Biology 102, Lectures 21 and 22, Study Guide
March 3, 5 and 8 [part?], 2004
TOPIC: Patterns of inheritance (through sickle cell anemia example)
Outline: For a more detailed outline and details, see PowerPoint slides and your own lecture
notes.
I.
II.
Down Syndrome (clarification)
Patterns of Inheritance: Introduction
A.
Why study genetics?
B.
Useful vocabulary
C.
Historical perspective: Gregor Mendel’s studies
III. Patterns of Inheritance: Concepts
A.
Inheritance of single traits
B.
Inheritance of multiple traits
1.
Different chromosome
2.
Same chromosome (linkage)
IV. Sex chromosomes
A.
Overview
B.
Sex linkage
V.
Incomplete dominance
VI. Codominance
VII. Pleiotropy
A.
Sickle cell anemia example
Study questions
1.
What chromosomal abnormality causes Down syndrome? At what phase of meiosis did
the problem occur?
2.
Except for chromosome Pair 21 and the sex chromosomes, having three instead of two
chromosomes dooms a child to die before or shortly after birth because of massive
abnormalities. What feature of Pair 21 allows Down syndrome individuals to survive into
adulthood?
3.
Vocabulary: Define the following terms. Where appropriate, they should be defined and
related to each other. Sketches may be useful, but definitions should be in words and not
just pictures. Note that the book has a glossary containing most/all of these terms, but you
should be sure you really understand these terms and can use them.
a.
Gene
b.
Locus
c.
Trait
d.
Allele
e.
Homologous chromosomes
f.
Homozygous
g.
Heterozygous
h.
i.
j.
k.
genotype
phenotype
Dominant
Recessive
4.
Describe three aspects of Gregor Mendel’s work that were fortuitous in helping him
discover the principles of inheritance.
5.
What was Gregor Mendel’s occupation?
6.
Be sure you can work through problems involving single crosses. This should be easy.
See lecture and text for examples.
7.
You cross two rabbits, one a homozygous dominant for both fur color (brown is dominant,
white is recessive) and eye color (purple is dominant, blue is recessive), the other a
homozygous recessive for these two traits. Determine the genotypic and phenotypic ratios
for the F1 and F2 generations.
8.
You cross two rabbits; one is a homozygous recessive for both fur color and eye color,
while the other is heterozygous for both traits. What are the genotypic and phenotypic
ratios for their offspring (F1 only)? (NOTE: This will give you a different result than
when you cross the two homozygotes or the two heterozygotes. Be sure you can work
through this!)
9.
Be sure you understand and can do all problems given in the related lab.
10.
Make up your own genetics problems. You should be able to do Punnett squares in your
sleep for crosses with both single traits and two traits on different chromosomes.
11.
How are the letters you put at the top and sides of the Punnett Square related to gametes?
12.
What is meant by independent assortment? For two traits to sort independently, what must
be true?
13.
What are “linked” genes?
14.
What process would cause two linked alleles to end up in different gametes during meiosis,
rather than “traveling together”? Is this more or less likely to occur if the genes are close
together on the chromosome?
15.
How do the X and Y chromosomes differ? Which carries more genes? Do they have any
genes in common?
16.
Why are most sex-linked traits carried by the mother but expressed in their sons?
17.
Be able to work through problems involving single sex-linked traits, such as the fruit fly
eye color examples provided in the lecture/text and in lab.
18.
What is incomplete dominance? Provide an example.
19.
What is codominance? Provide an example.
20.
Be sure you understand the human blood type chart, so that you can answer the following
questions without the chart:
a.
b.
c.
d.
What are the possible genotypes that will give someone blood type A? Blood type
B? Blood type AB? Blood type O?
Which antigens (i.e. attached sugars) are expressed in each of these blood types?
To which type of antigen does each produce antibodies? For example, you should
understand that blood type O produces antibodies to both A and B.
You should know which type of blood each of the blood types can accept, and who
each can donate to. Understand especially who the universal donor and universal
acceptors are, and why.
21.
Provide an example where an environmental condition affects the expression of a gene.
22.
Define “pleiotropy”?
23.
The sickle cell example
a.
At the level of the DNA, how does the sickle cell allele differ from the “normal”
allele?
b.
What consequence does this have for the primary structure of the protein
(hemoglobin)? In other words, how does the amino acid sequence differ for the
“normal” vs. the “sickle cell” condition? HINT: Not a big difference…
c.
What consequence does this have for the tertiary and quaternary structure of the
protein?
d.
What is abnormal about the hemoglobin itself for someone with sickle cell anemia?
You should be able to list two abnormalities.
e.
What causes the red blood cells to be sickle-shaped?
f.
What are some of the whole organism effects of sickle cell anemia?
24.
Describe the phenotype of a heterozygote for the sickle allele compared to either
homozygote.
25.
Is this (the sickle cell example) a case of true dominance, incomplete dominance, or
codominance?