Heredity: Life Goes On
Look around and see all the people in your life: your friends, your
family, your neighbors and your classmates.
Now take another look at the people you don’t know: people you see in
the airport, the shopping mall, or at a football game. Then think of the number
of people who live in different towns and cities throughout your state, the
country, and the world. Try to imagine all the billions of men, women, and
children who make up the human population that are living on this planet
right now. Each individual has characterisitcs that are similar to the whole
group, some characteristics that are similar to a particular group, and some
that are uniquely his/her own.
Not only people are unique, but all life forms. Some trees grow very tall
with thick bark while others are very short with thin bark. It all depends on
an organism’s heredity, the passing of traits from parents to their young.
An organism is any living thing that can carry out its life activities on its
own. Heredity applies to all organisms including humans, animals, plants,
insects, and even bacteria.
Inherited Traits
In a pond, every frog is unique because of various traits it inherited from
its parents. A trait is a characteristic that determines how an organism
looks, acts, or functions. An inherited trait is a characteristic passed
from parents to their young. Some examples of inherited traits are fur color,
stripes, or spots. The big cats pictured below show inherited traits. Can you
see similarities and differences between the two cats?
Dogs will always have puppies, just as cats will always have kittens, and
acorns will always grow into oak trees. That is why people are alike in most
ways. We have noses in the middle of our faces and not on the backs of our
heads, as dolphins do. We have eyes in the front, and not on the sides of our
faces, as rabbits do. We have neither a tail like a dog, nor a neck like a giraffe.
We look like people!
All organisms are made up of small building blocks. A person consists of
about ten trillion of these building blocks, which come in over 200 varieties.
These building blocks give organisms their individual traits and vary from
organism to organism. These small differences are enough to keep organisms
from looking identical. These differences establish our color of hair or eyes,
whether we are tall or short, and whether we have freckles or not. Each of us
has inherited our own mixture of traits. Within each building block are
special instructions that tell an organism how it will grow and what traits it
will develop.
Parent organisms (a producer of offspring) pass these instructions to
their offspring, the young of an organism.
For example, a puppy may inherit its fur color from its mother; a seedling may
develop wide, broad leaves from its parent plant; or human beings may
inherit a variety of traits. A few of these inherited traits include:
In 1940, the famous geneticist
Alfred Sturtevant noted that about
70% of people of European
ancestry are able to roll up the
lateral edges of the tongue, while
the remaining 30% were unable to
do so.
Most people have a “widow’s
peak” hairline while others
have a straight hairline.
More people have unattached earlobes
or “free earlobes” than attached
earlobes.
If earlobes hang free, they are detached. If
they attach directly to the side of the head,
they are attached earlobes.
The size and appearance of the lobes are also
inherited traits.
Some people have freckles on their skin.
This trait is reportedly due to a single
gene; the presence of freckles is
dominant, the absence of freckles is
recessive.
Cleft Chin
This trait is reportedly due to
a single gene with a cleft chin
dominant and a smooth chin
recessive.
Dimples are reportedly due to a single gene
with dimples dominant (people may
exhibit a dimple on only one side of the
face) and a lack of dimples recessive.
Hitchhiker thumb: More people (6475%) have a straight thumb than a
curved hitchhiker thumb.
Naturally Curly
Hair vs. straight
Early geneticists
reported that
curly hair was
dominant and
straight hair was
recessive. More
people have curly
hair.
Hand Clasping
Fold your hands together by
interlocking your fingers without thinking
about it. 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.
Colorblindness
8% of males are color blind
92% of males have normal vision
100% of women have normal vision
Colorblindness is due to a recessive allele located on
the X chromosome. Women have two X
chromosomes, one of which usually carries the allele
for normal color vision. Therefore, few women are
colorblind. Men only have one X chromosome, so if
they carry the allele for colorblindness, they will
exhibit this trait. Thus, colorblindness is seen more
frequently in men than in women.
Allergies
While allergic reactions are induced by things a person comes in contact
with, such as dust, particular foods, and pollen, the tendency to have
allergies is inherited. If a parent has allergies, there is a one in four (25%)
chance that their child will also have allergy problems. This risk increases if
both parents have allergies2.
Handedness
Some scientists have reported that handedness is due to a single gene
with right handedness dominant and left handedness recessive. However,
other scientists have reported that the interaction of two genes is
responsible for this trait. 93% are right handed – 7% are left handed
Lefty Brain Teasers
Because their brains are organized differently, left-handers see and think
differently and can get some very different results from various "brain tests",
usually doing very well on tests that involve creative thinking or unraveling
complex images and manipulating 3D images. Here's a famous test of
creativity - have a look at the image below:
A non-creative right handed brain sees only a hodgepodge of disconnected
shapes, but the left-handed brain can go beyond logic and find the
connecting concept that makes sense of the shapes. If you can't "see"
beyond the shapes, it's because your right-handed brain is trying to solve
the problem and won't let your left-handed brain have a go. If you still can't
see the picture, the answer is at the bottom of this page **