in 500,000 births
46 chromosomes
XY or XX
#13 Deletion of lower arm
Thirteen Q Deletion Syndrome
Mentally retarded
Deformed face
No thumbs
Heart disease
Short lifespan
Prader-Willi Syndrome
1 in 5,000,000 births
46 chromosomes
XY=97%
XX=3%
#15 Deletion of lower arm
Prader-Willi Syndrome
Small bird-like head
Mentally retarded
Respiratory problems
Obesity
Short lifespan
Eighteen Q Deletion
Syndrome
1 in 10,000,000 births
46 chromosomes
XY or XX
#18 Deletion of lower arm
Eighteen Q Deletion Syndrome
Mentally retarded
Heart disease
Abnormal hands and feet
Large eyes
Large ears
Normal lifespan
Cat-Eye Syndrome
1 in 1,000,000 births
46 chromosomes
XY or XX
#22 Deletion of bottom
arm
Cat-Eye Syndrome
Fused fingers and toes
Mentally retarded
Small jaw
Heart problems
Normal lifespan
Four-Ring Syndrome
1 in 10,000,000 births
46 chromosomes
XY or XX
#4 Inversion
Four-Ring Syndrome
Cleft palate
Club feet
Testes don’t descend
Short lifespan
Down Syndrome
Trisomy
1 in 1,250 births
47 chromosomes
XY or XX
#21 Trisomy
Nondisjunction
Down Syndrome
Short, broad hands
Stubby fingers
Rough skin
Impotency in males
Mentally retarded
Small round face
Protruding tongue
Short lifespan
Patau’s Trisomy
Syndrome
1 in 14,000 births
47 chromosomes
XY or XX
#13 Trisomy
Nondisjunction
Patau’s Trisomy Syndrome
Small head
Small or missing eyes
Heart defects
Extra fingers
Abnormal genitalia
Mentally retarded
Cleft palate
Most die a few weeks after birth
Edward’s Trisomy
Syndrome
1 in 4,400 births
47 chromosomes
XX=80%
XY=20%
#18 Trisomy
Nondisjunction
Edward’s Trisomy Syndrome
Small head
Mentally retarded
Internal organ abnormalities
90% die before 5 months of age
Jacob’s Syndrome
1 in 1,800 births
47 chromosomes
XYY only
#23 Trisomy
Nondisjunction
Jacob’s Syndrome
Normal physically
Normal mentally
Increase in testosterone
More aggressive
Normal lifespan
?
Klinefelter Syndrome
1 in 1,100 births
47 chromosomes
XXY only
#23 Trisomy
Nondisjunction
Klinefelter Syndrome
Scarce beard
Longer fingers and arms
Sterile
Delicate skin
Low mental ability
Normal lifespan
Triple X Syndrome
1 in 2,500 births
47 chromosomes
XXX only
#23 Trisomy
Nondisjunction
Triple X Syndrome
Normally physically
Normal mentally
Fertile
Huntington’s Disease
Caused by a lethal dominant gene in which a
section of DNA on chromosome #4 is repeated
more than usual
 Nerve cells in the brain waste away, or
degenerate
 Two forms – most common is adult onset in
which those affected show no signs until 35 or
40; other is early onset

Huntington’s Disease
Abnormal and unusual movements
 Behavior changes
 Dementia that slowly gets worse, including
 Additional symptoms that may be associated with this
disease:

– Anxiety, stress, and tension
– Difficulty swallowing
– Speech impairment

In children:
– Rigidity
– Slow movements
– Tremor
Color-Blindness
Have trouble seeing red, green, or blue or a
mix of these colors
 Caused by a recessive sex-linked allele
 The cone cells in your eyes do not function
properly or are absent
 You may not see red, blue, or green, or you
may see a different shade of that color or a
different color
 Doesn't change over time.

Color-Blindness
Tay-sachs
Autosomal recessive disorder because of
mutation on chromosome 15
 Infants typically appear normal until 3 to 6
months:
 Other forms of Tay-Sachs disease are very rare.

–
–
–
–
Tay-sachs Disease
development slows and muscles used for movement weaken
lose motor skills such as turning over, sitting, and crawling
develop an exaggerated startle reaction to loud noises
Eventually experience seizures, vision and hearing loss,
intellectual disability, and paralysis
– eye abnormality called a cherry-red spot, which can be
identified with an eye examination, is characteristic of this
disorder.
– Children with this severe infantile form of Tay-Sachs disease
usually live only into early childhood.
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Diagnose the karyotypes cont.
You have already described what is abnormal (if
applicable) about the karyotypes, now you must
identify what genetic disorder (if any) is portrayed using
the knowledge you just received.