Exam 4 Review Answers
Supplemental Instruction
IowaStateUniversity / Leader: / Matt C.
Course: / Biol/Gen 313
Instructor: / Dr. Rodermel
Date: / 12/07/2017

Introduction: The material on this exam is from chapters 2, 3, 12, and 14.

Multiple Choice

  1. Which of these is an epigenetic modification?
  2. Cytosine methylation
  3. Histone lysine acetylation
  4. Moving histones along the DNA
  5. Histone lysine methylation
  6. All of the above

Yep. All of these are epigenetic modifications.

  1. During which phase of mitosis does the nuclear envelope break down?

  1. Prophase
  2. Metaphase
  3. Anaphase
  4. Telophase
  5. Interphase

Yep, this happens during prophase.

  1. How does a eukaryote initiate translation?
  2. The ribosome recognizes the Shine-Dalgarno sequence.
  3. The ribosome recognizes a Shine-Dalgarno-like sequence.
  4. The ribosome recognizes several initiation consensus sequences at the same time.
  5. The ribosome scans for astart codon embedded in the Kozak sequence.
  6. None of the above

Lots of definitions so far.

  1. You are working with two unlinked genes in Drosophila melanogaster. The first controls body type and has two alleles. Dominant E produces normal body color while recessive e produces ebony body color. The second controls eye color and also has two alleles. Red eyes arise from the dominant allele R, while sepia eyes arise from the recessive allele r. You testcross a female fly with red eyes and normal body color and observe the following offspring counts. What is the female’s genotype?

Red and normal / Red and ebony / Sepia and normal / Sepia and ebony
93 / 0 / 105 / 0
  1. EE RR
  2. Ee RR
  3. Ee Rr
  4. EE Rr
  5. None of the above

There are no ebony offspring, so the female must have been homozygous for normal body color. There is an approximately even split between red and sepia eyes, so the female must have been heterozygous for the eye color allele.

  1. Consider the following. You perform a cross of a plant that produces striped squash and one that produces yellow squash. After observing the offspring as described below, what do you propose to be the genotypes of the parents?
White / Striped / Yellow
0 / 12 / 16
  1. ww yy x ww yy
  2. Ww yy x WW Yy
  3. Ww yy x Ww Yy
  4. ww yy x ww YY
  5. None of these

The correct cross should be ww Yy x ww yy.

  1. When does crossing over occur normally?
  2. During mitotic prophase
  3. During prophase I
  4. During prophase II
  5. During metaphase I
  6. This doesn’t happen in eukaryotes
  1. In which of the following is a lariat structure formed?

  1. Poly-adenylation
  2. Splicing
  3. Telomere lengthening
  4. Attenuation
  5. None of these

The point of this question is to point out that mRNA processing is a step in expression control.

  1. In Arabidopsis thaliana, sequence R is involved in the activation of the localized sequences K and H. Sequence U exhibits identical response elements to K and H, but is acted on by the intervening effect of sequence T and is instead only activated by another sequence R that is further downstream. What is sequence T an example of?
  2. Regulatory gene for an activator
  3. Regulatory gene for a repressor
  4. Enhancer
  5. Insulator
  6. Response element

R is an enhancer. K, H, and U are just genes under the control of the same response elements. T is an insulator.

  1. A single type of signal molecule enters the nucleus of a eukaryotic cell and induces transcription in multiple genes. How does this most likely happen?
  2. The genes are linked on an operon.
  3. Signal integration occurred and expanded the downstream signal.
  4. A first gene was activated by the signal directly and was transcribed, translated, and the resulting product activated the other genes.
  5. The activated genes share response elements.
  6. None of the above.

It’s even likely that signal integration will occur at some point, but this doesn’t explain why multiple genes would transcribe at the same time.

  1. Which of the following describes a microsatellite?
  2. Short, non-coding DNA just outside of a coding sequence.
  3. Short DNA strings that are repeated at random one after another.
  4. Single-nucleotide polymorphisms (SNPs) used in identification of gene alleles.
  5. Small, circularized eukaryotic DNA found in mitochondria or other prokaryote-derived organelles.
  6. Multiple of the above are true.
  1. In fruit flies, antennapedia is dominant over normal antenna and normal body color is dominant over albinism. Both traits are autosomal. What will be the phenotypic ratio for the F2 generation if you cross a true-breeding female with antennapedia and albinism with a true-breeding male for normal antennae and body color for the parental cross (P)?
  2. 1:1:1:1
  3. 4:2:2:2:2:1:1:1:1
  4. 9:3:3:1
  5. 1:1
  6. You can’t tell from the information given.

