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!