Download 14.2_Human_Genetic_Disorders

1 Infer How do genetic disorders such as CF support
the theory of evolution
2 Review Explain two sex chromosome disorders
3 Description Write a paragraph explaining the
process of nondisjunction
CH 14 HUMAN HEREDITY
14.2 Human Genetic Disorders

Changes in DNA sequence can change proteins by
altering the amino acid sequences, which may
affect the phenotype.
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African and European ancestry are more likely to
have wet earwax (dominant form)
Asian or Native American ancestry most often have
the dry form (recessive)
Single DNA base change from guanine (G) to
adenine (A) in the gene for a membrane-transport
protein causes this change.
Disorders Caused by
Individual Genes

Lots of genetic disorders are caused by changes in
individual genes.
Sickle Cell Disease

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Caused by a defective allele for beta-globin
(protein in hemoglobin)
Makes hemoglobin less soluble
Causes hemoglobin molecules to stick together
with low blood oxygen level
Molecules clump into long fibers.
Sickle Cell Disease

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Sickle-shaped cells are more rigid than normal red
blood cells
Get stuck in the capillaries
Blood stops moving through the capillaries,
damaging cells, tissues, and organs.
Cystic Fibrosis

Results from deleting three bases in the gene for a
protein CFTR (cystic fibrosis transmembrane
conductance regulator).
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CFTR normally allows chloride ions (Cl−) to pass
across cell membranes
Deletion causes protein to fold improperly
Misfolded protein is then destroyed.
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Cell membranes unable to transport Cl−
Tissues malfunction
Children have serious digestive problems and
produce thick, heavy lung mucus.
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One normal copy of the CF allele are unaffected by
CF
Two copies of the defective allele are needed to
produce the disorder.
Huntington’s Disease
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Caused by a dominant allele for a protein found in
brain cells
Allele for this disease contains a long string of
CAGs (glutamine) repeats over 40 times more
repeats the more severe
Mental deterioration and uncontrollable
movements usually do not appear until middle
age.
Genetic Advantages

In the United States CF allele is found
1
person in 12 of African ancestry
 1 person in 25 of European ancestry
Why that common if it can be fatal if you have 2
copies.

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Most African Americans today are descended from
west central Africa, where malaria is common
Malaria is a mosquito-borne infection caused by a
parasite that lives inside red blood cells.
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1 sickle cell gene- still
heathly
AND are highly resistant
to the malaria parasite.
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Similar relationship between CF and Typhoid.
Chromosomal Disorders
Nondisjunction

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Homologous chromosomes fail
to separate
Results in gametes with an
abnormal number of
chromosomes.

Most common form of trisomy (3 copies of a
chromosome) is Down syndrome (trisomy 21).
Nondisjunction of the
X Chromosomes

Turner Syndrome
 45,
X Karyotype
 Usually short, underdeveloped, and sterile

Klinefelter Syndrome
 47,
XXY karyotype.
Geography of Malaria
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Malaria is apotentially fatal disease transmitted by
mosquitoes. Its cause is a parasite that lives inside
red blood cells. The upper map shows the parts of
the world where malaria is common. The lower
map shows regions where people have the sickle
cell allele.
The map is on the following slide
1.
2.
3.
Analyze Data What is the
relationship between where
malaria and the sickle cell
allele are found
Infer In 1805, a European
expedition tried to find the
source of the Niger River in
Africa. During the expedition
most of them died of malaria.
Why do you think their native
African guides survived
Form a Hypothesis Propose an
explanation why the sickle cell
allele is not found in
populations of southern
Africa.