Midterm I, BIO 350

                                              Darwinian Medicine

                                              November 1, 2001

NAME  KEY                            

 

            Print your name legibly at the top of each page and be sure your test has 7 pages.  Work through the test as rapidly as possible, answering the easiest questions first, and then return to more difficult ones.  Read each question carefully and completely, and think about your answer before starting to answer.  If necessary, use the back of the page to make notes or organize your answer.  Do not hesitate to ask for clarification if you are unsure about the meaning of a question.  Print your answers neatly in the space provided, using proper sentences.  Illegible and incomprehensible answers will not receive credit.  Reread the questions and your answers before turning in your paper to be sure each answer is complete and to the point.  The number of points possible is shown in parentheses after the number of the question.  The test ends at 2:10 pm. 

 

1. (20) A. What is the disadvantage of the phenotype produced by the HbSHbS homozygote for the sickle allele of the  -globin gene?

 

Individuals with this phenotype have sickle-cell anemia and     

virtually no Darwinian fitness because they are weak and usually

die early in life. (5 pt.)                                       

 

B. What is the disadvantage of the phenotype produced by the HbAHbA homozygote for the normal allele of the  -globin gene?

 

This phenotype is susceptible to malaria, and individuals with  

this phenotype may be weakened or die of malaria, reducing their

Darwinian fitness. (5 pt.)                                      

 

C. Why can the frequency of the sickle allele (HbS) never exceed p = 0.50 (= 50%)?

                  Since the HbS HbS homozygote has essentially no

Darwinian fitness, the only source of HbS alleles for the next

generation is from heterozygote parents, in which only one half 

of the  -globin alleles are HbS.  Since HbAHbA homozygotes may not

be eliminated by malaria, reproduction by surviving HbAHbA       

and HbS HbA individuals cannot produce > 50% HbS alleles. (5 pt.)

D. Name a region or country in which the sickle allele (HbS) occurs at a high frequency.  If possible, name the country or region in which it reaches the highest frequency.

 

    India (highest), Africa, Mediterranean, Middle East  (5 pt.)

2. (18) Darwin knew that natural populations tend to have a stable number of individuals even though all species have the potential to grow exponentially.  A. What was the evidence that all species have the potential to grow exponentially?

 

Females of every species can produce enough offspring to more   

than replace themselves and their mate.  Thus, their population

could increase by a constant percentage each generation (i.e.,  

grow exponentially).  (6 pt.)

B. Why do natural populations usually not grow exponentially?

 

Many offspring produced fail to survive long enough to reproduce

or they fail to reproduce.  (6 pt.)

                                                                

 

C. What role did Darwin’s realization that all natural populations tend to have a stable number of individuals even though they have the potential for exponential growth play in his development of natural selection?

                                 The greater the proportion of   

offspring that fail to survive and reproduce, the greater the 

potential for differences in the rates of survival and reproduc-

tion by different phenotypes to produce selection. (6 pt.)

                                                                

 

3. (18) The enzyme lactase is secreted late in life by some humans.  A. What is the normal function and timing of lactase secretion in mammals other than humans?

 

 The normal function of lactase is to catalyze the split of lactose into glucose and galactose in      the intestine of the nursing offspring. (6 pt.)

                                                                                                                                                      

 

B. What has selected for extension of lactase secretion into adulthood in humans?   Consumption of raw milk as regular food by adults.  (6 pt.)

                                                                                                                                                      

 

C. How does this constitute evidence that we are more than just “stone agers in the fast lane?”

 

The practice of herding dairy cattle and consuming their milk is a post-stone age practice.         

Evolution of the ability by adults to digest lactose in milk must be a post-stone age adaptation.

 (6 pt.)                                                                                                                                    

 

                                                                

 

 

4. (16) Below is a cladogram for four species and showing four characters (A-D).  Assuming that the structure of the tree is correct and that parsimony provides the best explanation for the distribution of character states among species, answer the questions below.

 

 

 

 

Spp.  1              2              3             4               5

     ABCD’   ABCD’   AB’C’D   AB’C’D   AB’CD’   A. Indicate on the cladogram where

          .              .               .               .               .                      character C’ evolved by drawing a

            .          .                    .         .              .              line across the appropriate segment.

               .    .                         .     .            .                              and labeling it “C’.”                  

