Evolution

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

A lactase-persistent person is lactose tolerant. A "lactase-persistent" adult continues to make the enzyme lactase and is able to digest (and tolerate) lactose.

Characteristics of natural selection:

- Every species contains individual genetic variation. - Individuals that are more successful have more surviving offspring, while individuals who are less successful have fewer surviving offspring. - Some individuals in the population will have more surviving offspring than others.

True or False. The pressures of natural selection lead to the development of perfectly fit organisms.

False.

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.

What is melanin's function?

Lighter skin has less of the dark-brown eumelanin that protects cells from UV damage.

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

The person is susceptible to malaria. The person is homozygous at the hemoglobin locus. A person with two copies of any allele is homozygous. A person with two normal copies of the hemoglobin allele is more susceptible to malaria than someone with a sickle cell hemoglobin allele.

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.

True or False. New genes can arise only through mutation of cells that give rise to eggs and sperm.

True.

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 Sheep can provide milk, which has about the same amount of lactose as cow's milk. Therefore, a lactase-persistence mutation could potentially be advantageous in this population.

Which of the following does NOT produce variation in populations? - bottleneck effect - independent assortment - mutation - crossing over

bottleneck effect

What primate is our closest living relative?

chimpanzee

In what way does natural selection depend on the specific environment in which an organism lives?

when the environment changes, traits that were beneficial to an organism may become harmful and vice versa. The evolution of a trait is often a balance of conflicting selective pressures that are influenced by the environment.

Four individuals measured their baseline blood glucose, then drank a litre of milk. They then measured their blood glucose levels at regular 15 minute intervals for 60 minutes. The results are shown in the graph below. Which individuals are lactase-persistent?

- Sarah - Peter Peter and Sarah's blood glucose levels both rose by more than 30 mg/dL, showing that their bodies digested lactose into glucose and galactose.

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

- Galactose - Glucose The lactase enzyme breaks the lactose disaccharide into two monosaccharides, glucose and galactose.

How could milk-drinking have provided strong favorable selection for lactase persistence?

- 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

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 mutations. Evidence of early milk use in lactase-persistent cultures provides evidence for the co-evolution of genes and culture.

Darker skin is more prevalent in high-UV areas. Dr. Nina Jablonski proposed a hypothesis to explain the selective pressure for darker skin in these environments. On what evidence did she base this hypothesis?

the melanin in darkly pigmented skin protects circulating folate from being destroyed by UV radiation, and folate is important in human reproduction This observation led Dr. Jablonski to propose that being able to protect folate from destruction by UV radiation would provide a selective advantage to individuals living in a high-UV environment.

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

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. Dr. Allison gathered blood samples from more than 5,000 children in East Africa. He analyzed the samples to identify malaria parasites and sickle cells. He found that children carrying the sickle cell character (or trait) had a lower parasite count, as if they were partially protected against malaria.

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. On the basis of this hypothesis, Dr. Allison predicted high frequencies of sickle cell disease only in areas where malaria is common.

Statements that apply to the variation in human skin color.

Human skin color variation is primarily determined by the type and amount of melanin pigment in the skin. Human skin color variation likely evolved in response to differences in the intensity of sunlight around the world. Human skin color variation evolved recently in hominid evolution, once some populations of our human ancestors migrated out of Africa. Evidence suggests that human skin color variation, which is determined by the amount and type of melanin in the skin, evolved in response to varying intensities of UV radiation in different parts of the world.

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

In areas with malaria, individuals with one sickle cell allele reproduced at higher rates than those with no sickle cell alleles. In areas without malaria, individuals with two sickle cell alleles reproduced at lower rates than those without sickle cell disease. 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.

Compare sickle cell disease and malaria.

Sickle cell disease and malaria are both potentially lethal diseases. Though malaria is an infectious disease and sickle cell disease is inherited, both can cause life-threatening conditions.

Which of the following is the best example of evolutionary fitness? - beetles that lay many eggs, with 90% of the offspring living to sexual maturity - a species of horse that mates with a species of donkey to produce the sterile mule - a pride of cats that forcibly takes over a more desirable habitat - mosquitoes that lay many eggs but the larvae are eaten by birds

beetles that lay many eggs, with 90% of the offspring living to sexual maturity

Based on the risk factors discussed in the video, which of the following groups would be most likely to develop the bone disease rickets?

children born to parents with dark skin living far from the equator Children born to parents with dark skin would likely have dark skin. Dark skin coupled with low UV intensity during winter months can limit vitamin D synthesis in the skin and lead to vitamin D deficiencies. In children, vitamin D deficiency can cause rickets.

Human populations in low-UV environments tend to have more lightly pigmented skin. One explanation is that the selective pressure for dark skin decreases as UV intensity decreases. At the same time, there is a selection for lighter skin to absorb more UV radiation, which is needed for vitamin D production. What evidence supports the vitamin D hypothesis for the evolution of lighter skin tones?

indigenous peoples living at high latitudes have darker skin, but they eat foods rich in vitamin D Populations that get ample vitamin D from their diets may therefore have had relaxed selection for lighter skin. This observation supports the idea that the need for vitamin D production provided the selective pressure for the evolution of lighter skin.