BIOL. 303 EXAM I 2/13/01
------------------------------------------------------------------------------------------------------------------
Answers are underlined and in boldface. For some questions, a brief
explanation of the correct answer is provided in parentheses. If you have any
questions, please come and see me.
------------------------------------------------------------------------------------------------------------------
1.
If the diploid number of chromosomes for an organism is 24, then the haploid number is
1. 24
2. 12 …..(2n= 24, therefore n=12)
3. 48
4. 36
2.
A normal human cell has a diploid number of 46. A normal human germ line cell undergoing
meiosis contains how many bivalents during prophase I?
1. 46
2. 92
3. 23…(the number of bivalents =n, which in this case is 23 since 2n=46)
4. cannot be determined.
3.
A place in the eukaryotic cell cycle at which a "decision" is made whether to proceed through the
cell cycle or to arrest cell cycle progression is generally known as
1. S phase
2. G1 phase
3. a checkpoint
4. mitosis
4.
Which step of mitosis leads to significant genetic variation?
1. None. Mitosis produces identical cells.
2. Telophase
3. Prophase
4. Metaphase
5.
When we view a cell under a microscope during mitosis, why do its chromosomes
look like X's?
1. Because when a chromosome coils, it takes on an X-shape.
2. Because each linear chromosome has replicated during interphase.
3. Because homologous chromosomes join as tetrads during mitosis.
4. Chromosomes are always X-shaped because the maternal and paternal
contributions are linked together at the centromere.
6.
Which of the following statements about meiosis is false?
1. the products of meiosis are usually haploid.
2. somatic cells enter into meiosis….(only germ line cells undergo meiosis)
3. during meiosis, crossing over may occur between homologous chromosomes.
4. all of the above.
7.
Which of the following statements about homologous chromosomes is true?
1. They are identical.
2. In each cell there are two pairs of homologous chromosomes--one pair from each parent.
3. The homologous pairs of chromosomes pair up and undergo recombination during prophase of
mitosis.
4. They contain all of the same genes but not necessarily the same alleles.
8.
A human gamete
1. normally contains one sex chromosome.
2. cannot be aneuploid.
3. is produced following the second division of mitosis.
4. usually contains two chromosomes from each pair of homologous chromosomes.
9.
With respect to the indicated genes, how many different kinds of gametes can be produced by an
individual with the genotype AABBCCDdEe? (Assume independent assortment.)
1. 32
2. 4
(only genes D and E are heterozygous)
3. 5
4. 2
10.
To say that a group of plants "breeds true for tallness" means that
1. tall plants, when selfed (self-fertilized), give rise to tall plants…(true breeding =
homozygous)
2. dwarf plants give rise to dwarf and tall plants.
3. tallness must be dominant to dwarfness.
4. tallness is a wild-type trait.
11.
In each of Mendel's monohybrid crosses of pea plants, the trait that was observed in the F 1
generation
1. illustrated the principle of independent assortment.
2. was "tallness."
3. appeared in 9/16 of the plants in F2 generation.
4. was a dominant trait.
12.
An allele
1. is a form of a gene.
2. can encode only a dominant trait.
3. cannot display codominance with another allele.
4. all of the above.
13.
A 9:3:3:1 ratio of phenotypes in the F2 generation of a dihybrid cross
1. holds true only for genes on the same chromosome.
2. indicates that the dihybrid cross is basically equivalent to two independent monohybrid crosses.
3. is not indicative of independent assortment.
4. indicates that an epistatic relationship exists between the two genes under investigation.
14.
Two normal looking Drosophila were mated and produced 41 gold (normal) and 13 ebony-bodied
flies. Which of the following statements is most likely true?
1. one of the parental flies was homozygous for gold
body color.
2. ebony and gold assort independently.
3. epistasis exists between gold and ebony body color.
4. ebony body is a recessive trait. …(3:1 ratio is classic monohybrid cross ratio)
15.
A plant heterozygous for three unlinked genes (genotype AaBbCc) is self-crossed. What
percentage of the offspring should have the phenotype ABC?
1. 1/8
2. 1/27
3. 1/64
4. 27/64…(it's just 3/4 X3/4X3/4)
16.
A tall, violet plant is crossed with a dwarf, white plant and all of the F1 offspring are tall, violet.
The F1 plants are selfed to produce the F2 generation. What fraction of the F2 generation would you expect
to be tall, white? (Assume independent assortment.)
1. 1/4
2. 9/16
3. 3/16….(9:3:3:1 ratio!)
4. can't tell because partial dominance may be at work.
17.
Suppose you had an organism displaying the phenotype BC. In order to determine the genotype of
this individual, with which of the following genotypes should you cross it in a test cross?
1. bbcc
2. BBCC
3. BBCc
4. BbCC
18.
Color blindness is a sex-linked recessive trait. If a woman is color blind:
1. her mother must have been color blind.
2. her paternal grandmother was either color blind or was a carrier for color blindness….( the
woman got a bad X chromosome from her Dad, who got it from his Mom)
3. her paternal grandfather must have been color blind.
4. her father may not be color blind.
19.
A woman and a man are both heterozygous for freckles (the dominant condition). If
they have one child, what are the chances that it will also have freckles?
1. 25%
2. 50%
3. It will depend on the sex of the child.
4. 75%
20.
A man with blood type AB is married to a woman with blood type A who has three children with
blood types A, AB, and B. Which child could the man reasonably suspect was not his own on the basis of
blood groups?
1. the child with A blood.
2. the child with AB blood.
3. the child with B blood.
