Biology Chapter 11Human Genetics

Human Genetic Disorders 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: Pick a genetic disorder to research Complete one of the following:

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 Most common inherited genetic disorder

among white people. 1 in 20 carries the recessive allele.

1 in 2000 babies born with CF. Symptoms:

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 Caused be a dominant gene. Why does this matter? Estimated that 25000 Americans have the

disorder. 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 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 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 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 Nondisjunction – failure of paired

chromosomes to separate during meiosis. Down syndrome - #21 chromosomes fail to

separate. Known as trisomy 21. 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 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: 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.