BIOL 103 Test 1       2012

Name ______________________________________________

Total Points: 100

For calculations, SHOW ALL YOUR WORK or receive zero credit.

Cite SPECIFIC examples.

1. (10 pts) Explain an example of how muscle loss or “wasting” could be caused by an inherited genetic defect; and an alternative example of how muscle wasting could be caused by the environment.

Muscle loss could be caused by defect in a gene encoding an essential muscle protein. An example of such a defect is muscular dystrophy. Muscular dystrophy can show inheritance that is autosomal, or that is X-linked, if the muscle gene is on the X chromosome.

Muscle wasting can be caused by the environment, if an individual lacks sufficient food to maintain muscles. Alternative examples would be a disease such as AIDS or cancer that wastes muscle.

2. (20 pts) For a population of tortoises on a Galápagos island, assume exponential growth or death.

A. If there are 350 tortoises this year, and 380 tortoises four (4) years later, then what is the doubling time of the tortoise population?

N_t = N₀ • 2^(4 years / t years)

380 = 350 • 2^(4 years / t years)

Log10 (380/350) = Log10 [2^(4 years / t years)] = (4 years / t years) • Log10 (2)

t years = 4 years • Log10 (2) / Log10 (380/350) = 33.71 years

The doubling time of the tortoise population is 33.7 years.

B. Suppose instead that feral dogs prey on the tortoises, and their population declines from 350 to 300 in one year. After eight (8) years, how many will be left?

N_t = N₀ • Q^n

N_t = 350 tortoises • (300/350)^8  = 101.97 tortoises

After eight years in all, there will be about 102 tortoises.

Alternative answer:

N_t = 300 tortoises • (300/350)^8  = 87.41 tortoises

Eight years after the first-year decline, there will be about 87 tortoises.

3. (30 pts) A. Explain how this graph of two lemming populations shows an evolutionary strategy. How does natural selection cause lemmings to behave as they do?

This graph shows how two lemming populations repeatedly rise and crash. Lemmings increase exponentially; and the population that increases faster outcompetes the one that increases more slowly. If the two populations crash at the same rate, then the crash doesn’t “matter” in terms of overall success because with each exponential rise, the faster growing population gains even more of the proportion of reproductive success (number of offspring).

The same strategy works if one lemming population "out-crashes" the other population (survives more during a crash). For example, fewer members of one population might get caught by predators; or fewer might die crossing a river. The first population “wins” even though most individuals die at each crash.

It is important to note that at each crash, the lemming population risks total loss and extinction. But if extinction doesn’t occur, the survivors only “remember” their reproductive “success” in their genes. In fact all organisms have a history of exponential rise and crashes in their past; so the genes of all organisms favor exponential rise, when they get the chance (that is, sufficient habitat and resources).

B. How does Vonnegut suggest that humans follow an evolutionary strategy similar to lemmings? Cite one example from the book Galápagos.

In Galápagos, the humans overall are undergoing population boom and competition. The population crashes as individuals die in war and disease (exactly how is not clear, but it doesn’t matter for the story.)  A small population then ends up on a Galápagos island, where they immediately start breeding again (facilitated by Mary’s unusual form of assistance). The humans then start to breed exponentially, although their new habitat selects for different traits (streamlined head, lesser brains). Their numbers will eventually get checked by overgrowth and/or predation, like the lemmings.

Despite the crash, the new Galápagos humans “succeed” compared to the others because they “out-crashed” the rest of humanity.

4. (10 pts) Explain the inheritance of ONE of these conditions: Klinefelter syndrome, Turner syndrome, Trisomy X. 

Klinefelter’s syndrome occurs when a male inherits an extra X chromosome by mistake (XXY). The male has some physical abnormalities and may be infertile.

Turner’s syndrome occurs when a female inherits only one X chromosome from one parent. The individual has physical abnormalities and is usually infertile.

Trisomy X occurs when a female inherits an extra X chromosome from one parent (XXX). Trisomy X is surprisingly common, occurring in 1/1000 births. The effects may include increased height and learning difficulties; but in most cases the effects are so small, if any, that measuring them is controversial.

Explain how this kind of chromosome defect DIFFERS from the kind of defect causing hemophilia or Huntington’s disease.

All the above defects are abnormalities that involve a whole chromosome. Hemophilia and Huntington’s disease are caused by a defect in a single gene on a chromosome. Hemophilia involves an X-linked gene (recessive) whereas Huntington’s disease is inherited on an autosome (dominant).

5. (20 pts)  The Eloi are describes as having “rotundity,” that is, round childlike features. Suppose their allele frequency for rotundity is 0.85.

A. What proportion of the population is partly rotund, because each carries one rotund allele and one nonrotund allele?

The allele frequency p = 0.85

The trait frequency of full rotundity would be p^2 = (0.85)^2 = 0.7225

The trait frequency of partly rotund carriers are 2pq = 2 (0.85)(0.15) = 0.225

There are 22.5% partly rotund carriers.

B.  Suppose that the Eloi’s ancestors had a frequency of 0.02 for the rotundity allele. Explain what process led the allele frequency to change.

Several factors could lead the gene frequency to shift from 0.02 to 0.85.

If the population crashed to a small number, the effect of random variations would increase.  By chance, the few more rotund individuals might produce more offspring than the others. When the population rose again, the proportion of rotund individuals remained high.

Natural selection could also have driven the shift from 0.02 to 0.85. If the Eloi were very social, and preferred mating with social-appearing individuals, then they may have preferred to mate with more rotund, child-like individuals, and favored their offspring. Such a shift may be called “neoteny,” the tendency to favor child-like traits.

Most probably, both effects occurred (though full credit for an answer required describing only one).

6. (10 pts)  In The Time Machine, cite two different incidents in which the narrator lights a match.  Explain what the match symbolizes for the future of humanity.

There are many instances (only two were needed.)

The Time Traveler lights a match when he tries to find his stolen time machine.

He later lights a match while amusing the Eloi, and while trying to question Weena.

He lights a match to escape the Morlocks.

Upon returning to his own time, he lights a match to light his pipe.

Overall, the match symbolizes human knowledge and intellect--qualities forever lost in both the Eloi and the Morlocks. The book’s final sentence suggests that human kindness and caring may remain, but the intellect (in this story) is clearly lost.