ANTHR1 FA 09 – First Exam - Answers to Essay Questions
I selected answers from those submitted by students as the “benchmark” for what constitutes an A.
NOTE: When grading I used the WRONG KEY for Question J. If you answered J and I wrote that you answered a question I did
not ask, please bring your exam to me so that I may assess you answer.
A. What are the major ideas in the theory of natural selection?
1. NOT all born equal, have lots of different genes so... some of us are tall, short, light skinned, dark skinned, blood type
A or B or O or AB.
2. There is only so much stuff in the world: space, shelter, water, food, love etc. The planet is a finite place.
3. Sexually reproducing organisms are capable of having more offspring than can survive. Therefore not all individuals
in the population can contribute an equal number of offspring to the next generation. Some die; the ones who live are
the ones who have the “right” traits (in a particular environment).
4. Limited stuff means some of us get and some of us do not. Because there are so many and they so are different and
that there is a limited amount of stuff, space, etc., there is COMPETITION for all of this stuff, space, etc.
5. Those who get space, food, stuff, etc. (because their phenotypes are better suited than others for life in any particular
environment), have children and pass on their traits (especially those that contributed to their survival); those that
don't, die.
6. Because of 1 – 5, populations tend to evolve toward phenotypes that are better adapted to their environment.
B. Using an example, explain how natural selection works.
There are so many examples, but many of you selected the elephant story. So here’s what you need to say. There’s a
population of 100 elephants; most (perhaps 90) have tusks, a few (perhaps 10) do not have tusks. Males use tusks in
competition for access to females. Males with tusks can out compete males with no tusks, thus contributing more often
to the next generation. At some point a predator enters the environment and begins killing the tusked elephants, thus
creating more opportunity for non-tusked males to mate with females. Over time more and more tusked males are
killed, more and more non-tusked elephants get a chance to mate. After sometime, there are now fewer tusked
elephants (perhaps only 70) and more non-tusked (perhaps 30) than in the original population.
C. Evolution is a change in the relative frequencies of alleles in a population from one generation to the next.
You were to answer this question by referring back to B. Having tusks is either a homozygous dominant (TT) or
heterozygous condition (Tt); no tusks is homozygous recessive (tt). In a population of 100 elephants with 90 tusked and
10 non-tusked, there are at least 90 T alleles and 20 t alleles. As the tusked elephants are killed, and the non-tusked
elephants reproduce more often, the T alleles decrease in frequency and the t alleles increase.
D. Define an allele in terms of its function.
An allele is a segment of a DNA molecule that codes for the production of a protein.
E. What are nucleotides? Sugar+phosphate+base (basic building block of DNA / RNA molecule. What are codons? A
linear sequence of three nucleotides (can also say three bases) that specifies (names, stands for, codes for) a particular
amino acid. What’s the relationship between them? Just said that
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F. What’s a hominid? Be very specific. An habitual upright bipedal primate (humans)
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G. Evolution is a change in the relative frequencies of alleles in a population from one generation to the next. Natural selection
is one way this happens. Name and explain three other ways. Mutation (change in a gene); gene flow or migration (mixing
of genes of two distinctive populations; genetic drift (random change in gene pool)
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H. Explain the differences (Note the use of the plural) between mitosis and meiosis. Mitosis is body cell division and ensures
that all descendant cells have the exact same number of chromosomes. Meiosis is sex cell division and ensures that each
sex cell has 1/2 the chromosome number. Ensures variation in the next generation
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I. Explain segregation and independent assortment. Segregation (during meiosis, paired alleles separate from each other
and one allele goes in one sex cell and the other allele goes in a different sex cell); Independent assortment (the
distribution of alleles on one set of chromosomes is totally independent of the distribution of alleles on other
chromosomes.
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J. What are the three primary roles of DNA? Carrier of the genetic recipes (code); cell replication and division; protein
synthesis? NOTE: If I marked your exam as having answered the WRONG QUESTION, please come and see me
ASAP. I used the WRONG key for your exam. My apologies.
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K. What animal species is humanity’s closest genetic relative? How close? Chimpanzees. 98-99%
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L. How does being heterozygous for hemoglobin protect one against malaria? Because one of your alleles (S) causes red
blood cells to sickle if you’re bitten by a malaria carrying mosquito. Sickled cell is removed from the body, along with
the malaria bug.(
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M. Coding side of an allele: ATTCGCACGTTA, what’s coding sequence for mRNA? UAAGCGUGCAAU
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N. Distinguish between homozygous and heterozygous. Homozygous means both of your alleles (for a particular trait) are
the same; heterozygous means both of your alleles (for a particular trait) are different.
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O. A woman who is blood type B gives birth to a child who is blood type O. She has accused a type A man of being the father.
Is he? Show or explain your reasoning. He could be because the genotype for blood type A can be either AA or AO. And
the genotype for blood type B can be either BO or BB. If the woman is heterozygous and the man is heterozygous then
the child could be OO.
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