1. Human Genetics
Biology Honors

2. Human Chromosomes
Autosomes – 44 chromosomes that everyone has no matter what sex they are
Sex chromosomes – 2 chromosomes that determine sex
Females = XX, Males = XY

3. How is sex determined? Eggs = 22 autosomes, 1 sex chromosome (X)
Sperm = 22 autosomes, 1 sex chromosome (X or Y)

4. Simple Dominant/Recessive Traits
Many human genes are inherited as dominant or recessive traits just like the traits Mendel studied in peas
Ear lobes provide an example of this:
Unattached ear lobes are inherited as a dominant trait.
Attached ear lobes are inherited as a recessive trait.

5. Simple Dominant/Recessive Traits
Having a bent little finger is a dominant trait

6. Dominant/Recessive Human Traits
Albinism
Absence of pigment from the skin, eyes and hair
Albinism is a recessive trait.
Brown teeth
Teeth have a brown color that is not the result of poor oral hygiene or antibiotics taken as a child
White teeth are dominant.

7. Dominant/Recessive Human Traits
Cleft chin
A noticeable indentation at the center of the chin
Having a cleft chin is dominant to a smooth chin
Double-jointed thumbs
This is commonly called a hitchhiker's thumb
The thumb can bend back at almost 90 degrees.
Hitchhiker's thumb is a recessive trait

8. Dominant/Recessive Human Traits
Hand folding
When the hands are folded either the left or right thumb will be on top
Left thumb on top is dominant.
Mid-digital hair
Hair growing from the middle section of each finger
Hair presence is dominant
PTC tasting
Phenylthiocarbamide (PTC) is a chemical that cannot be tasted by some individuals.
Tasting is dominant to the inability to taste PTC.

9. Dominant/Recessive Human Traits
Tongue rolling
Ability to form a tube with your tongue
Rolling is dominant
Widow's peak
A sharp point in the hairline that points toward the nose
Having a widow's peak is dominant to a smooth hairline

10. Specific Human Traits Dimples Freckles Hair whorling
Round indentations in the cheeks when smiling, not lines or clefts
Freckles
Small patches of darker pigmented skin on various parts of the body
These may be present on both dark and light skinned individuals.
Hair whorling
These may be referred to as cowlicks.
Areas in which hair grows from your scalp in a whorl instead of in a given direction.

11. Specific Human Traits Myopia Polydactyly
Short sightedness, the inability to see far off objects without correction by glasses or contacts
Polydactyly
Having more than five digits on each hand and foot.

12. Specific Human Traits S-methyl thioester smeller White forelock
S-methyl thioesters are produced in the urine after consumption of asparagus. Some individuals cannot smell this substance. If you smell a strong odor on urination after eating at least 5 asparagus spears, you are an S-methyl thioester smeller.
White forelock
A white patch of hair at the front of the scalp.

13. Multiple Alleles Determined by more than one gene Example: eye color
Eye color is determined by two genes
one controls texture of the iris which refracts light to make blue.
A second determines relative abundance of melanin.
When a small amount of melanin is present, green eyes result while brown and black eyes result from relatively increasing amounts of melanin

14. Multiple Alleles Hair color is determined by more than one gene
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