Transcript Sex linked traits and autosomal diseases

Sex-Linked Genes
Review: Sex chromosomes determine sex
II. Sex-linked traits
A. First discovered by T. Morgan
in fruit flies (Drosophila melanogaster)
B. He figured out that the gene for white
eyes was carried on the X chromosome
C. The human X chromosome carries many
genes whose mutated forms cause several
diseases:
Recently discovered, prostate cancer
D. Human’s carry genes for color vision on the X
chromosome.
A Y chromosome
is unable to cover
up the defect
What do you see?
You should see a 26. Some will see a
2 & others a 6.
Some people see nothing
Can you trace a line from one "X" to the other?
Someone with normal color vision will trace a orange/brown purple
line and those with a slight deficiency will follow a different path.
X
X
What do you see?
Only colorblind people can see a 45
III. Sex-linked Punnett squares
A. Hemophilia is carried on the X
chromosome and is sex linked.
B. Make a key:
XHXH = normal female
XHXh = female carrier
XhXh = female with hemophilia
XHY = normal male
XhY = male with hemophilia
Cross a normal male with a heterozygous
female carrier.
XHY
XHXh
H
X
h
X
XH
XH XH
Y
XHY
H
h
X X
h
X Y
XHXh
XHXh
XH
Xh
Y
Xh
XHXh
XH
Xh
Xh
XHXh
XhXh
Y
XHY
XhY
Gene Linkage
• Thomas Hunt Morgan
- worked with fruit flies
– some traits appeared to be inherited together (gene linkage)
– found that fruit flies have 4 pairs of chromosomes.
• Each of the 4 groups of linked traits matched one of the
chromosome pairs.
– Concluded that chromosomes, not genes sort
independently during meiosis.
– Also concluded that due to crossing over, some
chromosomes may exchange homologous genes during
meiosis causing more diversity.
Autosomal Recessive Diseases
A. Caused by the inheritance of 2 recessive
genes.
1. PKU (Phenylketonuria) – defect
found on chromosome 12. Too much
phenylalanine in body, lack of skin
pigment, mental retardation (first one
discovered)
2. Albinism – . 3 types - found on
chromosomes 3, 9, or 15.
no pigment in skin, hair
and eyes
3. Cystic Fibrosis – Defect found on
chromosome 7. Excess mucus in lungs.
4. Tay-Sachs – Defect found on
chromosome 15, common in central and
eastern european jews. Liquid
accumulation in brain cells, mental
problems, blindness, early death.
Autosomal Dominant Diseases
A. If a gene for the disease is inherited, the
person inherits the disease
1. Achondroplasia – Dwarfism. Defect
found on chromosome 4.
2. Hypercholesterolemia – too
much cholesterol in blood. Defect
on chromosome 13
3. Huntington’s Disease – Mental
deterioration, uncontrollable
movements, symptoms appear in
middle age. Defect found on
chromosome 4.
V. CoDominant Diseases
A. People who are heterozygous
for blood cells inherit the disease
1. Sickle Cell Disease – an individual
inherits a dominant gene for normal blood
and a recessive defective gene (may also
inherit 2 recessives to get disease). A
defect in 1 base in the DNA is missing on
chromosome 11 causes the body to
makes glutamic acid instead of valine.
Some red cells are made sickle shaped.
Characteristics of Sickle Cell Disease
• A common genetic disorder found in
African Americans.
– Red blood cells have a bent twisted
shape
– Their rigid shape causes them to get
stuck in capillaries, and blood stops
flowing damaging tissues and organs
– Hemoglobin: a protein that carries
oxygen in red blood cells
• In sickle cell disease hemoglobin is
abnormal and the molecules stick
together
– When the body kills sickle cells it also
kills the parasite that causes Malaria
(benefit?)
XII. Other Genetic Disorders
• Cystic Fibrosis: most common among people
with ancestors from northern Europe
• Caused by a recessive allele on chromosome 7
• Serious digestive problems and thick heavy
mucus that clogs lungs and breathing
passageways
• http://topdocumentaryfilms.com/treeman-searchfor-the-cure/
• http://www.youtube.com/watch?v=renb0qQR7cA
• http://health.discovery.com/videos/medicalmysteries-vod-treeman-disease.html