Download Heredity: Life Goes On

Heredity Shared Read #1
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 **
What unique traits have you inherited?
Heredity Shared Read #2
How Characteristics Are Inherited
Have you ever walked through a flower garden and noticed the many
different sizes, shapes, colors, and textures of flowers? These flowers contain the
parts necessary for reproduction among their species. Flowers trade sweet
nectar and protein-rich pollen in return for pollination service provided by insects
and other creatures. For many plants, the production of seeds, which are their
offspring, depends on the transfer of pollen from one flower to another flower of
the same kind. One pollinator, the honey bee, has many little hairs on its body
which collects pollen as the bee visits flowers. Some of this pollen brushes off as
the bee visits other flowers. This process of pollination enables one parent plant
to transfer information about its traits to the other parent plant, and thus to their
offspring.
Gregor Mendel, a monk and a scientist, also known as the “father of
genetics” spent much of his time working with plants in a garden. He observed
that some pea plants were tall while others were short. He also observed that
some plants produced green peas and others produced yellow peas. He knew
traits were inherited, but he didn’t understand how.
In 1857 Mendel began experimenting by crossbreeding different pea
plants. He kept detailed records of his results, which were published in 1865.
Mendel first bred a tall pea plant with a short pea plant. All the offspring,
the first generation, were tall plants. He then bred two of these tall plants. In the
second generation, three-fourths of the offspring were tall and one-fourth were
short.
Mendel hypothesized that every trait is controlled by a pair of factors. For
each trait, an offspring inherits one factor from each parent. The way the factors
combine determines which trait appears in the offspring.
In peas, tallness is a strong trait, or dominant trait. Shortness is a weak
trait, or recessive trait. Factors for both dominant and recessive traits may
occur in an organism’s chromosomes. However, recessive traits can be seen only
if both parents pass the factor for it to the offspring. If only one parent pea plant,
for example, passes a factor for shortness, the factor remains hidden. Then none
of the offspring are short.
Punnett Square
Chromosomes are tiny, threadlike structures inside most cells of every
organism, or living thing. Chromosomes carry information about the
organism in units called genes. When living things reproduce, they pass
their genes along to their offspring. Each parent has 23 chromosomes.
Maternal
Maternal
Paternal
Grandma
Grandpa
Grandma
MOM
Paternal
Grandpa
DAD
Offspring
Maternal
Maternal
Paternal
Grandma
Grandpa
Grandma
MOM
DAD
Offspring
Who is the father of genetics?
Paternal
Grandpa
Heredity Shared Read #3
Life Cycles
Sometimes, offspring do not look like the parent organism. However, as
they go through their life cycles (the stages a living organism will go through
during its life time) they begin to look more like their parents. For example, the
legless little tadpole with its large tail looks very different from what it will look
like as a full grown frog
Life Cycle of a Frog
The pale, segmented mealworm changes dramatically as it goes through its
life cycle to become a darkling beetle.
Egg-white, oval-shaped eggs will hatch into the worm-like larva.
Larva (mealworm) – the tan /brown larva looks like a worm, but has 6 legs and 2
antennae. It will molt many times as it grows.
Pupa-the white/cream pupa has a large head and a pointed tail. The adult will
emerge from the pupa.
Adult-the adult is the dark brown darling beetle.
Variations
Compare puppies in a litter. Even though these puppies may have had the
same two parents, there are variations in how they look and act. Variations are
the differences in the appearance of an inherited trait among the members of a
group (species). The difference in a paw size, tail length, or fur coloring are
examples of variations. Some variations do not have much of an effect on an
organism. For example, the different colors of fur on puppies may have little
effect on whether or not each puppy will survive.
However, for some organisms living in
the wild, color can make a big difference. For
example, a moth with brightly colored orange
and yellow wings will not survive very long if
its environment is the dark bark of pine trees.
The brightly-colored moth would be easily seen and eaten by birds.
A moth with similar color patterns to its surroundings may
survive longer. These variations give a species, (a certain
group of plants or animals that can only reproduce among
themselves) a better chance to live or survive.