                 .                              .            .                                 

                       .                 C’ ---.---  .      (4 pt.)                       B. Which character tells us nothing

                              .                      .                                          about relationships among the

                                    .          .                                                species?  (Circle one.)

                                         .                                                                 

                                Ancestor (ABCD)                                                A     B     C     D    (4 pt.)

 

C.  Suppose that Species 1 is Homo sapiens and D’ is susceptibility to a disease (e.g., rickets).  Why would Species 2 be a better model in which to study the disease than Species 5?

 

D’ is shared by Species 1 (Homo sapiens) and Species 2 because their common ancestor had it.    In contrast, Species 5 has evolved D’ independently.  Thus, it is more likely that D’ in Species 1

& 2 is the same in those two species than in Species 1 & 5.     (4 pt.)                                            

D. Why would it be a mistake to make a genus that included species 1, 3, and 5?

 

Because it would constitute a genus with species that are more closely related to other species    

outside the genus than they are to each other.  (All members of a taxon should be more closely  

related to each other than to any species outside the taxon.)     (4 pt.)                                          

5. (5) The major point of Chapter 8 (Revolution) of The Coming Plague was that:

a. cancer is caused simply by environmental factors.

b. cancer is often infectious, caused by “slow” visuses.

c. molecular biology received all the money from federal agencies, crowding out the study of infectious diseases.

d. retroviruses like HTLV-1 effect the immune response.

e. None of the above.

 

6. (5) The Ebola outbreak at Yambuku was stopped by the actions of :

a. Joe McCormick and the other experts from the United States and Europe.

b. the local villagers.

c. nobody; it just died out.

d. the nurses at the local hospital.

e. None of the above.

 

 

7. (16) Describe three lines of evidence that having darkly pigmented skin increases Darwinian fitness of humans living in hot climates.

 

A. There are many lines of evidence.  Darkly pigmented skin has   evolved more than once (clearly in Panama) in warm climates. /

Albino black Africans have very high rates of skin cancer. /    

Whites in warmer climates have elevated rates of skin cancer. /

Exposure to excessive sun light causes damage to skin and       

increases the probability of skin cancer later in life. / Dark

pigmentation occurs in many species from warm climates./         

   Solar radiation generally damages cells. (4 pt. ea.)

B.                                                                

                                                                

 

                                                                

 

                                                                

 

C.                                                                

                                                                 

 

                                                                

 

                                                                

 

D. How does having light skin increase Darwinian fitness in humans living in cold climates closer to the north or south poles?

       It permits entry of radiation needed for vitamin           (especially vitamin D) synthesis.  At higher latitudes where it

is colder, there is less radiation and people spend more time   

indoors and covered up with warmer clothes.  Thus, they need

lighter skin to admit more radiation over shorter time periods. 

(4 pt.)

                                                                

 

8. (5) In 1979 and 1980, toxic shock syndrome was mostly found in women, rather than about equally in men and women, as it was after the mid-1980's.  The reason for this is

a. the appearance of a new strain of Staphylococcus aureus, which produces a toxin.

b. the introduction of highly absorbent tampons.

c. a change in the way the CDC records disease.

d. a misuse of penicillin antibiotics.

e. None of the above.

 

9. (16) A. What is the ultimate (evolutionary) cause of toxicity of plants?

 

Defense against herbivores.  (4 pt.)                                                                                               

                                                                                                                                                     

 

B. List two biological mechanisms that have evolved in humans and their ancestors to protect themselves from plant poisons.

 

i. There are many:  Visual recognition. / Taste associated with bad pervious experience. /               Vomiting. / Detoxification by the liver. / Excretion by the kidney. (4 pt.)

ii.                                                                                                                                                   

 

C. List one cultural mechanism humans have developed to protect themselves from plant poisons.

 

There are many: Eat before high poison concentration builds up. / Eat less poisonous parts. /       

Cook to inactivate toxins. / Breed less toxic varieties by artificial selection. (4 pt.)

D. Why is fruit typically not poisonous?   Unlike other plant parts, the normal function of fruit is   to be eaten so that by herbivores which disperse the seeds contained within the fruit.  (4 pt.)

                                                                                                                                                      

 

10. (18) A. Why does it usually increase both the mother’s and her embryo’s Darwinian fitness for pregnancy to lead to birth of a viable offspring?

