Physical characteristics and patterns of variation essay

Bring fact-checked results to the top of your browser search. In the United Statesfor example, the people identified as African Americans do not share a common set of physical characteristics. There is a greater range of skin colours, hair colours and textures, facial features, body sizes, and other physical traits in this category than in any other human aggregate identified as a single race. Features of African Americans vary from light skins, blue or gray eyes, and blond hair to dark skins, black eyes, and crinkly hair and include every range and combination of characteristics in between.

Physical characteristics and patterns of variation essay

Alternatively, photocopy a world map and have each group mark the distribution of each of the traits on their map. As a prelude to discussing the class's findings, ask your students to define "genotype" and "phenotype. What other factors might affect phenotype besides the genes? Note that with the exception of suntanning on skin color, the phenotypic traits above do closely reflect genotype.

Emphasize that very few traits are influenced by only one gene.

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Most traits are influenced by many genes, interacting with each other and with the environment in a very complex dance that scientists have barely begun to understand.

Discuss the class's findings. What surprised students the most? Does the geographic distribution of these traits match up and co-vary with what we conventionally think of as races? Or do the traits cut across racial lines?

For further discussion, have students explore the Human Diversity section select "Physical Appearance" of the RACE Web site to see how some of the traits we usually think of as racial are distributed geographically.

Between-Group Variation We've now seen how difficult it is to find a consistent racial classification system that works for everyone. Show the following two video clips. As they watch, ask students to look for three underlying characteristics of human variation that explain why racial classification doesn't work.

CLIP B 5 minutes - on skin color and gradual variation. Begins with Alan Goodman on the difficulty of measuring race, ends with Joseph Graves taking us on an imaginary walk from the tropics to the pole.

Begins with Alan Goodman talking about concordance, ends with the narrator explaining that sickle cell results from having ancestors who lived in malarial regions. Before moving on to a discussion of why racial classification doesn't work, make certain your students understand sickle cell trait and the skin color stories told in the film.

You can use the following handouts for this. For an excellent lab on how selective forces affect allele frequencies using the example of sickle cell, visit the Genetics Project Web site: Hemoglobin carries oxygen through the bloodstream to the body.

People who inherit two copies of the mutated hemoglobin gene, one from each parent, get sickle cell anemia. Their red blood cells become sticky and stiff and sometimes become sickle shaped. These "sickled" cells tend to get stuck in the narrow blood vessels known as capillaries, blocking the flow of blood.

Sickle cell anemia is a very painful disease and can be life threatening. But the larger number of people who inherit just a single copy of the mutated gene are known as sickle-cell carriers. They usually don't become anemic and interestingly, sickle cell carriers tend to be resistant to malaria, a deadly disease.

Malaria is caused by a parasite carried by the Anopheles mosquito.

Physical characteristics and patterns of variation essay

After humans started practicing agriculture, the mosquito thrived in standing pools of water that appeared on the cleared land.

Scientists believe that the sickle cell mutation arose independently four or five different times in human history, no more than 10, years ago, and probably much more recently.

Because carrying one sickle cell gene conferred a survival advantage in areas of the world where malaria was common, the sickle cell mutation was positively selected and passed on in those regions. As humans migrated, the sickle cell trait spread, not by contagion, of course, but through reproduction.

Population geneticists call it 'gene flow' when a gene variant like sickle cell passes from one population to another. As a result of these historical and environmental influences, sickle cell is commonly found in central and western Africa, but not Southern Africa. It is also found on the Arabian peninsula and over into India, as well as up through Turkey, Greece, Albania, Sicily and Italy and other parts of the Mediterranean basin.

Carrying the sickle cell variant of the hemoglobin gene, therefore, is a marker not of race, but of descent from people who once lived where malaria was common. For a map showing the spread of sickle cell, click here and scroll down to the map images.

This disease is known as thalassemia. Skin Color Handout Why do we have different skin colors?

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Scientists can only hypothesize at this point because the genetics of skin color is poorly understood. But we do know that skin color tends to correlate not with 'race' but with the amount of ultraviolet radiation in the environment.

People in equatorial areas of the world, where sunlight is most intense, have the darkest skin.However, cross-national comparisons of workplace safety, other occupational health characteristics, labor market patterns, and work-related policies were beyond the scope of the panel’s review.

QUESTION 2. AP Biology Essay Questions 1. The unique properties (characteristics) of water make life possible on Earth. Select three properties of water and: a for each property, identify and define the property and explain it in terms of the Genetic variation is the raw material for evolution.

Physical Characteristics and Patterns of Variation Introduction Many generalizations are made about things and people, their physical characteristics, specific traits that sets one apart from the other.

Human physical variation is continuous and available evidence suggests that gene flow among human populations throughout their history has been the rule rather than the exception. Humans are characterized by their bipedalism and their lack of significant body hair. Physical Characteristics and Patterns of Variation Essay - Physical Characteristics and Patterns of Variation Introduction Many generalizations are made about things and people, their physical characteristics, specific traits that sets one apart from the other.

Physical Characteristics and Patterns of Variation Introduction Many generalizations are made about things and people, their physical characteristics, specific traits that sets one apart from the other.

Physical Characteristics and Patterns of Variation Essay - Physical Characteristics and Patterns of Variation Introduction Many generalizations are made about things and people, their physical characteristics, specific traits that sets one apart from the other. “Race” and the reality of human physical variation. Scientists have known for many decades that there is little correlation between “race,” used in its popular sense, and actual physical variations in the human arteensevilla.com the United States, for example, the people identified as African Americans do not share a common set of physical characteristics. Physical Characteristics and Patterns of Variation Introduction Many generalizations are made about things and people, their physical characteristics, specific traits that sets one apart from the other.
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