2018 Fall Semester - BIO 319 Exam 1
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1. A secondary spermatocyte has 12 chromosomes. How many chromosomes will be found in the
primary spermatocyte that gave rise to it? (2 pts)
24 (meiosis is a reductive division)
2. What are the two mechanisms that produce genetic variation in meiosis? (2 pts)
Crossing over (chiasmata ok) and random distribution of maternal and paternal chromosomes.
3. What are the building blocks of a nucleotide? With regard to the 5’ and 3’ position on a sugar
molecule, how are nucleotides linked together to form a strand of DNA? (6 pts)
The building blocks of a nucleotide are a sugar (ribose or deoxyribose), a nitrogenous base, and a
phosphate group. In a nucleotide, the phosphate is already linked to the 5¢ position on the sugar.
When two nucleotides are linked together, a phosphate on one nucleotide forms a covalent bond with
the 3¢ hyrdroxyl group on another nucleotide.
4. If the mitotic cohesin fails to form early in mitosis, how would this affect the outcome of mitosis? (6
pts)
Cohesin is needed to hold the sister chromatids together until anaphase of mitosis and if this fails to
form, the sister chromatids could separate before anaphase and as a result, chromosomes would not
segregate properly to daughter cells.
5. Explain the relationship between gene and trait (4 pts).
A gene is a segment of DNA. For most genes, the expression of the gene results in the production of a
functional protein. The functioning of proteins within living cells affects the traits of an organism.
PG 1 TOTAL POINT (________out of 20)
2018 Fall Semester - BIO 319 Exam 1
NAME________________________________
UB ID # _______________________________
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6. What is Mendel’s law of segregation? Why is it important? How does it refute the “blending
mechanism of heredity”? (6 pts)
a) Mendel’s law of segregation states that an organism possesses 2 alleles for any particular
characteristic. These alleles separate in the formation of gametes. In other words, 1 allele goes
into each gamete.
b) This law is important because it explains how the genotype ratio in the haploid gametes are
produced.
c) It refuted the blending mechanism theory because the F1 generation showed only 1 of the 2
parental traits (not a mix of both traits or intermediate of both traits).
7. From Mendel’s work, when the two factors of a single character are different and present in the same
organism, one variant is ___ dominant__and its effect can be seen, the other variant is _ recessive_ and
is not seen. (4 pts)
8. A man who has the recessive X-linked trait hemophilia is married to a woman with no family history of
hemophilia. Draw a Punnett square showing the genotypes of the parental gametes and their
potential offspring. Be sure to indicate the sexes of the offspring, which ones will have hemophilia,
and which ones are carriers. Use H to designate the normal allele and h for the allele that causes
hemophilia. (6 pts)
Six points total
One point each for:
Male gametes are Xh and Y
Female gametes are XH and XH
Offspring are XH Xh and XH Y (If the parental genotypes are wrong, student should have the correct
offspring for that incorrect parental genotype.)
XH Y are male and XH Xh are female
No offspring are affected.
XH Xh is a carrier
PG 2 TOTAL POINT (________out of 16)
2018 Fall Semester - BIO 319 Exam 1
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9. In the California poppy, an allele for yellow flowers (C) is dominant over an allele for white flowers (c).
At an independently assorting locus, an allele for entire petals (F) is dominant over an allele for fringed
petals (f). A plant that is homozygous for yellow and entire petals is crossed with a plant that is white
and fringed. A resulting F1 plant is then crossed with a plant that is white and fringed, and the
following progeny are produced:
54 yellow and entire
58 yellow and fringed
53 white and entire
10 white and fringed
Please answer the following questions:
a) Formulate a hypothesis that you think is consistent with the observed data (4 pts)
b) Use a chi square test to compare the observed numbers with those expected for the cross. A chisquare table is provided below (4 pts)
c) What conclusion can you make from the results of the chi-square test? Suggest an explanation for
the results. (4 pts)
a) This is basically a test cross and provided that Mendel’s law indicating that genes assort
independently, you should obtain a phenotypic ratio of 1:1:1:1 for the different phenotypic classes.
b) Chi square value should be 35 with df = 3. Null hypothesis rejected.
