Study problems for quiz 1
Fall 2006

Scientific Method

In each of the following examples, read the text carefully.  Then mark in the margin the location, if present,  each of the five elements of the scientific method: GOAL, MODEL(S), DATA, EVALUATION, REVISION

1. In a small town in the midwest, there is a serious problem with fly infestations from a near-by brewery. The brewery is in the habit of open-air composting of the vegetable residues from the brewing process, and flies are attracted to the mountains of rotting hops and barley scraps, where they lay eggs and their larvae develop. These flies also invade peoples' homes and are generally unpleasant. An entomologist, expert in fly control, is called in to find a means of reducing the number of flies without using pesticides. Based upon his understanding of the life cycle of the flies and their biology, he recommends that the brewery infest the compost pile with a particular type of beetle. The beetles are very good competitors, and he believes that the beetles will eat enough of the food to cause the number of flies to become tolerable.

2. “Major advances in plant breeding followed the revelation of Mendel's discovery. Breeders brought their new understanding of genetics to the traditional techniques of self-pollinating and cross-pollinating plants.  Corn breeders, particularly, tried numerous strategies to capitalize on the insights into heredity. Corn plants that had traditionally been allowed to cross-pollinate freely were artificially self-pollinated for generations and crossed to other self-pollinated lines in an effort to achieve a favorable combination of alleles. The corn we eat today is the result of decades of this strategy of self-pollination followed by cross-pollination to produce vigorous hybrid plants.”

3. “The genes of mice are remarkably similar to those of humans, despite an evolutionary distance of 75 million years between the two species. Unlike humans, however, mice are small, handy, and remarkably fecund: two months after her own birth, a female mouse can produce ten new babies. Mice live only two to three years, allowing researchers to follow disease processes from beginning to end in a relatively short time....

So it's easy to understand why mouse genes have become prize tools for finding and studying human genes, including disease genes. Scientists can also use mouse models to test drugs, devise novel therapies, and study the physiology and biochemistry of genetic diseases in ways not possible in humans.

…Despite such progress, researchers still lack animal models for most human genetic diseases. But this is changing rapidly as scientists learn that they no longer have to wait for Mother Nature to make their mutants—they can create them to order. By inserting foreign genes into animal embryos, they can produce "transgenic" animals whose cells follow the instructions of the interloper genes as well as those of their ancestral genes. The result is an explosion of new information on how genes work in specific cells and how they go about promoting health and disease in both mice and humans.”


4.  Using one activity you engage in, present an example for each of the five elements of the scientific method and consider how your use of these steps might have improved your skill.

Example:  Dr. Higgins grows tomatoes.  
Goal:  a good crop of diverse tomato varieties  
Model:  last year’s notes for which varieties grew well and produced abundant fruit
Data:  this year’s crop, particularly which varieties produced
Evaluation:  Three varieties that were successful last year failed to produce abundantly this year.  
Revision:  drop one of those varieties, change planting location for the remainder

Models

1-3.  In each of the above excerpts, find one model and classify it as “physical”, “abstract” or “sampling”.  If a model is intermediate, explain how it fits two categories.

4.  In our discussion of DNA, Dr. Higgins presented several models of this molecule.  Describe two of these models, and discuss why more than one model was used for a single subject (i.e., what different aspects of the real subject, DNA, did each of these models reveal?).

5.  Using the activity you discussed in the Scientific Method section #4, or another activity, describe three different models you employ.  If at all possible, find one example for each of the three types of models.

Example, sticking with tomatoes:  Abstract model:  what grew well last year will also do well this year.  Sampling model:  among all of the different varieties, Dr. Higgins choose 9 to plant.   Physical model:  the spots in the garden where the plants were placed this year

Genetics. 

1. A cat breeder borrows a male ("stud") to cross with her female. Both cats are dark brown. This color is known to be determined by a dominant allele at one gene. However, the breeder knows that her female also carries the allele for a recessive color, blue-grey. When the kittens are born, some of them are blue-grey and some of them are dark brown. Which of the following statements are true based upon this information?

(A) the male was homozygous for the dark brown color.
(B) the male was heterozygous and carried the recessive allele for the blue-grey color
(C) the female was heterozygous and carried the recessive allele for the blue-grey color
(D) the female was homozygous for the dark brown color
(E) about half of the kittens are blue-grey and about half of the kittens are brown
(F) about half of the kittens are homozygous blue-grey and about half are homozygous brown
(G) about 3/4 of the kittens are brown and about 1/4 are blue-grey
(H) about half of the kittens are heterozygous and have the brown color

2.  A fruit-fly geneticist has three strains of true-breeding flies (meaning that if they are always crossed within a strain, all the offspring will have the same appearance).  The first strain has twisted wings, (t), which is recessive to normal wings (T).  The second strain has yellow eyes (y) which is recessive to red eyes (Y).  The third strain is “normal”, with normal wings (T) and normal eyes (Y).  These are the Parental (P) generation.

A.  She crosses a yellow-eyed fly to a normal fly.  What do the offspring look like?  What is their genotype?  These are the F1 generation.
B.  She takes the F1 offspring from the first cross (A), and crosses them to each other.  What do these F2 offspring look like?  What are the different genotypes?  What are the frequencies of the different genotypes?

3.  The same fruit-fly geneticist now crosses a yellow-eyed fly to a twisted-wing fly (the P generation).

A.  What do the first generation offspring (F1) look like?  What is/are their genotype(s)?
B.  Taking the F1 offspring, she does a dihybrid cross.  What do the F2 offspring look like?  What are the different genotypes?  What are the expected frequencies of these different genotypes?

4.  The “central dogma” of molecular biology is gene > messenger RNA > protein.  Imagine that the enzyme synthesizing the messenger RNA makes a mistake and puts the wrong “letter” (nucleotide) base into the message. 

DNA:   TTA GCT TTC CCA CCA
mRNA: AAU CGA UUG GGC GGU

A.  what is the correct sequence for the messenger RNA?
B.  Using the genetic code, write out the correct amino acid sequence.  
C.  What is changed in the protein produced by the “mistaken” messenger RNA?

5.  Is the error described in #4 a mutation, creating a new allele?  Why or why not?