4. all of the children could be his.
21.
True-breeding red flowers are crossed with true-breeding white flowers to produce all pink
flowers in the F1 generation. This is likely a result of
1. partial dominance….( partial dominance involves "blending" of phenotypes)
2. codominance.
3. incomplete penetrance.
4. recombination.
22.
Suppose you are performing a trihybrid cross and want to determine if the phenotypes observed in
the F2 generation fall into a 27:9:9:9:3:3:3:1 ratio indicative of independent assortment of the three genes
under study. Which statement is correct?
1. there should be 8 distinct genotypes in the F2 generation.
2. you would have to be crazy because there is no such thing as a trihybrid cross.
3. if a X2 test were used in your analysis of the phenotypic classes, then 7 degrees of freedom should be
used….(df= n - 1)
4. if independent assortment is occurring, then the three genes must be sex-linked.
23.
You perform a X2 test on the phenotypic classes in the F2 generation of the cross described in
question 22 to test the hypothesis that the genes assort independently. After determining a value for X 2, you
use a X2 table and find that the value of p is equal to 0.01. This means
1. at least one of the three traits is probably lethal.
2. the hypothesis that the traits assort independently can be rejected….(p has to be greater
than 0.05 in order to NOT reject the hypothesis)
3. the three traits likely assort independently.
4. Mendel was wrong.
24.
In a human pedigree, a male is symbolized by a
1. circle
2. square
3. diamond
4. triangle
25. In a pedigree, if an individual is affected with a disease but neither of his or her parents are affected,
we know that the trait is:
1. Recessive.
2. Autosomal dominant.
3. Sex-linked recessive.
4. Affected by two or more genes.
26.
Which of the following is an example of independent assortment?
1. More men than women are colorblind
2. Some traits are more likely to be inherited than others.
3. If you have red-hair, you are no more or less likely to be tall than anyone else
4. A diploid individual only passes on one copy of a gene to her offspring.
27.
In humans, sex is determined by
1. the number of X chromosomes.
2. the presence or absence of a Y chromosome.
3. the presence or absence of an X chromosome.
4. the ratio of X chromosomes to autosome sets.
28.
Consider a person who has a genotype designated 48,XXXY. This person
1. is phenotypically female and has two extra X chromosomes.
2. is tetraploid and has two extra X chromosomes.
3. has three Barr bodies per cell nucleus.
4. is phenotypically male and has two extra chromosomes.
29. A Barr body
1. is an inactivated Y chromosome.
2. contains no DNA.
3. ensures that males and females have equal "doses" of the genes on the X chromosome.
4. is visible only in males.
30. Dosage compensation
1. must occur when one sex has more copies of a gene or genes than the other sex.
2. is a problem in species that have more autosomes than sex chromosomes.
3. cannot be directed by enhancing X-chromosome activity.
4. works in the same way in all animals.
31.
If a person has trisomy for chromosome 13, a somatic cell from this individual has a total of how
many chromosomes?
1. 23
2. 24
3. 69
4. 47…(one extra chromosome)
32. Chromosomal inversions can bring about phenotypic changes. This is best explained by the
phenomenon known as:
1. polyploidy.
2. genetic deletion.
3. position effect.
4. aneuploidy.
33.
Albinism, lack of pigmentation in humans, results from an autosomal recessive gene. Two parents
with normal pigmentation have an albino child. What is the probability that their next child will be a
normally pigmented boy? (Please think carefully before you answer).
1.
3/8….(3/4 chance that the child is normally pigmented, 1/2 chance that the child is a boy)
2. 1/4
3. 1/8
4. none of the above
34.
A dairy farmer and a geneticist were looking out the farmer's living room window and saw a
mahogany-colored Ayshire cow with its newly born mahogany calf. The farmer remarked that he was
interested to learn the sex of the calf. The geneticist (a former student of BIOL. 303) explained that in
Ayshires the genotype AA is mahogany and aa is red, but the genotype Aa is mahogany in males and red in
females. Based on this information, what is the sex of the calf?
1. female
2. male
3. there's not enough information to tell
4. calves have no gender.
35.
If a trait appears to be transmitted exclusively from fathers to sons, then the gene responsible for
this trait is best described as:
1. Y-linked.
2. X-linked.
3. sex-linked.
4. autosomal.
36.
A sex-linked lethal recessive gene, let (lethal), in Drosophila causes death during embryogenesis
when homo- or hemizygous. If a female heterozygous for let is crossed with a wildtype male, what will the
sex ratio of the adult progeny be?
1. 2 females: 1 male…(half the males die)
2. 1 female: 1 male
3. 1 female: 2 males
4. 3 females: 2 males
37.
The Bombay phenotype illustrates
1. that IA and IB are dominant over IO and codominant with respect to each other.
2. that genotype and phenotype are always linked.
3. that under some circumstances, other factors may override the genotype in
question, producing phenotypes that do not match the genotype.
4. the difference between the A and B blood types.
38.
If epistasis exists between two genes, then the genes
1. together control two traits.
2. are likely on the same chromosome.
3 together influence the expression of a single trait.
4. likely yield a 9:3:3:1 phenotypic ratio in the F2 generation of a dihybrid cross.
39. In a human pedigree, if a trait is predominantly displayed by males and only infrequently
displayed by females then the trait is most likely
1. autosomal dominant.
2. Y-linked.
3. X-linked recessive.
4. good.
40.
Familial Down syndrome is caused by:
1. a centric fusion.
2. position effect.
3. nondisjunction.
4. genomic imprinting.
THAT'S ALL!