Dr. Reichler’s Bio 212  1-2pm        Print Name:_______KEY_____________
Exam #4   December 11, 2002

    Answer each question as succinctly as possible in the space provided.  If needed, continue on the back.  If you use a drawing as part of your answer, be sure to also include a written explanation.  Read each question carefully and don’t hesitate to ask if a question seems unclear.  These questions have specific answers, although for some, more than one answer is possible.  To receive full credit you must clearly and fully answer the question being asked.  Each question is worth 6 pts, unless otherwise noted, for a total of 100 points possible for this exam.

1. a.  Propose a hypothesis to answer the following question:  Why is sexual reproduction prevalent in multicellular organisms?
It must be advantageous in some way.  The two most obvious advantages are:
Increases genetic diversity.
Provides two copies of each gene to cover any errors/mutations that may be inherited.

b. Design an experiment to disprove your hypothesis.
For either.  A population of asexual and sexually reproducing individuals can be monitored to determine which survives better.

2. a.  What is the basic connection between genotype and phenotype?  (4 pts)
genotypes are the genes that when expressed give rise to traits=phenotypes.

b. What are two issues that can complicate the relationship between genotype and phenotype? (8 pts)
Any two of:
Multiple genes can code for a single phenotype.  One gene may effect many phenotypes.  The environment plays a role in determining the expression of genes which effects how those genes are expressed as phenotypes.

These questions refer to studying an organism called a “Snuffleupagus”.  Snuffleupagi have one gene that codes for body color (the alleles are designated: G=green and P=purple) and another that codes for whether they are furry or bald (the alleles are designated: F=furry and B=bald).  Note:  To receive partial credit, show your work where appropriate.  Each numbered question is a self-contained situation.  Assumptions for one numbered question are separate for the other questions.

3. a.  One Snuffleupagus , named Fred, is green and bald.  Both parents are homozygous for color and hair.  His father is green and furry, his mother is purple and bald.  For the color and hair genes, which allele is dominant and which is recessive?
Green Dominant
Bald Dominant

b. If the genes for color and hair are on the same chromosome, but Fred does not have recombination, what are the possible genotypes Fred’s gametes can have?
GF or PB

4. a.  Another Snuffleupagus, Sally is green and has the genotype GP, her mate Frank is purple with the genotype PP.  What percent of their offspring will be green or purple?
50% green, 50% purple

b. If the hair gene is sex-linked with the bald allele dominant, and Sally (female) is furry while Frank (male) is bald, how will the furry or bald trait be expressed differently in male and female offspring?
All males furry, All female bald

5. a.  A new generation of Snuffleupagi are born and surprisingly some of these offspring are orange (this allele is designated: O=orange).  There have never been orange Snuffleupagi before.  How could this new color have arisen?
Mutations in the gene for color have given rise to a new gene for a new phenotype.

b. Rachel with the genotype GO and Fritz with the genotype GP mate and have 50% green and 50% orange offspring.  What are the dominant and recessive alleles for color?
Orange is dominant over Green, Green is dominant over Purple.

6. In another group of Snuffleupagi, some bald and furry individuals are mating and having offspring that are thinly covered in fur.  How can this be explained?
Either:  incomplete or co-dominance is causing the heterozygous individuals to have different phenotype/ traits than the homozygous individuals.

7. a.  In Snuffleupagi there is a gene that codes for the diameter of the eyes.  Very large-eyed Snuffleupagi cannot see well, nor can very small-eyed ones.  What size eyes would you expect to find in Snuffleupagi?  Explain.
Medium-sized eyes.  The large and small eyed would be selected against because they can not see well, and the medium-sized eyed ones would be able to reproduce and pass on the genes for medium sized eyes.

b. What kind of selection is this?  Explain.
Stabilizing selection.  Genetic variation is being reduced, the middle of the range of traits is advantageous/ being passed on.

8. a.  If as one looks at the fossil record of Snuffleupagi, you notice that Snuffleupagi are twice as large currently as they were 1000 years ago, what type of selection is this?  Explain.
Directional selection.  Larger size is advantageous and can reproduce more than smaller ones.  The genotype/phenotype is changing toward larger size.

b. Would the answer in 8a be different if Snuffleupagi only reproduce once every 500 years?  Why or why not?
Yes, with so little reproduction, there is not likely to be much selection.  So the difference is likely due to environmental effects.

9. Are humans evolving?  Explain.  (10 pts)
Two conditions need to be met for natural selection to take place…genetic diversity and limited reproductive success.  Yes, there is definitely genetic diversity.  But even though we have reduced the selection for whom can reproduce and not, there are still limits on human reproductive success.  Several genetic diseases and other factors mean that not everyone can or does reproduce.