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Academic Integrity in Biology 100/101

I have read and understand Part #4 of the University of Illinois Student Code, which deals with Academic Integrity.

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Answers will be linked to the Take-Home Assignment web page shortly after this assignment is due.

Don't overlook the links to web resources and references to text pages below that might be useful in answering these questions. Activities in lecture, discussion, and laboratory classes will also address these questions.

Completion of these questions will help you achieve most of the objectives for lectures #11, #12, and #13

Question #1. Autosomal Recessive Trait (5 points)

Tay-Sachs disease is an autosomal recessive disorder that results in a degeneration of the nervous system, producing symptoms at about 6 months of age. Affected children loose hearing, sight, and the ability to move. Children with Tay-Sachs disease normally die by age 3.

The gene involved in this disease is HEXA, located on chromosome #15 (8th from the bottom of the right-hand list of gene locations). The normal, dominant allele for the HEXA gene codes for the alpha subunit of the enzyme β-hexosaminidase. The HEXA enzyme is packaged in the lysosomes of nerve cells and breaks down a fatty material called GM2 ganglioside. This fatty material builds up and degrades the nerve cells of a person who has two recessive alleles for the HEXA gene locus.

A couple are interested in having a child, but have learned that the man is a carrier for the disease and the woman is homozygous dominant. What is the chance that their first child will be born a carrier of Tay-Sachs disease?

Show how you arrived at your answer.

Watch segment 3 of the PBS "Nova" program, "Cracking The Code of Life" - "One Wrong Letter". This is an interesting case study of a couple dealing with Tay-Sachs disease

Question #2. Autosomal Dominant Trait (5 points)

Huntington disease is caused by an autosomal dominant mutant allele that produces an abnormally long version of a protein normally present in the brain. The result is a degeneration of nerve function causing loss of motor control and personality changes, ultimately leading to death. The symptoms do not become apparent until a person is in his or her 40s. See also Huntington's Disease Society of America

The gene associated with Huntington disease is located on chromosome #4. The protein that is produced by the gene is "huntingtin". The mutation adds repeated triplets of nucleotides to the gene and produces a longer than normal protein with enhanced, abnormal function. The mutant protein produced by the mutated dominant allele overshadows the function of the normal protein produced by the recessive allele.

A teenage mother learns that her father is developing symptoms of Huntington disease. Her father is heterozygous. Her mother is normal (homozygous recessive).  Is there a chance that the young woman's child has inherited the dominanat Huntington disease gene? (The father of the child is homozygous recessive for the Huntington gene.)

Show how you arrived at your answer.

Question #3. Aneuploidy and Nondisjunction (5 points)

XYY Syndrome (47 XYY) results when a person inherits two sex chromosomes from one of his parents, and a third from the other parent, resulting in a condition in which the individual has three sex chromosomes (an X and 2 Y chromosomes). The affected individual develops as a male. Individuals with this condition generally are of taller stature and may have acne. Some boys with XYY syndrome are physically more active and may have delayed mental maturation.

More information about XYY Syndrome:

See the "Abnormal chromosome numbers" section of lecture outline #12 for more information on aneuploidy and nondisjunction.

Draw a set of diagrams showing how a mistake during meiosis in the development of gametes would result in a gamete with two Y chromosomes.

Show how this would result in a child with the XYY chromosome combination.

Would the mother or the father be "responsible" for this aneuploid condition in a child? Explain your choice.

Question #4. Two Gene Genetics and X-linkage (5 points)

Autosomal Recesive

Fish odor syndrome is a human autosomal recessive condition that results in body odor that resembles rotting fish.

The gene responsible for this genetic disorder is located on chromosome #1 (Zoom in on lower portion of the yellow section below the centromere - nine gene loci below the yellow section on the right-hand list of gene loci.

The fishy odor of people with the "disease" is caused by body emissions of the chemical, trimethylamine (TMA). TMA is a digestion byproduct of foods high in choline, found in fish, eggs, and liver. The dominant allele of the "fish odor" gene produces a protein, which acts as an enzyme that breaks down TMA. The name of the enzyme is flavin-containing mono-oxygenase 3 (FMO3). The recessive allele results from a mutation of this gene that produces a non-functional FMO3 enzyme.

Sex-linked Recesive (X chromosome)

Severe combined immunodeficiency (SCID) is an X-linked recessive disorder. Affected individuals have little or no immune response. You may have heard about the condition as "bubble boy disease". With no immune system, a person is susceptible to recurrent infections from many common diseases that most of us consider minor. A mutated, recessive gene fails to produce an interleukin receptor protein that is necessary for the immune system to function and protect a person from common pathogens.

Bubble Boy disease from MSNBC

A man and a woman are having a child.

The man is a carrier (heterozygous) for the fish odor syndrome and does NOT have SCID.

The woman is also a carrier for the fish odor syndrome. The woman's father has SCID disease. The woman's mother is homozygous dominant for the SCID gene locus.

What is the probability that their child will be a girl who has the fish odor syndrome AND SCID? Show how you arrived at your answer.