Transcript genetic trait inventory

GENETIC
TRAIT
INVENTORY
These are the traits that have been passed on to
you by your parents…
BENT PINKY FINGER
• There are people who have a pinky finger that turns inward toward
the fourth or ring finger. Some people with this condition do have
crooked bones, but the finger still appears straight like a normal
finger. A crooked little finger is also known as,
clinodactyly. Clinodactyly is a Greek term for "bent digit," and is used
to describe a bent finger or even toe. It is actually a rare disorder,
affecting 10% or less of the population.
COLORBLINDNESS
• Red-green colorblindness is caused by a single gene located on the Xchromosome. This gene codes for a protein in the eye that detects certain colors
of light. When this gene is defective, the eye cannot differentiate between red
and green.
• You need at least one working copy of the gene to be able to see red and green.
Since boys have just one X-chromosome, which they receive from their mother,
inheriting one defective copy of the gene will render them colorblind. Girls have
two X-chromosomes; to be colorblind they must inherit two defective copies, one
from each parent. Consequently, red-green colorblindness is much more frequent
in boys (1 in 12) than in girls (1 in 250).
• Red-green color blindness follows a very predictable recessive, sex-linked
inheritance pattern. A woman with one defective copy of the gene and one
functional copy, even though she is not colorblind herself, is known as a "carrier."
She has a 50% chance of passing the defective copy to each of her children. Half
of her sons will be colorblind, and half of her daughters will be carriers.
DARWIN’S EAR POINT
• The dominant "Darwin's" earpoint gene results in the inside curve
of the uppermost ear fold to have a crease or angle to it. Recessive
individuals have a very rounded inside curve of the uppermost ear
fold.
DIMPLES
• Dimples are small, natural indentations on the cheeks. They can
appear on one or both sides, and they often change with age. Some
people are born with dimples that disappear when they’re adults;
others develop dimples later in childhood.
• Dimples are highly heritable, meaning that people who have dimples
tend to have children with dimples—but not always. Because their
inheritance isn't completely predictable, dimples are considered an
“irregular” dominant trait. Having dimples is probably controlled
mainly by one gene but also influenced by other genes.
EAR LOBES
• If earlobes hang free, they are detached. If they connect directly to
the sides of the head, they are attached. Earlobe attachment is a
continuous trait: while most earlobes can be neatly categorized as
attached or unattached, some are in-between.
• Although some sources say that this trait is controlled by a single
gene, with unattached earlobes being dominant over attached
earlobes, no published studies support this view. Earlobe attachment
and shape are inherited, but it is likely that many genes contribute to
this trait. As such, its pattern of inheritance is difficult to predict.
EYE COLOR
It turns out that eye color and most hair colors are way too complicated
to be simple dominant/recessive traits. Surprisingly, blue-eyed parents
sometimes have a brown-eyed child. Now this isn't that common so we
could still say that blue eyes are mostly recessive. The same isn't really
true for blonde hair.
FRECKLES
• Freckles are small, concentrated spots of a skin pigment called
melanin. Most fair-skinned, red-haired people have them.
• Freckles are controlled primarily by the MC1R gene. Freckles show a
dominant inheritance pattern: parents who have freckles tend to
have children with freckles.
• Variations, also called alleles, of MC1R control freckle number. Other
genes and the environment influence freckle size, color, and pattern.
For example, sun exposure can temporarily cause more freckles to
appear.
HAIR COLOR
• All humans have some pheomelanin in their hair. Eumelanin, which
has two subtypes of black or brown, determines the darkness of
the hair color. ... According to one theory, at least two gene pairs
control human hair color. One phenotype (brown/blonde) has a
dominant brown allele and a recessive blond allele.
HAND CLASPING
• Without thinking about it, fold your hands together by interlocking
your fingers. Which thumb is on top—your left or your right?
• One study found that 55% of people place their left thumb on top,
45% place their right thumb on top, and 1% have no preference. A
study of identical twins concluded that hand clasping has a strong
genetic basis (most twins share the trait), but it doesn’t fit a
predictable inheritance pattern. It is likely affected by multiple genes
as well as environmental factors.
HITCHIKER’S THUMB
• Hitchhiker's thumb does not come about by spending hours on the
freeway waiting for a lift. It is a recessive genetic trait that allows
people to bend their digit into an unusual shape.
MID DIGITAL HAIR
• Some people have hair on the back of the middle segment of some
fingers. Individuals with hair on the middle segment of at least one
finger are considered to have the trait mid-digital hair
PTC PAPER
• To about 75% of us, the chemical PTC (phenylthiocarbamide) tastes
very bitter. For the other 25%, it is tasteless. The ability to taste PTC is
controlled mainly by a single gene that codes for a bitter-taste
receptor on the tongue. Different variations, or alleles, of this gene
control whether PTC tastes bitter or not.
• PTC tasting follows a very predictable pattern of inheritance. Tasting is
dominant, meaning that if you have at least one copy of the tasting
version of the gene, you can taste PTC. Non-tasters have two copies
of the non-tasting allele.
• To learn more, visit PTC: Genes and Bitter Taste.
TONGUE FOLDING
• Can you roll your tongue? If so, you’re part of the majority.
Between 65 and 81 percent of people on Earth have this strange and
seemingly arbitrary talent. But why can some do it while others can’t?
The most common answer, the one often taught in elementary
schools and museums, is that it’s all about genetics. The story goes
that, if you inherited a dominant variation of the “tongue rolling
gene” from one of your parents, you too will inherit this party trick. In
other words, if you can’t do it, blame mom and dad.
TONGUE ROLLING
• Some people can curl up the sides of their tongue to form a tube
shape. In 1940, Alfred Sturtevant observed that about 70% of people
of European ancestry could roll their tongues and the remaining 30%
could not.
• Many sources state that tongue rolling is controlled by a single gene.
However, as Sturtevant observed, people can learn to roll their
tongue as they get older, suggesting that environmental factors—not
just genes—influence the trait. Consistent with this view, just 70% of
identical twins share the trait (if tongue rolling were influenced only
by genes, then 100% of identical traits would share the trait).
WIDOW’S PEAK
• If your hairline forms a point at the center of the forehead, you have a
widow's peak. If not, you have a straight hairline. While some sources
say that widow’s peak is a dominant trait controlled by one gene, no
scientific study supports this claim. Complicating the question of
heritability is the fact that the trait is continuous: some people have
just a slight suggestion of a peak.
• Widow's peak is likely controlled by genes rather than the
environment. But while hairline shape tends to run in families, its
pattern of inheritance is usually unpredictable, suggesting that
multiple genes are involved.