Download Chapter 7 Growth and Inheritance

Chapter 7 Growth and
Inheritance
Lesson 2:
How Are Characteristics
Inherited?
Vocabulary Preview
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Inherited trait: a characteristic passed from parents to their offspring
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Dominant trait: a trait that appears even if an organism has only one
factor for the trait
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Recessive Trait: a trait that appears only if an organism has two
factors for the trait
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Gene: the part of a chromosome that contains the DNA code for an
inherited trait
Questions to think about!
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Do living things pass on
traits?
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What kinds of traits do
humans have in
common?
Inherited Characteristics Lab
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Procedure: Steps to Follow
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1. Complete the following table like the one shown.
2. Stick out your tongue and try to roll its edges up, toward the
middle.
3. Use your partner to help you make your observation. Record
your results.
4. Use your partner to help observe the shape of your earlobes.
Are they attached to your face or do they hang free? Record your
results.
5. Fold your hands in front of you. Observe which of your
thumbs falls naturally on top. Record your results.
6. Use your partner to help observe whether you have a widow’s
peak or not. Record your result.
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Characteristic
Result:
(Circle One)
Class Totals
Tongue Rolling
Yes
No
Earlobes
Attached
Free
Folded Hands
Left
Right
Widow’s Peak
Yes
No
Draw Conclusions
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1. Which traits in each pair occurred more often
in your class?
2. Do you think these characteristics are
inherited or learned?
http://www.sln.org/guide/knox/Traits/traitsex
amples.pdf
How Characteristics are Inherited?
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You may have a friend who
looks a lot like her parents.
She may share her mother’s eye
color and dimples or have the
same hair and skin type as her
father.
These and many other traits are
inherited.
An inherited trait is a
characteristic passed from
parents to their offspring.
How Characteristics are Inherited?
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In humans, hair color, eye color, and skin color are
inherited.
Freckles, hair texture, and earlobe shape are also
inherited.
So are some behaviors ex. The tendency to be right/left
handed
In animals, eye color, fur color, texture is inherited.
How Are Characteristics Inherited?
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Each of the puppies inherited
some traits from its parents,
including facial shape and
hair texture.
For many years, farmers have
selected animals through
breeding.
They’ve bred animals having
some desirable with animals
having other desirable traits
so that the offspring would
have these traits too.
Dominant and Recessive Traits
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Gregor Mendal an Austrian monk
did hundreds of experiments and
kept careful records of his results.
He found that first-generation
offspring of tall plants and short
plants were tall, but secondgeneration offspring included
about one-fourth short plants.
He hypothesized that the firstgeneration plant must have a
hidden factor for shortness.
How else could this trait appear in
the second generation?
Dominant and Recessive Traits
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In pea plants, tallness is a strong trait, or a dominant trait.
If an organism has one factor for a dominant trait, that trait
appears.
Shortness in pea plants is a weak trait, or a recessive trait.
A recessive trait appears only if an organism has two factors for
the trait.
If both a dominant factor and a recessive factor are present, the
dominant trait appears.
This explains why three-fourths of Mendel’s second generation
pea plants were tall.
Dominant and Recessive Traits
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Plants with one or two factors for tallness were
tall.
Plants with two factors for shortness were short.
Ex: Fur color in mice. 3 of the offspring are
dark brown, and one is light brown.
Both parents have dark brown fur which is
dominant.
For light brown fur to appear, both parents
must have a factor for light brown fur.
You can use a Punnett Square to predict the traits
that offspring will show. In mice, dark brown fur is
dominant. Dominant factors in the square are
capital letters. Here, B is the factor for dark brown
fur, and b is the factor for light brown fur. One
parent’s factors are shown at the top of the square,
and the other parent’s factors are shown at the left
of the square.
You can predict the fur color of the offspring by
pairing each factor from one parent with each
factor from the other parent.
Dominant and Recessive Traits
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In humans, having blue eyes is a recessive trait.
Can two brown-eyed parents have a child with
blue eyes?
Yes, but they must both have a hidden factor for
blue eyes.
Dominant and Recessive Traits
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The ability to roll your
tongue is a dominant trait. If
you can roll your tongue, you
inherited either two
dominant factors (one from
each parent) or one dominant
factor and one recessive
factor.
If you aren’t able to roll your
tongue, you inherited two
recessive factors (one from
each parent).
Dominant and Recessive Traits
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Unattached earlobes are
dominant, and attached
earlobes are recessive.
If your earlobes are
unattached, you inherited
at least one dominant
factor.
If you have attached
earlobes, you inherited
two recessive factors.
Dominant and Recessive Traits
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Even though righthandedness is dominant,
most people rest the left
thumb on top when they
fold their hands.
Resting the left thumb
on top is dominant.
If you rest your right
thumb on top, what
factors did you inherit?
Genes
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Today Mendel’s factors are known to be different
forms of genes.
A gene is the part of a chromosome that contains the
DNA code for an inherited trait.
DNA is a chemical that provides detailed instructions
to the cell about every function of life.
Ex: It directs the cell to divide to make more cells and
to perform various other functions
http://www.sonic.net/~nbs/projects/bio115l/form.ht
ml
Genes
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A gene for a particular trait is found at a specific
place on a chromosome.
All inherited traits-tongue rolling, thumb
position, hair color are controlled by genes.
You are genetically unique. You share some
characteristics with most humans, but unless you
have an identical twin, there is no one else with
exactly the same combination of genes that you
have.
Genes
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What makes you different
from everyone else?
Remember that during
meiosis, each gamete gets
only one half the
chromosomes of a body cell.
So each of your parents
contributed half of his/her
genes to you. You inherit
over 30,000 different genes
which makes you unique.