ANATOMYHave Biology of Skin Color out with your answers

BIOLOGY OF SKIN COLOR

(Sub-Saharan African, Indian, Southern European, and Northern European)

There are no people who actually have true black, white, red, or yellow skin. 

These are commonly used color terms that do not reflect biological reality.

Very little of the skin is actually involved in skin-color difference.

PIGMENTATION OF SKINa. Pigment (melanin) produced by

melanocytesi. Color is yellow to brown to black

b. Melanocytes are mostly in the stratum basale

i. Amount of melanin produced depends upon genetics and exposure to sunlight

Everyone has melanin. The ONLY difference is the amount

of melanin.

OTHER PIGMENTATION DETERMINANTS

i. Carotene1. Orange-yellow pigment from some

vegetablesii. Hemoglobin

1. Red coloring from blood cells in dermis capillaries

2. Oxygen content determines the extent of red coloring

SKIN COLOR AND RACEThere are NO reliable genetic

markers for race. (ie. There is no gene for race)

The concept of race is made-up.The “false” concept of race can

be traced to the history of European colonization- people really like to categorize.

As a species, all humans originated in Africa.

WHY HAVE DIFFERENT SHADES?Remember: we all share melanin

production in the melanocytes at the lowest level of the epidermis.Balance between protection against

UV decomposition & use of UV to synthesize Vitamin D.

The skin uses UV light to synthesize vitamin D, ~1 hour a week is all that is needed.

BUT, UV breaks down folic acid (Vitamin B) in the body. A lack of folic acid can lead to birth

defects & deformed sperm

GEOGRAPHY = SUNLIGHT INTENSITY!Near the equator the amount of

sunlight is much more than what is needed to synthesize vit D.Too much exposure increases the

risk of birth defects (lack of folic acid), defective sperm & skin cancer.

Thus, an increase in melanin (which absorbs UV and protects the folic acid & DNA) was selected for since humans with more melanin more likely to survive.

EVOLUTION OF SKIN COLOREvolution of humans near the equator

in Africa benefited from an increase in the production of melanin.

BUT As people migrated, particularly far north of the equator (less intensity and length of light) the need for UV (vitamin D) outweighed the protection from destruction of folic acid & UV (birth defects & cancer).

(Data for native populations collected by R. Biasutti prior to 1940.)

Review your answers for # 1-5 of “Biology of Skin Color”. You should all have the same answers in general.

Then #6 & 6a- please discuss your answers as this is a more difficult question. As a group discuss 6a and try to come up with the best way to depict the relationship between UV, skin color and folic acid/folate/vit B

ON POSTER PAPER: create your final diagram of 6a. We will be hanging them in the room

4. We will discuss 7-9 next class. HW: Read Survival of the sickest and answer the

questions.

Have Survival of the sickest out AND bio of skin color.

1st period- make a final diagram of your #6 based on your groups understanding.

1st & 4th period- discussion about the articles Lecture on cancer & burns Begin disease reports HW: research disease reports and WP #4

cancer and burns

DIAGRAMMING COMPLEX IDEAS

A picture is worth a thousand words. The idea behind this question is to turn a

complicated hypothesis into an easier to understand picture.

Your challenge is to take your diagram as it is now

Sun breaks down foliate.High UV able to synth vit D

Melanin protects foliate.High UV able to synth vit D

Low UV still able to synth vit D for Ca absorption.No affect on foliate.

Melanin blocks too much UV and skin cannot make vit D thus brittle bones. Low UV doesn’t affect foliate.

Sun breaks down foliate.High UV able to synth vit D

Melanin protects foliate.High UV able to synth vit D

Low UV still able to synth vit D for Ca absorption.No affect on foliate.

Melanin blocks too much UV and skin cannot make vit D thus brittle bones. Low UV doesn’t affect foliate.