Biology - Patterns of Inheritance
Inheritance

______________________________________is the scientific study of
heredity.

A ____________________________________ is a characteristic that is
passed from parent to offspring (ex. Eye color).

The _________________________________________ hypothesis was once
believed to be the way traits were inherited from generation to generation.
Think mixing paints. This is the idea that each generation is a mix (or
blend) of both parents genes (traits). This does not account for the
appearance of unexpected traits.

Traits are passed to _____________________________________________
through chromosomes.
Gregor __________________________________________, an Austrian Monk, (1860’s)
studied the pea plant.

He knew nothing of _________________________________________
biology (or chromosomes).

He did NOT support the blending hypothesis, and in fact,
__________________________________________ it through his studies.

He is the __________________________________________ of genetics.
Mendel used the pea plant for 3 reasons:
1. The structure of the pea flowers allowed:

__________________________________fertilization (which means the plant
can breed with itself, a process called ________________________________
breeding)

OR he could ____________________________ pollinate the flowers and
produce a _______________________________________________ (this is
an organism that receives different forms of a genetic trait from each
parent, or 2 sets of DNA: 1 from each parent).
2. The _____________________________________ reproduction cycle: the pea plant
reproduces about every 90 days.
3. The presence of
______________________________________________________________ allowed Mendel
to observe his results easily. He studied 7 traits (we will look at 5). Traits in the pea plant
have only 2 forms (there is NO intermediate or in between form; it is either/or):
Purple (P) vs. white (p)= flower color
Yellow (Y) vs. green (y)= pea color
Round (R ) vs. wrinkled (r )= pea shape
Green (G) vs. yellow (g)= pod color
Tall (T) vs. short (t)= height
Mendel’s Observations:

When Mendel worked with the pea plants he used 2 different groups of
___________________________________________ plants, looking at 1 trait at a
time.
o For example, he used 1 group of purebred purple flower pea plants & 1 group
of purebred white flower pea plants.

He crossed these 2 groups with each other
(________________________________________________ them) and called them the
parental generation, or ________________.
o This is a _____________________________________ cross (crossing 1 trait).

All of the offspring had _______________________________ flowers.

This generation did not show up as a blend of parents (no mix b/c they are not less
purple). But, where did the white flower trait go?
o He called this generation of offspring the First Filial or
______________generation (filial refers to
________________________________________).
o The offspring is a ________________________________________ of the
parents.

He allowed the F1 generation to _________________________________________.
He called this generation the second filial, or ________________________generation.
o The F2 offspring revealed 3 out of 4 had purple flowers and 1 out of 4 had
white flowers. Again, no blending resulted. Also, the white flower trait had
______________________________ disappeared.

Mendel performed this experiment with all 7 traits and received the same results: the
offspring is not a mixture of the parents; the original traits do not disappear.

In his work, all F1 revealed 1 characteristic: this characteristic is dominant. All F2
generations were in a 3:1 ratio (3 dominant: 1 recessive).

_______________________________________ are sections of a chromosome that
code for a trait.

Most organisms have __________________ copies for every gene and chromosome
(1 from each parent).

An _____________________________________ is a distinct form of a gene.

If an organism has 2 different alleles for 1 trait, only 1 allele is expressed or
_____________________________________ (usually).

The ______________________________________________allele is a form of a gene
that is fully expressed when 2 different alleles are present.
o This is represented with a ___________________________________ letter
(and is written 1st).
o Ex. Purple= P

The _______________________________________________allele is a form of a gene
that is not expressed when paired with a dominant allele (it takes 2 recessives to be
expressed).
o This is represented by a ____________________________________ case letter
& is written 2nd.
o Ex. White= p
The ________________________________________________ Theory of Heredity (developed
by Walter ____________________________________) states that the material of
inheritance is carried by the genes in the chromosomes.

A ____________________________________________ is the genetic makeup of an
organism. Ex: GG, Gg, gg or BB, Bb, or bb

A phenotype is the ______________________________________ expression of the
genotype or the outward expression of that trait. Ex: yellow peas.

____________________________________________ is having 2 of the same alleles (2
identical alleles). Ex: GG or gg

____________________________________________ is having 2 different alleles. Ex:
Gg
Mendel’s Laws:
These are the Rules of inheritance:
1. The Law of ___________________________________________________:
Gene pairs ___________________________________________ when gametes form.
This means: genes (alleles) are on chromosomes; chromosomes separate during meiosis;
gametes form during _______________________________________; therefore, genes
separate when gametes form.
2. The Law of _______________________________________________ Assortment:
When looking at 2 traits at the same time, it is seen that
_________________________________________ are inherited
__________________________________________________________ from each other.
Gene pairs segregate into gametes randomly and independently of each other.
Genetics & Predictions:

In genetics we use mathematical _________________________________________(P).
If you flipped a coin what are the chances of it landing on heads?
o P= ½ or 50%

If you flipped a coin 10X what would you expect the chances of it landing on heads?
o About 5 times or 50% or ½ or 1:1 (ratio)
o In science, we generally use the ratio.

