Chapter 19 Questions

Place the following ancestors in order of earliest (1) to most recent (5).

(1) last common ancestor of chimpanzees and humans; (2) Ardipithecus ramidus;(3) Australopithecus; (4) Homo erectus; (5) Homo sapiens

What percentage of DNA sequences do all humans share?

>99%

What can you infer about the skin-color alleles of a light-skinned person and of a dark-skinned person?

A dark-skinned person would have more alleles to produce melanin.

A person has dark skin. Based on that knowledge, can you predict what blood type this individual is likely to have? Conversely, if you know that a person has type A blood, can you predict what skin color this individual is likely to have?

A person with dark skin could have any blood type. A person with type A blood could have any skin color. There is a huge amount of variation in a trait like blood type, even in a population of people of similar skin color.

According to the out-of-Africa hypothesis of human origins and migration, which group of people should show the highest level of genetic diversity?

Africans

This map shows predicted skin pigment based on UVB intensity. What would you expect to see if UVB intensity increased in an area?

Average skin pigmentation would increase.

The ancestors of modern humans evolved in a high-UV environment. What does this suggest about their skin color?

Darker skin confers protection from UV destruction of folate, while still permitting vitamin D synthesis in a high-UV environment. Their skin color was likely dark.

Why dark skin in High UV- light?

Darker skin protects folate while allowing vitamin D production

What sources of evidence are used to determine where humans evolved?

Dating fossil remains, Genetic variation, and Relatedness among people from different areas

Skin color is affected by

Exposure to sunlight, the amount and type of melanin produced by melanocytes, and the UV light intensity of the area a person's ancestors lived in

Variations in skin tone correlate with a balance between these two vitamins

Folate and Vitamin D

Jablonski and Chaplin hypothesized that darker skin is advantageous in _______ UV environments because darker skin _______ .

High-; protects folate from degradation

Which statement is a correct description of the relationship between UV light in the environment and how it affects humans?

In a high-UV-light environment, more melanin is likely to be produced.

How is nuclear DNA transmitted?

Inherited by all children from both their mother and their father

How is mtDNA transmitted?

Inherited by all children only from their mother

How is Y-chromosome transmitted?

Inherited only by sons from their father

In the course of human evolution, which of the following environmental factors likely influenced whether a population had mostly light-skinned individuals or mostly dark-skinned individuals?

Levels of UV light

Why light skin in Low UV- light?

Lighter skin allows for vitamin D production without folate destruction

Light skin would be an evolutionary advantage in which area?

Low-UV-light environments

Why is only maternal mitochondrial DNA useful for studying human evolution?

Maternal mtDNA is the only type that is passed to offspring.

Who is Mitochondrial Eve, and when did she live?

MtEve is a single female ancestor of all modern humans. mtEve lived in eastern Africa between 200,000 and 150,000 years ago.

Why is having light or dark skin an evolutionary advantage in certain environments?

Skin color could protect folate levels in some environments or promote vitamin D production in others.

Scientists have studied patterns of mitochondrial DNA to determine where humans first evolved and how they spread. Humans inherit their mitochondrial genes only from their mothers. Why aren't a father's mitochondrial genes passed to his offspring?

Sperm do not contribute their mitochondria to the zygote.

A person's skin tone is influenced by ________.

The amount of melanin present in the skin, the person's genetic ancestry and the types of alleles he or she carries, the amount of sunlight to which a person is exposed, which temporarily causes the skin to increase melanin production.

Our closest primate relatives, chimpanzees, have light-colored skin yet live in tropical (high-UV) environments. How would the Jablonski-Chaplin hypothesis explain this observation?

The hair of chimpanzees protects their light skin from UV light.

Why is there so much variation in human skin coloration?

Variation occurs because humans are found in areas that range from high-UV-light environments to low-UV-light environments, Variation occurs because alleles that are harmful in one environmental context may be beneficial in another, Variation occurs because humans underwent natural selection, which resulted in traits that conferred advantages to humans becoming fixed in populations, and variation occurs because skin coloration results in different advantages, depending on the levels of sun in the region.

Which of the following would help darker-skinned people who live in low-UV environments remain healthy?

Vitamin D supplementation

The darker the skin of a person, the more likely that some of that person's ancestors _______.

Were from a geographical area closer to the equator

In modern humans, African populations are _______ and have _____genetic diversity than non-African populations.

older,more