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BIOLOGY 350
GENETICS
EXAM ONE
NAME____________
1. During meiosis, the X and Y chromosomes pair as homologs, although there is
never any crossing over between them.
If a gamete is produced that contains two Y chromosomes (by mistake), at which
division did the nondisjunctional event take place?
a. second division
b. first division
c. could have been either
d. the event must have been premeiotic
e. none of these
2. Two homologous chromosomes fail to pair during prophase of meiosis. Which of
the following is likely to occur as a result?
a.
b.
c.
d.
e.
Crossing over is eliminated
Creates a high probability of nondisjunction
both a. and b. are correct
the chromosomes fail to replicate
The cell fails to divide
3. If the F2 of a dihybrid cross gives a 12:3:1 ratio, what will be the ratio of
phenotypes if one takes an F1 individual (from the same cross) and test crosses it?
a. 1:1:1:1
b. 3:1
c. 2:1:1
d. 3:3:1
e. 3:1:1
4. If a couple has 7 children, what is the probability of their having 3 girls and then
having 4 boys?
a. 1/2
b. 1/144
c. 1/128
d. 1/256
e. none of these
5. If a couple has 7 children, what is the probability of their having 3 girls and 4
boys?
a. 1/2
b. 21/128
c. 70/128
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d. 35/128
e. none of these
6. If a couple has 7 children, what is the probability of their having 3 or more girls?
a. 35/128
b. 70/128
c. 99/128
d. 119/128
e. none of these
7. If the following cross is made: AaBbccddEe x aaBbCcDdee
>what is the probability of obtaining an individual that expresses the recessive
phenotype for all 5 loci?
a. 1/128
b. 1/64
c. 3/64
d. 9/64
e. 27/64
8. The ability to taste the compound phenylthiourea is dominant. IF both parents
are heterozygous for the taster allele (Tt), what is the probability of having a family
of 4 consisting of two tasters and two non-tasters?
a. 1/256
b. 6/256
c. 36/256
d. 54/256
e. none of these
9. In peas, tall (plant) is dominant to short, and round (seed) is dominant to
wrinkled. A plant that is heterozygous for both loci is crossed to an unknown plant.
The progeny that result are: 598 tall round: 210 tall wrinkled: 602 short round: and
198 short wrinkled. What was the phenotype of the unknown plant?
a. Tall round
b. Tall wrinkled
c. Short round
d. Short wrinkled
e. It cannot be determined
10. A tall round pea plant, when allowed to self pollinate, produces a 9:3:3:1 ratio
of tall round: tall wrinkled: short round: short wrinkled. What ratio would result if
this plant were crossed to a homozygous (true breeding) plant that was short
wrinkled?
a.
b.
c.
d.
e.
1:1: 1:1 ratio of tall round: tall wrinkled: short round: short wrinkled
1:1 ratio of tall round: tall wrinkled
3:1 ratio of tall round: short wrinkled
3:1 ratio of tall round: tall wrinkled
None of these
11. In Drosophila, yellow body (y) is sex linked and recessive. Brown eyes (bw) is
autosomal and recessive. A yellow brown male is crossed to a homozygous wildtype female producing an F1 in which both males and females are phenotypically
wild-type. The F1 are inbred to form an F2.At what frequency (of total flies) would
you expect to find a yellow (but not brown) male in the F2.
a. 1/16
b. 3/16
c. 4/16
d. 6/16
e. 9/16
12. See problem 11.At what frequency would you expect to find a yellow brown
female in the F2.
a. 1/16
b. 3/16
c. 4/16
d. 6/16
e. none of these
13. Cystic fibrosis is inherited as an autosomal recessive. Two parents without
cystic fibrosis have two children with cystic fibrosis and three children without. They
have come to you for genetic counseling. What is the numerical probability that their
next child will have cystic fibrosis?
a. 0
b. 16/128
c. 96/256
d. 1/4
e. none of these
14. See Problem 13.Their unaffected children are concerned about being
heterozygous. What is the numerical probability that a given unaffected child in the
family is heterozygous?
a. 0
b. 2/3
c. 1/3
d. 3/4
e. none of these
15. A three generation pedigree for a particular human trait is shown in the
following figure:
Y-linked can be excluded at a glance. What is the mode of
inheritance for this trait?
You may assume complete penetrance and full expressivity for the
trait.
a. X linked dominant
b. Autosomal dominant
c. X linked recessive
d. Autosomal recessive
e. either a or b
16. Mendel’s laws and where each occurs in Meiosis are as follows:
a. The principle of segregation states that two members of a gene pair
segregate from each other in the formation of gametes…demonstrated in
Anaphase 1
The principle of independent assortment states that the genes for different
traits assort independently of each other (Metaphase 1)
b. The principle of segregation states that two members of a gene pair
segregate from each other in the formation of gametes… demonstrated in
Metaphase 1
The principle of independent assortment states that the genes for different
traits assort independently of each other (anaphase 1)
c. The principle of independent assortment states that two members of a
gene pair segregate from each other in the formation of gametes…
demonstrated in Anaphase 1
The principle of segregation states that the genes for different traits assort
independently of each other (Metaphase 1)
17. Mendel’s law of independent assortment is violated by
a. nondisjunction
b. linkage
c. inversions
d. none of these
18. What year (+/- 20 years) did Mendel publish his work?
a. 1950
b. 1850
c. 1750
d. 1650
e. 1550
19. In Jimsonweed purple flowers are dominant to white. When a particular purple
flowered Jimsonweed is self-fertilized, there are 28 purple-flowered and 10 whiteflowered progeny. What proportion of the purple-flowered progeny will breed true?
a. 3/4
b. 1/2
c. 2/3
d. 1/3
e. 1/4
20. The cross of an uncertain genotype with a homozygous recessive genotype at
the same locus is a
a.
b.
c.
d.
pure breeding cross
monohybrid cross
testcross
dihybrid cross