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

In humans, curly hair (CC) is incompletely dominant to straight hair (SS).

A heterozygous human has wavy hair (CS).

Still other traits are incompletely dominant.

(This is most likely a polygenic trait)

Other traits are co-dominantThere are 4 blood types: A, B, AB, O Blood type is determined by 2 factors in the blood:

factors A and B. •If factor A is present, you are Type A.•If factor B is present, you are Type B.•If A and B factors are present, you are Type AB.•If neither factor is present, you are Type O.

• 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)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

• Thus eye color appears to vary on an almost continuous scale from brown to green to gray to blue

Eye Color

• 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

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)

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 activity

Eye Color

Hair color• Hair color is determined by 4

alleles on 2 genes:• Brown (HBr)• Blonde (HBd)• Red (hR)• Black (hbk)

• Thus hair color appears to vary on an almost continuous scale from black to brown to blond to red

• The brown and black pigment is melanin

• The red pigment is an iron- containing molecule

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

Skin Color

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