In compliance with the Dartmouth honor principle, all the work you hand in on this exam is to be your own. Please remember to be precise in your wording – scientific descriptions rely on accurate use of specific terms. Also, try to keep your answers concise. If you can say something briefly there is no need to create a lengthy answer just to fill up space. Use the space provided and the point values for each question as indicators of the amount of detail your answer should contain. If you really need extra space for an answer, turn the page over and continue your answer on the back of the same piece of paper. To facilitate grading, we separate the exam by page; if your answer is on a different sheet of paper we will not see it. Please put your name on each page now.

If something is not clear to you, please ask me during the exam. That is why I stay in the room. Good luck.

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

The trait is recessive because individuals not showing the trait (I-1 or I-2) can have offspring that do show the trait (II-4, II-6). If the trait were dominant then at least one of the parents would also show the trait

b. For each of the following individuals, indicate the genotype (specify the two alleles for each individual) and briefly explain your answer. 2 points each

I-1: Aa - doesn't show trait so is not aa. Passes on trait so must contain `a'.

II-3: Aa - doesn't show trait so is not aa. Passes on trait so must contain `a'.

II-4: aa - shows the recessive trait

II-7: AA - likely to be true because none of her 8 children had the trait even though here husband did

III-7: Aa - doesn't show trait so is not aa. Passes on trait so must contain `a'.

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 round and green (2 points). (Y = yellow/green; R = round/wrinkled)

Round is dominant so RR or Rr will be round. Green is recessive, so only yy is green. The round/green peas are highlighted in gray - 3/16 of offspring will be round and green

4. Explain why a trait like intelligence is not inherited in a Mendelian fashion. (5 points)

Intelligence involves many different genes interacting in the context of all the other genes in the individual. Since many genes are involved (it is a polygenic trait), simple Mendelian inheritance is not observed.

5. In mitosis, the chromatin condenses into metaphase chromosomes before cell division. Why is this a necessary step (i.e. - what would happen if the chromatin did not condense?)? (5 points)

If cell division was attempted without condensing all the chromatin into chromosomes, the chromatin fibers would be too tangled to separate evenly (if at all). The forces pulling the intertwined chromatin fibers apart would either tear the fibers or not be able to separate them. This would result in the daughter cells getting different sets of DNA, probably missing certain genes in one or the other daughter cell.

6. During development, both growth and differentiation are important. Define what is meant by these terms. (4 points)

Growth is the process by which the size of a tissue gets bigger. This is through increases in cell number brought about by cell division.

Differentiation is the process by which cells become more specialized. They acquire the ability to perform new tasks (e.g. sense light, contract).

7. Explain what is meant by contact inhibition and describe how it relates to cancer cells. (5 points)

Contact inhibition is the cessation of cell growth and division when the cell contacts a neighboring cell. The contact with the neighboring cell actually inhibits continued cell division. Cancer cells do not obey contact inhibition and therefore continue to grow even though they are in contact with other cells - this results in a tumor.

8. Explain (or diagram) how the secondary structure of an RNA (the way it forms regions of intrastrand base pairing) can influence the level of expression of different coding regions on the same polycistronic mRNA. (5 points)

Each coding region has a start signal at which the ribosome can bind and initiate protein synthesis. If the basepairing of the mRNA is such that one of the start signals is participating in basepairing, then that particular start signal will not be available to the ribosomes and that particular coding region will not be translated.

9. In eukaryotic organisms, cells often have to synthesize proteins that are secreted from the cell. These proteins follow a defined pathway through the cell. Describe an experiment that was done to elucidate that pathway. (8 points)

This was done using a pulse-chase experiment. Cells were labeled using radioactive amino acids as precursors to proteins for a short time (the pulse) and then transferred to growth medium without any radioactive amino acids (the chase period). At various times after the pulse, cells were examined to determine the location of the radioactive proteins which were synthesized during the pulse. It was found that the proteins initially were localized in the endoplasmic reticulum, but then with increasing time migrated to the Golgi complex and eventually through vesicles and out of the cell.

10. Only one third of the mass of chromatin is DNA. What makes up the other two thirds? (4 points)

The other two thirds of the mass is protein, equal amounts of histones and non-histone proteins. [the ratio of DNA:histone:non-histone = 1:1:1]

11. Name the three major kinds of RNA and briefly explain their roles in protein synthesis. (6 points)

rRNA: interacts with ribosomal proteins to form ribosomes, which are the main catalyst in protein synthesis

mRNA: contains the genetic information used by the ribosome to synthesize a protein

tRNAs: bring amino acids to the ribosome in the order specified by the mRNA.

12. What would be the effect on gene expression in a prokaryotic cell if there were a mutation in the gene coding for sigma factor such that the mutant sigma factor could no longer interact with the core RNA polymerase? (5 points)

If sigma factor could not bind to the core RNA polymerase, it would not be possible to have initiation of transcription. All transcription of specific genes would be turned off.

13. Meselson and Stahl used DNA labeled with heavy nitrogen to follow DNA replication. Diagram what they would have seen if replication were conservative instead of semiconservative. Show results after one round of replication and after two rounds of replication. You can use a labeled diagram if you want. (8 points)

initial DNA is: H:H

after one generation of conservative replication: H:H and L:L

after two generations of conservative replication: H:H and L:L and L:L and L:L

14. Describe Griffith's experiments that demonstrated the presence of a transforming principle in pneumonia bacteria. (10 points)

injected rats with smooth bacteria -> they died

injected rats with rough bacteria -> they lived

heated smooth bacteria then injected into rats -> rats lived

mixed heated smooth and then mixed with rough and injected -> rats died

Griffith deduced that something was transferred from the components of the killed smooth cells to the rough cells to change the rough cell's behavior. He called this unknown material that was transferred a transforming principle.