Human Genetics

We are all a combination of genes and traits from our parents.

Some human traits are dominant and recessive, just like Mendel’s pea plants No Cleft is dominant, cleft chin is recessive Free (unattached) earlobe is dominant, attached is recessive

curly hair (CC) In humans, curly hair (CC) straight hair (SS). is incompletely dominant to straight hair (SS). wavy hair (CS). A heterozygous human has wavy hair (CS). Still other traits are incompletely dominant. (This is most likely a polygenic trait)

Other traits are co-dominant ABABO  There are 4 blood types: A, B, AB, O A B  Blood type is determined by 2 factors in the blood: factors A and B. factor AType A If factor A is present, you are Type A. factor BType B If factor B is present, you are Type B. ABType AB If A and B factors are present, you are Type AB. neither factorType O. If neither factor is present, you are Type O. both The A and B factors are co-dominant; when both are present, both are expressed. Type O is recessive (needs two O genes to be present). BLOOD TYPE: an example of co-dominance in humans

Many traits are polygenic (determined by more than one gene) determined by more than one genepolygenic When a trait is determined by more than one gene, we say that it is polygenic. blood type eye color Height is a polygenic trait Also: hair color Polygenic Inheritance

Eye color is determined by 3 genes brown greengray blueThus eye color appears to vary on an almost continuous scale from brown to green to gray to blue Eye Color melanin blue green Eye color is determined by three genes: one controls texture of the iris which refracts light to make blue, and a second which determines the amount of pigment, called melanin. When a small amount of melanin is present, blue or green eyes result, while brown & black eyes result from increasing amounts of melanin

brown, green blackredviolet polygenic). Eye colors can range from the most common color, brown, to the least common, green. Rare genetic specialties can even lead to unusual eye colors: black, red, and violet. Eye color is an inherited trait influenced by more than one gene (polygenic). Heterochromia (eyes that are different colors) Brown (B)blue (b)Brown blue Green / hazel(G)lighter color(g). Green lighter-color There are 3 genes that control eye color. One gene has Brown (B) and blue (b) alleles (Brown is dominant over blue). The 2nd gene also has 2 alleles: Green / hazel (G) and lighter color (g). Green is dominant over the lighter-color allele. Eye Color Calculator activityCalculator Eye Color

Hair color Hair color is determined by 4 alleles on 2 genes:Hair color is determined by 4 alleles on 2 genes: Brown (H Br )Brown (H Br ) Blonde (H Bd )Blonde (H Bd ) Red (h R )Red (h R ) Black (h bk )Black (h bk ) Thus hair color appears to vary on an almost continuous scale from black to brown to blond to redThus hair color appears to vary on an almost continuous scale from black to brown to blond to red The brown and black pigment is melaninThe brown and black pigment is melanin The red pigment is an iron- containing moleculeThe red pigment is an iron- containing molecule

melanin, Skin color is determined by the amount and type of melanin, the pigment in the skin. Skin color is determined by 3 genes (6 different alleles), which accounts for the vast range of different skin colors in human beings. link Skin Color

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