Biology Chapter 11
Human Genetics
Human Genetic Disorders
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Can be recessive disorders
In some cases, can be dominant disorders
We are going to look at some examples of some genetic
disorders.
NO TEST this chapter. Your test instead will be:
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Pick a genetic disorder to research
Complete one of the following:
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3-5 page typed double-spaced paper on your research
Slide presentation with slide number between 18-23 slides
Work cited page (or slides) does not count toward total but is
necessary to document your work.
Cystic Fibrosis
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Most common inherited genetic disorder among white
people. 1 in 20 carries the recessive allele.
1 in 2000 babies born with CF.
Symptoms:
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Thick mucus builds up in lungs, can damage pancreas.
Movement of salts and water across cell membranes affected.
Medical advances have helped, but disorder is still fatal.
Huntington’s Disease
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Caused be a dominant gene.
Why does this matter?
Estimated that 25000 Americans have the disorder.
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Changes in coordination occur
Difficulty thinking through problems
Depressed irritable mood
Diminished speech and difficulty swallowing.
In late stages, individual is totally dependent on others.
Sickle-Cell Anemia
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Found most often in blacks.
1 in 500 African-Americans has the disorder
Hemoglobin structure is changed.
Severe pain, fever, and weakness are symptoms of the
blood cells becoming caught in capillaries.
Strokes that result in paralysis can result.
Analysis
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Solving genetic problems is similar to putting together a
puzzle.
Some are simple, if the mutant gene is singular.
Diabetes mellitus, heart disease, and some personality
disorders are the result of multiple mutant genes.
Estimated every person carries 5 to 8 harmful genes.
Most of the harmful alleles are recessive.
Also thought that most zygotes carrying harmful alleles
never complete development.
3/5 of all pregnancies in humans are aborted (most
naturally)
Heterozygote Superiority
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Sometimes, the heterozygous combination of alleles is an
advantage: Sickle cell anemia
In Africa, as many as 40% carry the heterozygous form.
Although this makes hemoglobin function less efficient,
for a simple reason, it also makes the individual resistant
to malaria.
The parasite that causes malaria does not do well in
sickle shaped cells.
Survival rate of heterozygotes is higher than those who
don’t carry the gene for the disorder.
Chromosome Abnormalities
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Nondisjunction – failure of paired chromosomes to
separate during meiosis.
Down syndrome - #21 chromosomes fail to separate.
Known as trisomy 21.
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Varying degrees of mental retardation
Usually shorter than normal
Heart, intestinal, or visual problems
Susceptible to infection and increased risk of blood cancer
(leukemia)
Most likely to occur to infants of mothers over 40.
Karyotyping can help in chromosome abnormality
detection.
Sample Kayotype
11.2 Prevention
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Genetic counseling – giving parents information about
chances of their children having a genetic disorder.
What would you do if there was an increased chance of a
child with a genetic disorder?
Diagnosis in the uterus:
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Amniocentesis – needle used to withdraw fluid from the fetus
and karyotype is done. Can be done in 14th week.
Chorionic villus biopsy – 9th week, cells from chorion are
withdrawn.
Ultrasounds and fetoscopy also offer chances for early
detection.