There are many variations in plants. For
example, there are many variations of corn. Most
corn stalks look alike while it is growing, but there is
great variation in the seeds and the “ear” of corn.
This is a picture of sweet corn
variations. This is the corn
you like to eat.
Indian Corn
What does variation mean?
Heredity Shared Read #4
Instincts and Specialized Structures
Instincts are also behaviors that are inherited (not taught) from the
parent organism. These instincts help organisms to survive. This explains why
salmon migrate upstream to spawn, a cat purrs, a duck swims, a spider spins a
web, or a termite rots wood
Other variations may include specialized structures for organisms to survive
in their environments. Environment is the surroundings in which an organism
lives. A specialized structure is a body part unique to a species for survival
in its environment. A snowshoe rabbit has small ears and broad feet. Its smaller
ears prevent it from losing body heat, enabling it to stay warmer in its cold
northern habitat. Its broad-sized feet are well suited to help it travel over snowy
terrain.
Snowshoe Rabbit
Jackrabbit
A jackrabbit lives in the hot, dry areas of the southwest. It has long, large
ears and powerful hind feet. These ears provide a large surface area that allows
excess heat to escape. The powerful hind legs enable it to outrun predators.
These specialized structures of the snowshoe rabbit and the jackrabbit enable
them to live and reproduce in different environments.
A crane has large, feet enabling it to walk and stand in
muddy, shallow ponds. Its long legs raise its body well above
the water, to give it a good view of animals swimming below.
The crane can quickly stretch out its long neck to grab its
prey with a quick snap of its sharp beak.
Another animal with a specialized structure is a bird. All birds have a beak
but all beaks do not look the same. A goldfinch has a short beak for eating seeds.
A woodpecker has a slender beak to get insects from under tree bark. A hawk has
a hooked beak for ripping and tearing prey, such as rabbits.
Goldfinch
Woodpecker
Hawk
Variations among plants can also provide them with a survival advantage.
Pine seedlings compete for sunlight, water, and soil nutrients. Fast-growing
seedlings are more likely to crowd out their slow-growing neighbors. Most
organisms compete for resources such as food, air, water, and space. Variations
that make it easier for organisms to find or use a resource are better able to
survive.
The environment is constantly changing. Sometimes the changes are
gradual, as in climate changes. Other changes may be sudden, such as volcanoes,
earthquakes, floods, landslides, or violent storms. When an environment
changes, some organisms die. Some organisms move to a new environment.
Some have variations for better survival (the continuation of life). The helpful
variations will be inherited by some of the offspring. After many generations,
most organisms in that species will have those helpful variations. Years ago,
when DDT (a poison that kills insects) was used on the environment, a few
mosquitoes were resistant to DDT. Mosquitoes with this variation were better
suited to survive in an environment that contained DDT. They lived and produced
offspring that DDT could not kill. As a result, the population (the number and
kind of organisms in an area) of DDT-resistant mosquitoes has grown larger in
recent years.
Learned Behaviors
The traits inherited from parents are only part of who the organism is.
Some actions of organisms are learned behaviors from parent organisms and
from their environment. A learned behavior is an action that is learned
through trial and error or is brought about by the environment. These are
behaviors learned during an organism’s lifetime. Learned behaviors vary from
organism to organism. Calves, following their mothers to the water troughs, will
soon learn to go there by themselves when they are thirsty. Dogs learn different
ways to let their owners know when they want to come inside or go outside the
house. Some dogs may scratch at the door while others may sit by the door and
whine. Many animals such as bears develop different ways of hunting food.
Some grizzly bears hunt salmon by grabbing at the fish from the shoreline with
their powerful paws. Other grizzly bears dive into the river and use their strong
jaws to catch salmon.
Trees and plants will bend toward the sun to get the sunlight they need for
survival. Trees, such as those on high mountains or near sea shores, may also
bend away from constant blowing winds.
Learning is important for all organisms because it allows them to change
when the environment around them changes. This ability to change or learn a
new behavior will help them to survive for many years.
Name a learned trait of a grizzly bear.
Why do birds have different types of beaks?