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Exam 16: How Populations Evolve

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Question 31

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What type of selection is occurring in a population if the distribution graph shifts from the left end of the spectrum to the far right end?

A) directional
B) stabilizing
C) disruptive
D) Populations do not undergo selection, they are fixed.

E) B) and D)
F) None of the above

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Question 32

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Hospital data shows that human infants born with an intermediate birth weight have a better chance of survival than those that weigh much less or much more than usual. Larger than normal babies may have a difficult delivery, while smaller than normal babies may not be fully developed. What type of selection is occurring? Is the variability in birth weight in human populations increasing or decreasing? Explain what the normal population distribution would look like on a scale of 1 - 20. Explain what the distribution would look like after many generations and indicate the phenotype selected.

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This is stabilizing selection. As genera...

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Question 33

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Explain why male baboons have evolved to be larger than the females of the species?

While we have seen how natural selection and the use of pesticides can lead to the development of resistant varieties of insects, two economically important flies, the Mediterranean fruit fly (Medfly) and the screwworm fly, can be driven to local extinction by the continuous release of sterile flies of those species. The critical factor is that the female of these species only mates once. But which of the following is/are also necessary for sterile release to work?

What is the term used to describe the changes in allele frequencies of a population over generations?

Over the course of millions of years various environments have changed. As grasslands slowly took the place of forests the inhabitants were forced to adapt or they went extinct. During this time period the horse evolved from a small cat sized creature to the size of the modern horses we see today. This is an example of which type of natural selection?

Our domesticated honey bee-originally from Europe-is slow to sting, requires abundant flower nectar, gets up late in the morning, and stores much honey but only produces enough new brood to swarm once a year. Because the European honey bee was performing poorly as a honey producer in South America, the African subspecies was imported in a breeding experiment. The African honey bee formed small nests, foraged earlier and on smaller nectar sources, produced less honey stores and more brood, swarmed four or five times a year, and was fast to sting. However, when the African queens escaped, the two populations interbred and the African genotype spread several hundred miles north each year. Surprisingly, a hundred miles behind the expanding range of the African honey bees, the European and hybrid strains died out and the bees were essentially 100 percent African. How would this be explained in evolutionary genetics terms?

Amish populations in Lancaster County, Pennsylvania have high rates of a rare form of dwarfism. The recessive allele that codes for this disorder is found in 1 of 14 individuals in this Amish population, in contrast to 1 in 1,000 in the general population. In Ohio, an Amish population suffers with higher than normal rates of cystic fibrosis and a host of other genetic diseases so rare that some have not yet been named. What factors have caused such severe genetic problems in these two communities?

In a population, the allele frequency for red flower color remained at 0.7 and the allele frequency for white flower remained at 0.3 for six generations. This ____ an example of a Hardy-Weinberg equilibrium in that ___________.

The most common source of genetic variation in sexually reproducing organisms is

Scientists have studied, in detail, the evolution of the peppered moth, Biston betularia, over the last two hundred years. The peppered moths rest on tree trunks and are a tempting treat for birds in the area. In the mid -1800's the trees in their England habitat were covered with lichens, which are a light, grayish - green color. Although color variations occurred, the vast majority of the moths were light-colored. Because their light coloration effectively camouflaged them against the lichens-covered trees, they were not as easily seen by birds as darker colored moths. The light colored moths flourished. The environment changed, as the Industrial Revolution progressed. By 1900, the lichens had died and trees were coated with soot due to the industrial pollution. The lighter colored moths were no longer 'hidden' in their environment, and in fact, were easily seen by their predators. Their numbers dwindled. At the same time, the darker-colored moths flourished because of their ability to hide on the darkened trees. As environmental standards have been implemented, environmental conditions have shifted, allowing lichens to grow on tree trunks. Describe what the initial normal population curve would look like before pollution. Describe what the population curve would look like after the Industrial Revolution and indicated what phenotype was favored.

Which of the following conditions is not necessary to maintain the Hardy-Weinberg equilibrium?

The bottleneck effect is thought to be responsible for the loss of genetic variability in a species.

Natural selection can maintain genetic variation by favoring heterozygous genotypes. In equatorial Africa, the best genotype to have for hemoglobin is heterozygous (HbA / HbS). In the United States of America, there is no advantage to the heterozygous genotype. HbA codes for normal hemoglobin, whereas HbS codes for an abnormal hemoglobin that causes red blood cells to become distorted in shape (sickle cell). Explain why the heterozygous state is advantageous in Africa, but not in the USA. What has happened to the sickle cell allele in Africa? What has happened to the sickle cell allele in the United States?

A random alteration in the sequence of DNA nucleotides that provides a new variant allele is

Which genotype is most likely to survive in a region of the world that contains malaria?