c) From the chi-square value, it is unlikely that chance produced the differences between the
observed and expected ratios, given that the number of plants with the ccff genotype is fewer than
expected, a more plausible explanation is that the ccff genotype had a lower survival rate /less
viable than other genotypes (see lecture #6)
PG 3 TOTAL POINT (________out of 12)
2018 Fall Semester - BIO 319 Exam 1
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10. Describe how two linked genes are arranged relative to one another in the genome. How does being
linked affect the assortment of these two genes in a cross? (4 pts)
Linked genes are close to one another on the same chromosome. (2 points)
Linkage greatly reduces the independent assortment of two genes. (2 points)
11. Two different strains of sweet peas are true-breeding and have white flowers. When plants of these
two strains are crossed, the F1 offspring all have purple flowers. What is this phenomenon? (2 pts)
Complementation (you will not receive partial credit for wrong word usage, you will receive partial or
full credit for spelling errors (depending on the error) that is close to the word)
12. For each of the following pedigrees, which term best fits the inheritance pattern: X-linked recessive,
autosomal recessive, or autosomal dominant. Circles are females, squares are males, and affected
individuals are filled in. Heterozygotes are not indicated (2 pts each; 4 pts total).
Autosomal dominant (2)
X-linked recessive (2)
13. What does it mean for a trait to be polygenic? Why are most traits polygenic? (2 pts ea; 4 pts total)
A polygenic trait is determined by more than one gene. (2)
Most traits that are recognizable at the organismal level arise from complex developmental programs and hence
are influenced by multiple genes. (2)
PG 4 TOTAL POINT (________out of 14)
2018 Fall Semester - BIO 319 Exam 1
NAME________________________________
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14. A female fly with a gray body and long bristles (e+e s+s) is crossed to a male fly with an ebony body and
short bristles (ee ss). The progeny obtained are described in the chart below. Calculate the distance
between the ebony (e+) and short (s+) genes. Show your calculations for full credit. (6 pts)
Gray body, Long bristles
Ebony body, Short bristles
Gray body, Short bristles
Ebony body, Long bristles
220
230
22
28
Recombinants = 22 + 28 = 50
[2 points]
Total number of flies = 220 + 230 + 22 + 28 = 500 [1 point]
Map units = (recombinants / total ) X 100 = 50/500 X 100 = 10 map units (or cM/centiMorgans)
1 point for correct formula
1 point for answer
1 point for using correct units
15. When does the erasure and reestablishment phase of genomic imprinting occur? Explain why it is
necessary to erase an imprint and then reestablish it in order to always maintain imprinting from the
same sex of parent (6 pts)
Erasure and reestablishment of the imprint occurs during gametogenesis (2 pts)
It is necessary to erase and reestablish the imprint in germ cells so that each sex will transmit
only a single type of allele (inactive or active). In somatic cells, the two alleles for a gene are
imprinted differently, according to the se of the parent from which the allele was inherited. (4
pts)
16. What are the three molecular mechanisms by which a mutant allele be dominant over a wild-type
allele? (6 pts)
Gain of function, dominant negative, and haploinsufficiency (2 pts each)
PG 5 TOTAL POINT (________out of 18)
2018 Fall Semester - BIO 319 Exam 1
NAME________________________________
UB ID # _______________________________
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17. Hemophilia is an X-linked recessive trait in humans. If a heterozygous woman has children with an
unaffected man, what is the probability that she will have two affected offspring out of five (8 pts)
First set up the punnet square:
Male gametes are XH and Y
Female gametes are XH and Xh
Offspring are XH XH , XH Y, Xh Y and XH Xh. There is a 0.25 probability of each type of offspring.
Set up bionomial expansion equation – X =2, n=5, p = 0.25, q=0.75, you will get 0.26 or 26% of the
time.
18. How is the phenomenon of cytoplasmic inheritance deviate from Mendel’s inheritance pattern? (4 pts)
Mendel’s inheritance pattern stated that 2 copies of a gene segregate from each other during
transmission from parent to offspring, for mitochondrial genes, there are not 2 copies – maternal
mitochondrial genes are transmitted to offspring but paternal mitochondrial genes are not.
19. Fruit flies with scarlet or cinnabar mutations have bright red eyes because they cannot synthesize
brown pigment. Fruit flies homozygous for brown or purple mutations have brownish-purple eyes
because they cannot synthesize red pigment. Fruit flies homozygous for the white mutation have
white eyes because they cannot transport the red and brown pigments into the eye.
Is the purple mutation epistatic to the brown mutation? Why? ( 8 pts)
Yes (3 pts), the purple mutation masks the brown mutation, resulting in the white eye and not red eyes.
That’s because in the absence of purple gene, no red pigment will be made regardless of whether brown
gene makes functional gene product or not (5 pts)
PG 6 TOTAL POINT (________out of 20)