Microevolution Tutorials

What is a gene pool?

a hypothetical collection of all the possible alleles in a population

Suppose that a mutation for lactase-persistence occurred in each of the populations described below. In which populations would the mutation be more likely to increase in frequency over time because of natural selection?

a population that raises wheat and sheep

How does the term "lactase persistent" relate to the term "lactose tolerant"?

A lactase-persistent person is lactose tolerant.

Which discovery supports the hypothesis that evolution of the lactase-persistence trait was driven by the use of milk in pastoralist cultures?

Ancient pots used to hold milk are about the same age as the lactase-persistence mutation (Evidence of early milk use in lactase-persistent cultures provides evidence for the co-evolution of genes and culture.)

Populations evolve for many reasons. Suppose there is a population of plants that have either purple flowers or white flowers, and the allele for purple flowers is dominant. This means that plants with two purple alleles have purple flowers. Plants with one purple allele and one white allele also have purple flowers. Only plants with two white alleles have white flowers. For each event or condition described below, answer the following questions. Which mechanism of evolution is at work? How does this event affect the population's gene pool? Do the frequencies of the two alleles change, and if so, how?

Event or Condition 1. During an extreme heat wave, plants with white flowers survive better. 2. A person uproots the five closest plants, which all happen to have white flowers 3. A storm kills many plants at random 4. Plants with purple flowers attract more insects, which pollinate plants. 5. Workers from a nearby greenhouse accidentally introduce white flower seeds into this population's habitat. Mechanism 1a. Natural Selection 2c. Genetic Drift 3e. Genetic Drift 4g. Natural Selection 5i. Gene flow Effect on Allele frequencies 1b. Frequency of white allele increases 2d. Frequency of purple allele increases 3f. Allele frequencies change but not predictably 4h. Frequency of purple allele increases 5j. Frequency of white allele increases

How did Dr. Allison test his hypothesis that sickle cell disease was connected to malaria? (2 things)

He expanded his study area beyond Kenya to the rest of East Africa to see if malaria and sickle disease were connected. He evaluated blood samples for malaria parasites and the presence of sickle cells.

In 1949, Dr. Tony Allison observed a high frequency of Kenyans carrying the sickle cell allele in coastal areas and near Lake Victoria, but a lower frequency in the highlands. What did he hypothesize?

He hypothesized that there was a connection between malaria and sickle cell disease.

A hypothetical population of 200 cats has two alleles, TL and TS, for a locus that codes for tail length. The table below describes the phenotypes of cats with each possible genotype, as well as the number of individuals in the population with each genotype. What statements about the population are true? (5 things)

Heterozygotes make up 20% of the population Homozygotes make up 80% of the population In the entire cat population, 60% of the alleles are T^s In the entire cat population, the frequency of the T^l allele is .4 Assuming random mating, each gamete has 40% chance of having a T^l allele and a 60% chance of having a T^s allele

What did researchers discover about the genetic mutation causing lactase persistence?

It is found in a regulatory region (a "switch") upstream of the lactase gene (All known mutations giving rise to lactase persistence are in a genetic "switch" that regulates expression of the lactase gene. Mutations in regulatory regions can change the amount of protein that is produced without affecting its structure or function.)

How does Dr. Allison's work provide an example of natural selection in humans? (2 things)

In areas without malaria, individuals with two sickle cell alleles reproduced at lower rates than those without sickle cell disease. In areas with malaria, individuals with one sickle cell allele reproduced at higher rates than those with no sickle cell alleles. (In different environments, natural selection favors different characteristics. In areas with malaria, the reproductive advantages of having one sickle cell allele (and some protection from malaria) kept the allele at high frequencies in the population. In areas without malaria, the reproductive disadvantages from sickle cell disease reduced the allele in populations.)

In some populations, 1 in 500 people have sickle cell disease. What reason does the film give for why a potentially deadly, inherited disease is found at such high frequencies?

Individuals with one sickle cell allele are protected from malaria and do not have sickle cell disease, thus keeping the allele in the population. (People with one sickle cell allele are protected from malaria, but do not have sickle cell disease. Protection from malaria comes at the cost of more sickle cell disease in the population.)

How could milk-drinking have provided strong favorable selection for lactase persistence? (3 things)

Milk may have been a critical food source during times of famine. Milk is protein and fat-rich and therefore could have been an important, high-quality food source. Milk was safer to drink than water and reduced exposure to pathogens

The three major mechanisms of evolution differ in how they work, and as a result often have different effects on a population. Review your understanding of natural selection, genetic drift, and gene flow by sorting the statements below into the correct bins. Drag each statement into the appropriate bin depending on whether it applies to natural selection, genetic drift, or gene flow.

Natural Selection Consistently causes a population to become better adapted to its environment A result of differential success in reproduction Cannot cause a harmful allele to become more common Genetic Drift Responsible for the founder effect Responsible for the bottleneck effect Causes allele frequencies to fluctuate randomly Gene flow Can introduce new alleles into a population's gene pool A result of the movement of fertile individuals or their gametes

Compare sickle cell disease and malaria.

Sickle cell disease and malaria are both potentially lethal diseases.

Suppose that Gene BB occurs in a sea turtle gene pool where the frequency of the B1B1 allele is 0.5 and the frequency of the B2B2 allele is 0.4. What is the frequency of the B3B3 allele, assuming that there are only three alleles in the population?

The frequency of B3=0.1B3=0.1 because 0.5+0.4+?=10.5+0.4+?=1.

If a person has two normal copies of the hemoglobin allele, which statements are true? (2)

The person is homozygous at the hemoglobin locus. The person is susceptible to malaria.

Predict what will happen to the frequency of the sickle cell allele in areas where malaria has been eradicated.

The sickle cell allele will decrease in frequency. (Without malaria, selection for the sickle cell allele decreases. As a result, the frequency will likely decrease.)

The enzyme lactase breaks the sugar lactose into which compound(s)?

glucose and galactose