Human Genetics

What Genes do you have?

What is a trait?

• “Your Mom gives you ½ of the instructions, your Dad gives you the other ½.”

• In science jargon: Your Mom gives you one allele of that gene and your Dad gives you one allele of that gene and you put them together to make a chromosome.

Genotype vs Phenotype

• What instructions or genes you have from your parents are said to be your genotype

• What people see on the outside is your phenotype

• So your genotype determines your phenotype!

Dominant Traits

• When alleles get together, some alleles are “stronger” than other alleles.

• We call these alleles dominant and then the trait that they express the dominant trait.

• Both parents might give you instructions on how your ear lobes will look, but some looks are dominant (stronger) than others

• Let’s try a simulation…

Male or Female?

• Your sex is determined by whether

• you get an X or Y chromosome from your father.

• Everyone receives an X from their mother.

• Women = XX• Men = XY

Ear Lobes

• Free earlobes (dominant trait) hang below the point of attachment to the head. 

• Attached ear lobes (recessive trait) are attached directly to the side of the head.

Traits inherited

The physical characteristics below are common genetic traits inherited from one generation to the next:

Free vs. Attached Earlobes Straight vs. Curved Thumbs Bent vs. Straight Pinky With vs. Without White Forelock

Thumbs

• Straight thumbs (dominant trait) can be seen as nearly a straight line and may contain a slight arch when viewed from the side as in the illustrations. 

• Curved thumbs (recessive trait) can be seen as part of a circle.

Pinky?

Bent pinky (dominant trait) vs. Straight pinky (recessive trait):

1. Hold your hands together as if you are covering your face.

2. If the tips of the pinkies (or baby fingers) point away from one another, the pinkies are bent (recessive trait).

Forelock

• A White Forelock (dominant trait) is a patch of white hair, usually located at the hairline just above the forehead. The photo to the left clearly shows an exaggerated white forelock.

• No White Forelock is the recessive trait.

Cleft Chin

• No cleft dominant, • cleft recessive

Widows Peak

• Widow peak dominant• straight hairline

recessive

Freckles

•  Freckles dominant, no freckles recessive

Tongue Roller vs Non Roller

•  Roller dominant, nonroller recessive

• Folding Inability dominant, ability recessive

Dimples vs No Dimples

• Dimples are thought to be Dominant• No dimples is recessive.

Hand Clasping

• Hand clasping is believed to be determined by genetic factors,

• although it is unclear if one trait is dominant over the other.

• 55%= Left• 45% right

Bent Finger

• Having a bent little finger is a dominant trait

Multiple Alleles• Eye color is determined by more than one gene

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

Eye color is determined by two Eye color is determined by two genes, genes, one controls texture of the iris one controls texture of the iris

which refracts light to make which refracts light to make blue. blue. A second determines A second determines

relative abundance of relative abundance of melanin. melanin.

When a small amount of When a small amount of melanin is present, green melanin is present, green eyes result while brown and eyes result while brown and black eyes result from black eyes result from relatively increasing relatively increasing amounts of melaninamounts of melanin