Human GeneticsHuman Genetics

Biology HonorsBiology Honors

Human ChromosomesHuman Chromosomes

Autosomes – 44 Autosomes – 44 chromosomes that chromosomes that everyone has no everyone has no matter what sex they matter what sex they areare

Sex chromosomes – 2 Sex chromosomes – 2 chromosomes that chromosomes that determine sexdetermine sex

Females = XX, Males = Females = XX, Males = XYXY

How is sex determined?How is sex determined?

Eggs = 22 autosomes, 1 sex chromosome (X)Eggs = 22 autosomes, 1 sex chromosome (X) Sperm = 22 autosomes, 1 sex chromosome Sperm = 22 autosomes, 1 sex chromosome

(X or Y)(X or Y)

Simple Dominant/Recessive Simple Dominant/Recessive TraitsTraits

Many human genes are inherited as Many human genes are inherited as dominant or recessive traits just like dominant or recessive traits just like the traits Mendel studied in peasthe traits Mendel studied in peas

Ear lobes provide an example of this:Ear lobes provide an example of this:

Attached ear lobes are inherited as a recessive trait.

Unattached ear lobes are inherited as a dominant trait.

Simple Dominant/Recessive Simple Dominant/Recessive TraitsTraits

Having a bent little finger is a Having a bent little finger is a dominant traitdominant trait

Dominant/Recessive Human Dominant/Recessive Human TraitsTraits

AlbinismAlbinism – Absence of pigment from Absence of pigment from

the skin, eyes and hairthe skin, eyes and hair– Albinism is a recessive Albinism is a recessive

trait.trait. Brown teeth Brown teeth

– Teeth have a brown color Teeth have a brown color that is not the result of that is not the result of poor oral hygiene or poor oral hygiene or antibiotics taken as a childantibiotics taken as a child

– White teeth are dominant.White teeth are dominant.

Dominant/Recessive Human Dominant/Recessive Human TraitsTraits

Cleft chin Cleft chin – A noticeable indentation A noticeable indentation

at the center of the chinat the center of the chin– Having a cleft chin is Having a cleft chin is

dominant to a smooth dominant to a smooth chinchin

Double-jointed Double-jointed thumbs thumbs – This is commonly called a This is commonly called a

hitchhiker's thumb hitchhiker's thumb – The thumb can bend back The thumb can bend back

at almost 90 degrees.at almost 90 degrees.– Hitchhiker's thumb is a Hitchhiker's thumb is a

recessive traitrecessive trait

Dominant/Recessive Human Dominant/Recessive Human TraitsTraits

Hand folding Hand folding – When the hands are folded either the left or When the hands are folded either the left or

right thumb will be on top right thumb will be on top – Left thumb on top is dominant.Left thumb on top is dominant.

Mid-digital hair Mid-digital hair – Hair growing from the middle section of each Hair growing from the middle section of each

fingerfinger– Hair presence is dominantHair presence is dominant

PTC tasting PTC tasting – Phenylthiocarbamide (PTC) is a chemical that Phenylthiocarbamide (PTC) is a chemical that

cannot be tasted by some individuals. cannot be tasted by some individuals. – Tasting is dominant to the inability to taste PTC.Tasting is dominant to the inability to taste PTC.

Dominant/Recessive Human Dominant/Recessive Human TraitsTraits

Tongue rolling Tongue rolling – Ability to form a tube Ability to form a tube

with your tonguewith your tongue– Rolling is dominantRolling is dominant

Widow's peak Widow's peak – A sharp point in the A sharp point in the

hairline that points hairline that points toward the nosetoward the nose

– Having a widow's Having a widow's peak is dominant to peak is dominant to a smooth hairlinea smooth hairline

Specific Human TraitsSpecific Human Traits Dimples Dimples

– Round indentations in the cheeks Round indentations in the cheeks when smiling, not lines or cleftswhen smiling, not lines or clefts

Freckles Freckles – Small patches of darker Small patches of darker

pigmented skin on various parts pigmented skin on various parts of the bodyof the body

– These may be present on both These may be present on both dark and light skinned dark and light skinned individuals.individuals.

Hair whorling Hair whorling – These may be referred to as These may be referred to as

cowlicks. cowlicks. – Areas in which hair grows from Areas in which hair grows from

your scalp in a whorl instead of in your scalp in a whorl instead of in a given direction.a given direction.

Specific Human TraitsSpecific Human Traits

Myopia Myopia – Short sightedness, the Short sightedness, the

inability to see far off objects inability to see far off objects without correction by glasses without correction by glasses or contactsor contacts

Polydactyly Polydactyly – Having more than five digits Having more than five digits

on each hand and foot.on each hand and foot.

Specific Human TraitsSpecific Human Traits

S-methyl S-methyl thioester smeller thioester smeller – S-methyl thioesters are S-methyl thioesters are

produced in the urine after produced in the urine after consumption of asparagus. consumption of asparagus. Some individuals cannot smell Some individuals cannot smell this substance. If you smell a this substance. If you smell a strong odor on urination after strong odor on urination after eating at least 5 asparagus eating at least 5 asparagus spears, you are an S-methyl spears, you are an S-methyl thioester smeller.thioester smeller.

White forelock White forelock – A white patch of hair at the A white patch of hair at the

front of the scalp.front of the scalp.

Multiple AllelesMultiple Alleles Determined by more than Determined by more than

one geneone gene Example: eye color Example: eye color

Eye color is determined by Eye color is determined by two genestwo 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 relative A second determines relative abundance of melanin. abundance of melanin.

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

Multiple AllelesMultiple Alleles Hair color is determined Hair color is determined

by more than one geneby more than one gene Thus hair color appears Thus hair color appears

to vary on an almost to vary on an almost continuous scale from continuous scale from black to brown to blond black to brown to blond to redto red

The brown and black The brown and black pigment is melaninpigment is melanin

The red pigment is an The red pigment is an iron containing iron containing moleculemolecule