Human Genetics Biology Honors

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

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

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.

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

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.

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

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.

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

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.

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.

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.

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

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