Transcript Gregor Mendel and His Peas - Monroe Township School

A true story about an Austrian monk and how he
became THE FATHER OF GENETICS
Once upon a time…
There was an Austrian monk
named Gregor Mendel.
He was young, about 21, when
he was tasked with tending
the monastery’s garden.
Peas, Peas,
look at all
the pretty
peas
Now Gregor noticed some interesting things….
He observed how they grow, and
how some peas looked very
similar to each other while
some looked completely
different!
Great Scott!
Look at all
these different
peas!
Gregor observed 7 different kinds
of pea plants….
Each time the peas had contrasting traits.
There was….
 Tall plants and short plants (long or short stems)
 Green pods and yellow pods
 Inflated pods or constricted pods
 Smooth seeds or wrinkled seeds
 Green seeds and yellow seeds
 Axial flowers and terminal flowers
 And finally, pretty purple flowers and pretty white
flowers
But Gregor wanted to know more…
So Gregor, went to the University of Vienna to learn
more. He studied science and statistics. Then FINALLY
he got to return to his precious peas.
So Gregor got to work!
Gregor worked his little scientist hands to the bone! He
collected seeds from all his pea plants and recorded
what characteristics the parent plant had.
He carefully made sure to control what
pollen went where
 Pollination- pollen is transferred
to the stigma
 Anthers- where pollen is produced
(male)
 Stigma- female reproductive part
of a flower
 Self-Pollination- pollen lands on
the stigma of the same plant
 Cross Pollination- pollen comes
from a different plant
He sometimes put pollen on the stigma
of the same plant
 Self-pollination- Pollen and stigma from the same
plant
Or sometimes… he chose to use pollen from
a different plant
 Cross pollination- Pollen and stigma from different
plants
He discovered what we call the
Law of Segregation
 A pair of alleles is segregated
(separated) during the formation
of gametes
 Remember! Genes occur in pairs!

One from the mother and one
from the father
mother
father
Then he planted his beautiful seeds!
He noticed that purple flowering plants came from the
seeds from purple flowering plants, but to his surprise
he saw that white flowering plants also sometimes
came from purple flowering plants! How could that
be!
What he’ll soon
find is the Law of
Dominance!
First he tried crossing 2 pure
contrasting traits (P-Generation)
P
g
G
G
G g
G g
F1
g
Gg
Gg
GG x gg
Key:
G=green
g= yellow
Phenotype:
100% green
Genotype:
100% heterozygous
Then he tried crossing the F1 generations
and the yellow peas returned!
F1
G
G
g
G G
G g
F2
g
Gg
g g
Some genes must be
dominant to other genes!
Gg x Gg
Key:
G=green
g= yellow
Phenotype: 3:1
75% green
25% yellow
Genotype: 1:2:1
25% homozygous GG
50% heterozygous
25% homozygous gg
He discovered the Law of Dominance
 Is the plant homozygous or
heterozygous ?
 Perform a test cross!
 Crossing the genotype in
question with a
homozygous recessive
Test Cross
Practice! GG or Gg?
? x gg
P
Key:
G=green
g= yellow
g
G g
G g
F1
g
Gg
Phenotype:
100% green
Gg
Genotype:
100% heterozygous
Practice! GG or Gg?
P
? x gg
Key:
G=green
g= yellow
F1
Phenotype:
50% green
50% yellow
Genotype:
And always remember….
Give PEAS a Chance!