As a hint, 90% of the time that you’re asked for the F2 phenotype without being provided with the F1 and there are two genes being considered, the answer will be this.

  1. Brown eyes are dominant over green eyes. If one parent has brown eyes and the other has green eyes, what would giving birth to a green-eyed child indicate about the parents?
  2. The green-eyed parent is homozygous.
  3. The brown-eyed parent is homozygous.
  4. The green-eyed parent is heterozygous.
  5. The brown-eyed parent is heterozygous.
  6. The child couldn’t have green eyes from the above scenario.

Assume B is the allele for brown eyes and b for green eyes. Bb x bb can result in a bb offspring. Also, the green-eyed parent is homozygous recessive based on their phenotype.

  1. Observe the following capillary gel readout of microsatellites. If the two sequences around 180 bp (D8S1179) represent homozygotes – indicating the level of baseline justification to call a homozygote sequence as opposed to a heterozygote – how many heterozygous sequences are lost upon conversion to cancerous tissue?

  1. None.
  2. 1
  3. 2
  4. 3
  5. This can’t be determined.

D5S1462 and D3S1763 are converted from heterozygotes to homozygotes.

  1. Which of these components of the basal transcription apparatus receives signals from activators and repressors to either begin or prevent transcription initiation in eukaryotes?
  2. RNA polymerase II
  3. Transcription factors
  4. Enhancer/silencer
  5. Mediator
  6. None of the above
  1. Consider the diagram below. This cell is from a diploid organism with 4 chromosomes and is undergoing replication. What stage in replication is this?

  1. Metaphase.
  2. Metaphase I.
  3. Metaphase II.
  4. Multiple of the above could be represented by this diagram.
  5. None of the above.

The tetrads are lined up, so this must be Metaphase I.

  1. What is the term for a different form of a gene?

  1. Trait
  2. Characteristic
  3. Allele
  4. Genotypic polymorphism
  5. None of the these

  1. When does synapsis and crossing over occur during meiosis?

  1. Prophase I.
  2. Anaphase I.
  3. Prophase II.
  4. Anaphase II.
  5. Multiple of these.

  1. In a certain organism, a homozygous recessive allele is embryo lethal. No offspring with the homozygous recessive allele will be born. If you cross two heterozygous individuals, what will be the expected genotypic ratio of the surviving offspring?
  2. 1:1
  3. 1:2
  4. 1:3
  5. 1:2:1
  6. None of the above.

This is because the other 1 died off. 1:2:1 loses the second one. Leaves you at 1:2.

  1. Consider the following cross. What is the likelihood of observing an XXyyZz genotype?

XXYyzz x XxYyZz

  1. 0
  2. 1/4
  3. 1/8
  4. 1/16
  5. 1/32

There is a 50% chance that XX will arise. There’s a 25% chance of yy. There’s a 50% chance of Zz. Multiply these together and the result is 1/16.

  1. A certain diploid organism has 10 chromosomes in its somatic cells. How many DNA molecules will be present in the cell during anaphase II?

  1. 40
  2. 20
  3. 10
  4. 5
  5. None of the above.

  1. A and B are dominant, independently segregating alleles. An individual with the genotype Aabb is crossed with an individual of unknown genotype. If the following phenotypes are observed, what is the genotype of the second parent?

AB / Ab / aB / ab
272 / 0 / 88 / 0
  1. AABB
  2. AaBB
  3. AABb
  4. AaBb
  5. This can’t be determined.

The other individual must be homozygous for B since no b offspring are born. From there, there is approximately a 3:1 ratio of A to a. This indicates that Aa must be last genotype.

  1. A certain individual expresses the dominant phenotypes A, B, C, and D. If this individual is testcrossed, what phenotypic ratio would you expect of the offspring if the genotype of the parent is AABBCcDd?
  2. 1:1
  3. 1:2:1
  4. 1:1:1
  5. 1:2:2:1
  6. 1:1:1:1

There will be a 1:1 ratio of C to c and another 1:1 ratio of D to d. These will then be randomly mixed, making a 1:1:1:1 phenotypic ratio.