Heredity
Heredity Benchmarks
III.3.MS.1 - Describe how the
characteristics of living things are passed
on from generation to generation.
III.3.MS.2 – Describe how heredity and
environment may influence/determine
characteristics of an organism.
Breaking down the Benchmarks

III.3.MS.1 - Describe how the characteristics of
living things are passed on from generation to
generation.
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

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Chromosome
Gene
Hereditary information
Common traits controlled by a single gene pair.
• Wrinkled or smooth seeds in a pea plant
• Color of horse hair
• Human traits such as tongue rolling
Breaking down the Benchmarks
– Describe how heredity and
environment may influence/determine
characteristics of an organism.
 III.3.MS.2
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Inherited Traits
Acquired Traits
Heredity Basics
 Heredity
is the passing of traits from
parent to offspring (children).
 The traits are controlled by genes.
 The genes are the chemical code found
in helical (spiral-shaped) molecules of
deoxyribonucleic acid (DNA), which are
packed away inside the cells of all
living things.
Inherited Traits

Inherited traits are those present in the
genetic makeup of an organism that have
been passed on from one generation to the
next. These may include:
•
•
•
•
Eye color
Left- or right-handedness
Butterfly wing patterns
Animal fur color
Acquired Traits



Acquired traits develop or occur after an
organism is born.
They occur in response to environmental
factors such as stress, overall health,
nutritional choices, chemical exposure, and
changes in land use and are not a result of
the organism’s genetic code.
These include:
• Straightened teeth from wearing braces
• The loss of a limb in an accident
Chromosome
 There
are several lengths of DNA in a
cell’s nucleus.
 Each
one is called a chromosome.
Chromosome
 There
are two copies of each
chromosome in every cell of an
organism.
 One
set of chromosomes comes from
the mother and one comes from the
father.
Gene
A
gene is one area of a chromosome
that has the instructions to make one
protein.
 DNA works
by telling a cell how to
make the many different proteins that
your cells need to work.
Gene
 Each
DNA molecule forms a threadlike
structure, or gene. Genes then in turn
form chromosomes.
 There
are two copies of each
chromosome--one from the father and
one from the mother.
Hereditary Information
 We
are all familiar with the idea that
traits can be inherited from parent to
child.

For example, think of dogs: a purebred
pair of Great Danes would never produce
puppies with the tiny, short-legged
characteristics of a dachshund -- but what
does that really mean?
Hereditary Information

Traits are inherited because discrete units
called genes are passed from parent to child
when the child is conceived.

These genes are a unique blueprint for an
individual organism, providing all the
biological information needed for its prebirth development and life, as well as for the
characteristics that make that individual
unique.
Hereditary Information
 Just
as in an engine,
where the removal of
one part can disrupt
the entire engine's
ability to run, so the
removal of the
influence of one gene
can have a severe
effect on the life of an
organism.
Gregor Mendel

In the 1800s Gregor
Mendel an Austrian
monk studied how
traits were passed
from one generation
to the next.

He experimented
with plants (green
peas).
How do we know genes exist?

He kept careful track of the traits displayed by
the pea plants produced by cross-fertilization,
discovering that traits of the parent plants were
inherited by the progeny plants in specific
patterns.
Gregor Mendel

Examination of the trait
inheritance patterns of
the pea plants
suggested to Mendel
that each trait resulted
from two units of
inheritance.

Mendel proposed that
one unit came from
each parent plant.

We now call these units
genes.
Gregor Mendel

The study of how
different forms of a
gene affect
generations of
offspring is
genetics.

That is why Mendel
is called the father
of genetics.
Gregor Mendel

Mendel also learned that a particular trait
could have several varieties that were
produced by different versions of the "units
of inheritance" or genes.


For example, the pea plant flower color could be
pink or white.
We use the term allele to designate a version
of a gene.
Gregor Mendel
 Mendel's
experiments showed that
some alleles appeared to be dominant
over others.

For example, if a pea plant inherits one
pink flower color gene and one white
flower color gene, the resulting flowers will
all be pink -- just as if the plant had two
pink flower color genes. (Pink is the
dominant flower color in peas; white is the
recessive flower color.)
Gregor Mendel
 If
a gene was not dominant then it
could be


recessive
or even a blend.
Genotype/Phenotype
 Two
other concepts that are useful in
understanding genetics are…


phenotype
and
genotype.
Genotype/Phenotype
 The
phenotype of an organism is its
observable traits, and these traits are
produced by the organism's genotype - or genes -- for that trait.

For example, the pea plant with one pink
and one white flower gene has the
genotype pink/white (one pink gene and
one white gene) while its phenotype is
pink (only pink flowers are observed).
Genotype/Phenotype
 Again…in
simpler terms…

Genotype-What the gene says

Phenotype-What you see
Homozygous/Heterozygous

Homozygous pairs of chromosomes have the
same gene for a given trait.


For example, if the gene for brown eyes is B, then the
homozygous pair would be (BB).
Heterozygous pairs of chromosomes have
different versions of a gene for a given trait.

For example, if the gene for brown eyes is B, and the
gene for blue eyes is b, then the heterozygous pair
would be (Bb).
Homozygous/Heterozygous
 Homozygous


gene pair-
Same
(BB) (bb)
 Heterozygous


Different
(Bb)
gene pair-
Punnet Square
Inference and Analysis

Genetics is an elegant and indirect science,
but it is very powerful. In genetics, inference
plays a critical role.


Mendel's experiments led him to infer the
existence of genes, but he never actually saw
them.
Similarly, analysis of mutations, or defects,
in genes help scientists infer normal gene
function.
Inference and Analysis
 By
seeing what happens to organisms
when the function of a gene is
changed, scientists can make educated
guesses regarding what the normal job
of the gene is in the cell.
What kinds of jobs do genes do?
 Genes
are responsible for all the
functions of the cell and are used
throughout the life of an organism.
How does Heredity affect You?

Imagine the phone ringing. Pick it up. Put it to
your ear. Notice which ear you are using.
 Interlock your fingers. Notice which thumb is
placed on top. Pull your hands apart and repeat
the process in reverse order. Notice how
difficult/awkward it is to have the opposite thumb
on top.
 Cross and re-cross your arms. Notice which is
the dominant way you cross your arms.
What other traits have been passed
on to you?
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Handedness (right vs. left)
Eye color
Rolling your tongue in a "U" shape
Free or attached ear lobes
Widow’s peak ("V" hairline on forehead)
Hair on fingers between first and second
knuckle
Cleft chin
Let’s Chart It!
 Wow!!
We have inherited a lot of different
traits.
 Let’s
collect the data and record it in a
chart, so that we can better understand
that our individual traits are a blend of our
parents genetic information.