                                                                         The mother achieves her fitness by producing       offspring.  The offspring can have no fitness of its own without being born.  (6 pt.)

                                                                                                                                                      

 

                                                                                                                                                     

 

B. If this is true, why do human mothers and embryos engage in conflicts in which the mother attempts to limit the embryo’s use of her resources?

                                                                                 Because the embryo can increase its fitness only by being born and obtaining as much resource as possible from the mother.  However, the

mother can improve her fitness both by giving the current embryo more or by saving the              

resources for her own maintenance or for investment in another offspring.  (6 pt.)

C. Describe one such conflict, naming hormones and other chemicals involved, if possible.

 

A mother will attempt to abort an embryo if its quality is in doubt by reducing lutenizing hormone.  The embryo secretes human chorionic gonadotropin to mimic LH and maintain pregnancy. / The     embryo secretes human placental lactogen to bind maternal insulin and increase her circulating glucose.  This would increase transfer of glucose to the embryo and increase its growth rate.  The mother responds by secreting more insulin to reduce her blood glucose concentraiton. / The mother and embryo engage in a similar contest over her blood pressure.  The   embryo tries to elevate it to increase blood flow to the placenta, and the mother tries to moderate blood pressure.

11. (21) A. What is gene flow? The movement of genes from one population to     

another. (7 pt.)

                                                                                                                                                      

 

B. What two things must an individual do to contribute to gene flow?

      i. It must move from one population to the other.                                                       

 

              ii.  It must reproduce after it gets there.    (7 pt.)                                                            

 

C. Briefly give two reasons why gene flow is important in evolution? 

i.                 It increases genetic variation within populations that receive gene flow.                

 

                                                                                                                                                      

 

ii. It tends to reduce differences in gene frequencies among populations.    (7 pt.)                 

 

                                                                                                                                                      

 

12. (16) A sequence of transformations for posture, vertebral function, and the forces imposed on the vertebral column occurs in the evolutionary line leading to humans.  What is the function of the vertebral column for transmission or resistance of force in each of the following groups.

 

A. Fish — The vertebral column has no role in resisting force and only transmits force force from   the tail to the head for swimming. (4 pt.)

                                                                                                                                                      

 

B. Quadrupedal Tetrapods (e.g., baboon, dog, lizard) — Some transmission of force from the        hind limbs to front of body, but mostly to resist the force of gravity pulling the body down and flexing the vertebral column downward (ventrally).  (4 pt.)                                                                

C. Bipedal Tetrapods (e.g., human) — Resistance to the force of gravity, which compresses the     vertebral column and flexes the vertebral into curves. (4 pt.)

                                                                                                                                                     

 

D. How have all or some of these transformations caused the common occurrence of lower back pain and injury in humans?

                                          In the human bipedal posture, the back must be curved to place the    

heavy head above the pelvis.  The weight of the upper body compresses the vertebral column,

accentuating its curvature, and causing chronic damage to the vertebral column.  This damage results in chronic pain and injury. (4 pt.)

 

 

13. (5 ea.) Define each of the following terms and state why they are important in evolution.  Do not define a term by example alone or using the term itself.

 

HEMOSTASIS - Termination of bleeding. Termination of bleeding is

crucial to maintain blood volume and pressure and to prevent

entry of pathogens into the body.                                

                                                                 

 

                                                                

 

EFFECTIVE POPULATION SIZE (Ne) — The number of individuals in the

breeding population.  This smaller this number is, the larger the

effect of genetic drift is.                                      

 

                                                                

 

                                                                

 

PHENOTYPIC PLASTICITY - Non-heritable changes in the value of the

phenotype in response to environmental factors experienced during

development.  This change can improve the performance of the       Individual or allow adjustment of the phenotype to unpredictable

short-term environmental changes.                                

 

                                                                

 

AUSTRALOPITHECUS - The genus of hominid from which our genus,   

Homo, apparently evolved.  It appeared about 4 Ma in the fossil

record and included 7 or 8 named species, 3 of which may have   

existed simultaneously.

                                                                

 

                                                                

 

CUCKOLDING - When a male is fooled by its mate into raising the 

offspring that she produced through fertilization by another    

male.  This can very adversely affect the male’s Darwinian      

fitness.

                                                                

 

                                                                 

 

END OF MIDTERM