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BIO 184
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Fall 2006
STUDY GUIDE FOR EXAM 3
Use the study questions below to help guide you when studying for the final
exam. I encourage you to come see me during office hours to ask questions and
clarify concepts. I will also be happy to answer questions by e-mail as long as
the required answers are reasonably short and do not require diagrams.
I.
MENDELIAN INHERITANCE (Lecture 9)
1.
What was the blending theory of inheritance and how did Mendel’s experiments
disprove this theory? What did Mendel’s experiments demonstrate instead?
2.
Be able to carefully and accurately state Mendel’s two laws: Law of Segregation and
Law of Independent Assortment. Know how his monohybrid and dihybrid
experiments in the garden pea allowed him to arrive at these laws.
3.
Be able to list at least 3 advantages of the garden pea as a model organism in
genetics.
4.
Be able to use and define the following terms: monohybrid, dihybrid, homozygous,
heterozygous, genotype, phenotype, linked assortment, independent assortment,
5.
Be able to use Punnett Squares and the Product Rule to predict the outcome of
genetic crosses. You should be able to do this for typical Mendelian crosses but also
for any other type of cross involving one, two, or three traits.
6.
Be able to predict the number of gametes that will be produced by an individual.
7.
Know how to follow sex-linked traits through a cross. Be able to use the proper
nomenclature and predict the offspring of such crosses.
II.
MOLECULAR BASIS FOR DOMINANCE AND RECESSIVITY (Lecture 10)
1.
What are the most common molecular explanations for recessive mutations? Why
are most mutations recessive? How does this help explain why organisms with large
genomes opt for diploidy?
2.
What is PKU? Which enzyme is defective in this disease? If left untreated, what
happens to children who lack the enzyme?
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3.
Why should women with PKU remain on a phenylalanine-free diet throughout their
child-bearing years?
4.
Why are children with PKU often more fair-skinned and fair-haired than their nonaffected siblings?
5.
Be able to give an example of a recessive human genetic disease caused by the loss
of structural protein that is present in excess in normal individuals.
6.
What is a poisonous allele? Be able to explain why such an allele is dominant and be
able to provide one good example of a disease caused by this type of allele.
7.
What is a rate-limiting enzyme? Be able to explain why mutations in genes coding
for such enzymes are often dominant.
8.
What is acute intermittent porphyria? What enzyme is involved?
9.
What is haploid insufficiency of a structural protein? Be able to give an example.
10.
Be able to give examples of recessive alleles that also show dominance.
11.
Be able to give examples of dominant alleles that are really incompletely dominant.
12.
By what two mechanisms can homozygotes for dominant disease alleles be
produced?
13.
Be able to explain why the sickle cell anemia allele is dominant and recessive (at the
macromolecular level and under all levels of oxygen pressure) at the same time.
III. EXTENSIONS OF MENDEILIAN INHERITANCE (Lecture 11)
1.
Be able to use and define the following terms: dominant allele, recessive allele,
wild-type allele, mutant allele, lethal allele, conditional lethal allele, semi-lethal
allele.
2.
Be able to explain why most mutations are recessive.
3.
Understand how lethal alleles (including all the sub-categories of lethal alleles) can
affect the outcome of genetic cross data.
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4.
What is incomplete dominance? Be able to predict the outcomes of crosses where
the alleles at a locus have this type of relationship. Be able to use the correct
nomenclature and understand, at the molecular level, why the alleles might interact
in this manner.
5.
What are multiple alleles? Be able to give some examples.
6.
Be able to define overdominance and give at least one example. What three models
help to explain overdominance at the molecular level?
7.
Be able to use and define the following terms: incomplete penetrance and variable
expressivity. Understand the difference between them and be able to articulate it.
8.
Be able to define the following terms: sex-influenced and sex-limited traits. Be
able to follow a sex-influenced trait through a pedigree and predict the phenotypes
of offspring.
9.
Understand how Mendelian F2 phenotypic ratios from a dihybrid cross can change
when two genes control the same trait. Understand how the following ratios can be
generated: 15:1, 9:7, 13:3 and be able to work with genetic crosses that involve
these forms of gene interaction.
IV.
LINKAGE AND GENETIC MAPPING IN EUKARYOTES (Lecture 12)
1.
Be able to define and use the following terms: parental (non-recombinant),
and non-parental (recombinant).
2.
What is gene linkage? Why is a test cross used to map the distance between
genes along chromosomes?
3.
Be able to examine the data from a dihybrid test cross and map the distance
between the two genes.
4.
What is a centiMorgan (cM) and what does it represent?
5.
Be able to examine the data from a trihybrid test cross and map the
distance between the three genes, indicating which gene is in the middle.
V.
EPIGENETIC INHERITANCE (LECTURE 8)
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1.
Be able to define epigenetic, X-inactivation, and genomic imprinting.
2.
What gives rise to the unusual mottled coat pattern of tortoise shell cats? (Know
the details and be able to draw a diagram.) Why are such cats almost always
female?
3.
What is dosage compensation and why is it necessary in mammals? How do placental
and marsupial mammals differ in the way they achieve dosage compensation? How
does Drosophila achieve it?
4.
What is a Barr body? What is the Lyon Hypothesis?
5.
Be able to describe the experiment of Davidson, Nitowsky, and Childs that provided
strong support for the Lyon Hypothesis.
6.
How is the X chromosome inactivated at the molecular level in mammals? What is
the role of the Xic in this process? Be able to draw out the Xic and describe what
the Xist and TsiX transcripts do.
7.
What are pseudoautosomal genes and where are they located?
8.
Be able to describe the evolutionary logic behind genomic imprinting. What types of
genes tend to be imprinted and why?
9.
How does imprinting work through the generations?
10.
What is the role of DNA methylation in imprinting?
11.
Why did “CC”, the first cloned cat, look different from her tortoise shell mother?