A ____________________________________________ square is used to organize &
predict genetic information.
Let’s use Mendel’s purebred purple flowers & purebred white flowers:
PP X pp
Always show the cross
Set up square
Genotype= 4Pp
Always use ratios!
Phenotype= All Purple
Use WHOLE #s (no
fractions)!
Let’s cross the F1 generation.
Pp X Pp
Genotype= 1PP: 2Pp: 1pp
Phenotype= 3 purple: 1 white
Now you have some practice problems!
What happens if we have a purple flower but we don’t know if it is heterozygous or
homozygous? How would we figure out what it is?

We would perform a __________________________________________. This is a
cross between a recessive organism (in this case a white flower because we know the
genotype) with an organism that has an unknown genotype (the organism that is
showing the dominant phenotype) in an attempt to discover the
_______________________________________ of the unknown.

If the offspring result in a recessive organism then the unknown parent must be
___________________________________________.
Variations in Inheritance:
_______________________________________ dominance is what Mendel saw. One trait is
completely dominant (expressed) over another. Either/or; dominant or recessive. Purple
flowers or white flowers.
Intermediate Inheritance:

Not all genes are cut and dry; one allele is not always clearly dominant over another
& there are not always just 2 distinct forms in nature.

__________________________________________________ inheritance is when the
heterozygous offspring has its own trait (different than either parent). This is not
seen in pea plants. This includes __________________________________ & incomplete
dominance.

__________________________________________ dominance is when there is a
heterozygote BUT neither the dominant or recessive allele is completely expressed.
Look at snapdragons.
o A red snapdragon (RR) is crossed with a white snapdragon (rr).
o As you would expect, the F1 generation is Rr BUT they are not Red, they are
PINK!
o This almost looks like the blending hypothesis, right? But it is not. Why??
Allow the F1 generation to self-fertilize.
Rr
X
Rr
The genotypic results are 1RR: 2Rr: 1rr
The phenotypic results are
1 red: 2 pink: 1 white

The original traits are ___________________________ lost; therefore this is NOT
the blending hypothesis.

An example of incomplete dominance in humans is hypercholesterolemia (having too
much _____________________________________ in the blood).

______________________________________________is seen when there are more
than 2 alleles for 1 trait and 2 different dominant alleles are together but neither
dominant alleles overpower the other.
o This is seen in human blood types.
There are 4 blood types in humans: type _____________, ____________________________,
type AB, and type O. These are phenotypes!

________________________________________ for blood types in humans are
represented with the letter I.

A
B
I represents A, I represents B, and i represents _____________________.

Codominance is human blood types is phenotypically represented by type AB and
A B
genotypically represented by I I .

____________________________________ traits are when traits are affected by
more than 1 gene.
o Eye color, __________________________ color & skin color are examples of
polygenic traits.

_________________________________ alleles are when there are more than 2 alleles
per trait.
o Again human blood types are examples.

________________________________________ is when 1 gene affects more than 1
trait. An example of this is
__________________________________________________ or sickle cell disease.
This affects the shape of red blood cells (RBCs).
o RBCs are normally _________________________________________.
o In sickle cell anemia, they are _________________________________-moon
shaped (sickle shaped).
o This __________________________________________ normal blood flow
through blood vessels causing circulatory system damage, weakness, anemia,
brain damage & other organ damage.
Chromosomal Theory of Inheritance

Specific genes are located on specific chromosomes, or have
_______________________
Genetic Linkage

Genetic linkage (or _________________________________________) genes that are
located on the same chromosome.

Generally, these genes will be ____________________________________________.

The closer these genes are on a chromosome, the
_________________________________ the chances are that they will be inherited
together.

Thomas _________________________________________ worked with
________________________________________________ (Drosophila melanogaster)
and discovered linked genes.
Sex-Linked Traits

_______________________________ chromosomes determine the sex of the
organism. In humans, XX is female; XY is male.

__________________________________ are non-sex chromosomes.

_______________________________________ traits are genes that are located on the
X or Y chromosomes. There are more genes on the X than the Y.
Sex-linked Traits in Humans:

_______________________________________________ is recessive and found on the
X chromosome.
o This is when someone cannot see ______________________ or
_____________________________.
o _____________________________ males suffer from this than females.

Hemophilia is recessive and X-linked also.
o This causes excessive _______________________________ and no normal
blood clotting.
o More males suffer from this than females.
FYI: Environmental Effects:
External & internal environmental conditions can affect genetic expression.
Some examples:

Environmental temperature affects the Himalayan rabbit’s fur coat & the
western white butterfly’s wing coloration for flight.

Soil _________________________________ affects the color of hydrangeas
(acidic=blue; neutral=pink)

Japanese _____________________________________ changes sex in
response to social environment
Nature vs Nuture:
Study of identical twins that were separated at birth & brought up differently revealed
that there are genetic links between individuals. The results of the studies revealed that
these twins had similar likes, dislikes, opinions, etc.