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Gregor Mendel and His PeasA 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 podsInflated pods or constricted podsSmooth seeds or wrinkled seedsGreen seeds and yellow seedsAxial 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 wherePollination- pollen is
transferred to the stigma Anthers- where pollen is
produced (male) Stigma- female reproductive
part of a flowerSelf-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 plantSelf-pollination- Pollen and stigma from the
same plant
Or sometimes… he chose to use pollen from a different plantCross pollination- Pollen and stigma from
different plants
He discovered what we call the Law of SegregationA pair of alleles is
segregated (separated) during the formation of gametesRemember! 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)
G G
g
g
G G
G G
g g
g g
Key: G=greeng= yellow
GG x ggP
F1 Phenotype:
100% green
Genotype:100% heterozygous
Then he tried crossing the F1 generations and the yellow peas returned!
G
G
g
g
G G
G
G
g
g
g g
F1 Key:
G=greeng= yellow
Gg x Gg
Phenotype: 3:175% green25% yellow
Genotype: 1:2:1 25% homozygous GG50% heterozygous25% homozygous gg
F2
Some genes must be dominant to other genes!
He discovered the Law of DominanceIs the plant
homozygous or heterozygous ?
Perform a test cross!
Crossing the genotype in question with a homozygous recessive
Test Cross
Practice! GG or Gg?
g
g
G G
G G
g g
g g
P
F1
Key: G=greeng= yellow
Phenotype:100% green
Genotype:100% heterozygous
? x gg
Practice! GG or Gg?? x ggP
F1
Key: G=greeng= yellow
Phenotype:50% green50% yellow
Genotype:
And always remember….Give PEAS a Chance!