Mendel and Genetics
• Gregor Mendel was the first
scientist to study genetics
and how traits are passed
from parents to offspring
(children.)
• Mendel bred pea
plants. He was able
to see that some
traits are passed
down to offspring
and sometimes they
skip a generation.
• Mendel studied pea plants
because they have a great
variety of traits, such as
flower color, plant height,
seed shape, seed color, pod
shape, and flower position.
• Pea plants are self pollinating,
which means that they have
both male and female
reproductive parts. The pollen
(male parts) from one plant
can fertilize the eggs (female
parts) from the same plant or
another plant.
• Mendel decided to breed
one characteristic at a
time. He used true-breeding
plants to do so. True
breeding plants will only
produce their trait in their
offspring.
• Mendel also crossed two plants
with opposite traits( for
example, white flower with a
purple flower). This is called
cross-pollination.
• He would take the pollen from
one plant and sprinkle another
plant that had the pollen
removed.
•Mendel conducted
two experiments.
• The first experiment involved
cross pollination.
• He found that one trait always
showed up. He called this trait
dominant.
• The other trait seemed to
disappear. He called this
recessive
• In the second experiment
Mendel allowed each
offspring plant from the
first cross to self pollinate.
• This time the recessive
trait was also seen, not just
the dominant!
• The true-breeding cross is
called the P or parental
generation.
• The offspring of a cross
pollination are called the F1
generation.
• The offspring from a F1 cross
is called the F2 generation.
•
Mendel created a ratio of dominant to
recessive traits to try to determine the
reason for the results.
•
He realized that each parent donates
genes to their children. The genes can
be dominant, recessive (homozygous) or
a mix of both (heterozygous.
•
The two forms of the genes are called
alleles.
• EXAMPLE:
R= dominant gene for red
r= recessive gene that appears white
RR=homozygous dominant, red
rr=homozygous recessive, white
Rr=heterozygous, red
• The actual letters that
represent genes are called the
genotype.
• The physical appearance of
those genes(example RED
FLOWER) is called the
PHENOTYPE.
PHENOTYPES
• To determine the
outcome of a cross, you
can use a punnett
square.
EXAMPLE:
A homozygous
dominant red flower
crosses with a
homozygous recessive
flower, what are the
genotype and
phenotype of the
offspring?
R
R
r
Rr
Rr
r
Rr
Rr
•
RR x rr
•
•
GENOTYPE: 4 Rr
PHENOTYPE:4 red flowers
• B=black, b=white
• REMEMBER: the
dominant letter
always goes first!!!!
• EXAMPLE: 2
heterozygous black
bunny crosses with
one another. What
are the genotype and
phenotype of the
offspring?
•
Bb x Bb
Genotype=1BB,2Bb,1bb
Phenotype=3 black and 1
white
B
b
B
BB
Bb
b
Bb
bb
INCOMPLETE DOMINANCE
Sometimes,
there are two
dominant
alleles and no
recessive
alleles.
Ex: flower color
In some flowers, red
and white are both
dominant.
A red flower has the
phenotype ______ and
the
genotype RR.
A white flower has the
phenotype ______ and
the genotype
What if you cross a RED (RR)
flower with a WHITE (WW)
flower?
R
R
W
RW
RW
W
RW
RW
What color are the offspring?
R
R
W
RW
RW
W
RW
RW
WHIT
E +
RED
PINK
So, when a trait is inherited by
incomplete dominance, there
3
are ____
possible phenotypes
Red
White
Pink
3 possible genotypes.
and ____
RR
WW
RW
Multiple Alleles
In some cases, there are more than 2
possibilities.
Ex: hair color, eye color, skin color
Blood Type
• 2 Dominant alleles – A and B
Genotype
• 1 recessive allele – O
AA
AO
AB
BB
BO
OO
Phenotyp
e
A
A
AB
B
B
O
What if you cross a AO parent
with a BO parent?
A
O
B
AB
BO
O
AO
OO