Genetic Traits, Lecture notes of Genetics

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Genetic Traits

Mendelian traits in humans

• In Mendelian inheritance, a child receiving a dominant allele from either parent will have the dominant form of the phenotypic trait or characteristic. Only those that received the recessive allele from both parents, known as zygosity, will have the recessive phenotype. Those that receive a dominant allele from one parent and a recessive allele from the other parent will have the dominant form of the trait.

Earlobe

Attachment

Attached ear lobes are attached directly to the side of the head

Some scientists have reported

that this trait is due to a single

gene for which unattached

earlobes is dominant and an

attached earlobe is recessive.

Other scientists have reported

that this trait is probably due

to several genes.

Broad Nose

Narrow Nose

Broad Nose - nostrils

extend beyond the space

between the eyes

Narrow Nose - nostril span

restricted to the space

between the eyes

Thumb

Extension

Bent Little Finger

A dominant allele causes the last

joint of the little finger to

dramatically bend inward toward

the 4th finger. Lay both hands flat

on a table relax your muscles, and

note whether you have a bent or

straight little finger.

Mid-digital Hair

Some people have hair on the middle

segment of one or more of their fingers,

while others don't. Having any hair there

at all means that you have the dominant

phenotype. Complete absence of hair is

recessive.

Longer 2nd toe is dominant over

2nd toe shorter than big toe.

Tongue

Rolling

70% of people of European ancestry could roll their tongues and the remaining 30% could not.

Dimples

Dimples are reportedly due to

a single gene with dimples

dominant (people may exibit a

dimple on only one side of the

face) and a lack of dimples is

recessive.

Cleft chin is dominant over no

cleft

Handednes

s

Overall, about 10% of people are left-handed, but the number varies among cultures from 0.5% to 24%. Some scientists have reported that handedness is due to a single gene with right handedness dominant and left handedness recessive. Multiple studies present evidence that handedness is controlled by many genes—at least 30 and as many as 100—each with a small effect; many are linked to brain development. Environment also plays an important role: some cultures actively discourage left-handedness.