
Your genes, located
on your
chromosomes
contain dominant
and recessive traits
which were
inherited from your
parents and
grandparents.

Some of your
characteristics
are caused by
only one gene
from each
chromosome.



Traits that show themselves over recessive or
hidden traits
Remember that genes come in pairs- if only
one is dominant the organisms will show that
trait
Examples: Tongue rolling, Detached
earlobes



Traits that are masked or hidden by a
dominant trait
Genes come in pairs- if only one is recessive
it will not be expressed in the individual
Examples: Attached earlobes, straight thumb



Gregor Mendel
Austrian Monk
Experimented with
pea plants and
noticed that they
contained “factors”
that were passed to
offspring.

Dominant

Recessive- you must
have two genes to have
this trait


Detached Earlobes are
dominant- only one
gene of the pair
necessary
Attached- recessive
Hitchhikers' ThumbDominant
Straight ThumbRecessive
Index Longer than RingDominant
Ring Longer than IndexRecessive
Peak- Dominant
Straight- Recessive
Counter-ClockwiseRecessive
Clockwise-Dominant
Homework Solutions
B
b
B
b
____%white
2. Black fur (B) in guinea pigs is
dominant over white fur (b). Find the
probability of a hybrid offspring in the
cross: BB x Bb
B
B
B
_______% hybrid
b
3. Black fur (B) in guinea pigs is
dominant over white fur (b). Find the
probability of a purebred offspring in
a cross: BB x BB
B
B
B
_____% purebred
B
4. bb x bb
b
b
b
_________% black
b
5. Find the probability of an offspring with the
same phenotype as its parents in a cross between
a purebred
black and a hybrid black guinea pig.
_____% same phenotypes as parents
6. Bb x bb
B
b
b
__________% white
b



Two traits combine or blend together to
produce a different trait.
There is no dominant or recessive trait.
Instead, both traits have about the same
influence on the organism.
Use different letter for each trait:
bb= black ww= white bw=gray
BB x WW = BW
RR or BB x WW= RW or BW
RR x WW = RW