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1. Pedigree diagrams are often used to illustrate the inheritance of specific human traits. Using the pedigree diagram shown here, answer the following questions. For this question assume that the dominant allele is indicated by A and the recessive allele is indicated by a.
a. Is the trait in the pedigree a dominant or a recessive trait? Explain your answer. (3 points)
recessive - because it is not seen in the parents (I) but IS seen in the offspring (II)
b. For each of the following individuals, indicate the most likely genotype (specify the two alleles for each individual) and briefly explain your answer. (2 points each)
2. Identify the following components of the cell in the diagram shown below: nucleus, nucleolus, Golgi complex, rough endoplasmic reticulum, a mitochondrion, and chromatin. Please be careful where you place your lines - be precise. (12 points)
3. Mendel performed a series of dihybrid crosses and determined that the traits he was studying were inherited independently. Fill in the Punnett square shown here (8 points) and state the fraction of offspring that will be wrinkled and tall (2 points). (T = tall/short; R = round/wrinkled)
fraction that are wrinkled and tall = 3/16
4. What does the term "polygenic inheritance" mean? (2 points) Give an example of a trait that is polygenic. (2 points)
polygenic inheritance means that the trait being discused does not depend on a single gene -- rather, it is due to the products of multiple genes. Examples include height, intelligence, shape of nose, smiles/hour, etc.
5. Briefly describe the following stages of mitosis: interphase, prophase, metaphase, anaphase, and telophase. (2 points each)
interphase: chromatin is decondensed, nuclear envelope intact, much transcription
prophase: nuclear envelope dissolves and chromosomes begin to condense, spindle begins to form
metaphase: chromosomes maximally condensed, aligned on metaphase plate, spindle fibers attach to chromosomes (at centromeres)
anaphase: chromosomes migrate to poles of cell, cell elongates
telophase: chromosomes begin to decondense, nuclear envelope reforms, spindle disappears, cell actually begins to pinch in two (animals) or be divided by a plate (plant)
6. In an attempt to learn about how the cell cycle is regulated you do a cell fusion experiment in which you take cells in G1 phase and fuse them with cells in mitosis. This process is like combining two soap bubbles into a single bubble - the contents are mixed. In the resulting fused cells, you find that the nuclear envelopes of the G1 cells break down and the G1 cell chromosomes condense. What does this suggest in terms of factors that are involved in cell cycle regulation? Explain your answer. (5 points)
This suggests that there is some diffusible factor present in the mitotic cell that causes the G1 cell contents to behave as if they were in mitosis - causing the nuclear envelope to break down and the chromosomes to condense.
7. It is known that all cells in a multicellular organism contain a complete set of genetic information for that organism. Give a recent example of how we know this to be true. Explain your answer. (5 points)
Cloning of Dolly the sheep or, more recently, cloning of cows for "pharming" illustrates this. In each case, a nucleus from a mature non-germline cell was transferred into an egg cell. This egg cell was capable of creating an entire new organism based on the DNA information in the nucleus from the adult cell. Other answers are also possible
8. The shape of a protein molecule directly influences its function. Changes in the shape of a protein are often used to send a signal or do some work. Give one example from our lectures in which the change in shape of a protein is important. (3 points)
Several examples were discussed including: rhodopsin changing shape from light and causing an electrical signal, myosin changing shape to interact with actin and produce force, sigma factor interacting with core RNA polymerase to promote initiation of transcription, rho factor interacting with core RNA polymerase to promote termination of transcription, and others.
9. What is a peptide bond? (3 points)
it is the bond that is formed between two adjacent amino acids in a peptide chain.
10. Recently, there have been news reports about an "immortality gene" which has just been isolated. We (in Bio 4) know that this is in fact a telomerase gene. With what we have gone over in class, describe (a) what is a telomere? (2 points), (b) what is the function of telomerase? (2 points), and (c) why might telomerase be considered an immortality gene? (6 points)
a) a telomere is the DNA that resides at the end of a chromosome
b) telomerase functions by filling in any remaining single stranded ends after DNA replication. These single stranded ends result from the removal of an RNA primer that was used to initiate the DNA chain at the very end of the DNA.
c) telomerase is normally inactive in somatic cells. Therefore, we lose a little of our genome from the ends of each chromosome with each DNA replication. After 50-100 divisions, the cells are no longer capable of dividing because so much of the DNA is lost. In germ line cells, telomerase is active and no DNA is lost from chromosome ends. Scientists have recently found that by turning on the telomerase gene in normal somatic cells, the ends of the chromosomal DNAs are restored and the cells appear to divide indefinitely - i.e. they are imortal.
11. Describe the Hershey-Chase experiments which determined that DNA is the genetic material and not protein as shown by studying phage infections. (8 points)
12. Approximately what fraction of the mass of chromatin is comprised of DNA? (2 points)
13. During DNA replication, each newly synthesized DNA fragment is started with a small RNA primer. Why is it thought that RNA is used as a primer rather than DNA? (4 points)
Because RNA is synthesized by a primase without error-checking it is not as accurate as the normal DNA, which is synthesized with error-checking. Thus the RNA can be recognized as less accurate and can be removed and replaced by DNA later in replication. If the primer was DNA, there would be no way to tell accurate from inaccurate DNA.
14. Explain the role of s-factor (sigma factor) in initiation of transcription in prokaryotes -- you can use a labeled diagram if you wish. (4 points)
Sigma interacts with the core RNA polymerase to enable the core to initiate transcription. Without sigma factor bound, the core RNA polymerase is not very efficient at recognizing promoters.
15. What is a polycistronic mRNA? -- you can use a labeled diagram if you wish (3 points)
It is a mRNA that has several coding regions on it. Each coding region has its own start and stop codon.
16. tRNAs are intimately involved in protein synthesis. All tRNAs share some common characteristics, yet they all must be distinct. Name one reason why all tRNAs must be similar. Name one reason why each tRNA must be distinct. (4 points)
All tRNAs must be similar because they must all fit into the pockets in the ribosome.
All tRNAs must be different because they each carry a different amino acid.
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