Transcript The Monk who loved peas

The Monk who loved peas
How to Make a Living Thing
Gregor Mendel
 Monk, failed teacher, pea-lover, genetic genius
 From growing peas, Mendel noticed that
offspring did not always have the same traits as
the parents
But then the parent’s trait would show up again in a
“grandchild,” or 2nd generation
 So Mendel began to experiment, attempting to
grow peas with certain traits, or characteristics
The Proof is in the Peas

Peas were an excellent
choice for his research
for two reasons
They can self-pollinate,
creating offspring with the
same traits as the parent
Or, they can crosspollinate with other peas
The Experiment
Mendel looked at one
characteristic at a time
(color, height, shape)
 If a pea plant has a white
flower, then it selfpollinates, you’ll have
offspring with white
flowers
 What happens if a
purple-flowered pea
plant cross-pollinates a
white-flowered pea
plant?

Mendel’s Discovery

Mendel noticed the
offspring of a purpleflowered pea plant and a
white one was always
purple
BUT, the “grandchildren”
or 2nd generation, would
have 1 white-flowered
pea plant for every three
purple ones
Dominant Traits

Dominant traits are the
ones always showing up
in the first generation
The purple-flowered pea
plant

In a Punnett Square,
dominant traits are
symbolized by a capital
letter
Recessive Traits

“Fade into the back”
The white-flowered pea
plant
These traits reappear in
the 2nd generation
 MUST be paired with
another recessive allele

R
r
R
RR
Rr
r
Rr
rr
Incomplete Dominance
Sometimes, one trait is
NOT dominant over the
other
 Each allele provides
some influence
 Hair texture—curly,
straight, and wavy—is an
example in humans

Genes
The instructions for one
particular trait are called
a gene
 You have 2 forms of the
same gene for every
characteristic

1 from Mom, 1 from Dad

Hair color, eye color,
height, hitchhiker’s
thumb, etc.
Alleles

The form of a trait given
by one parent

So, for each gene, you
have 2 alleles

Either dominant (capital
letter) or recessive
(lower-case)
Genotype and Phenotype
·Both inherited traits form a
genotype
--Aa; rr; etc.
·The appearance of a
characteristic is the
organism’s phenotype
--a purple flower;
wrinkled peas; wavy hair
Genetic Probability and Pedigrees



Probability is the
mathematical chance of an
outcome
Aa x Aa has a 25% chance of
getting aa as an outcome;
25% AA; 50% Aa
Pedigrees are like family
trees for determining the
probability of genetic
diseases like cystic fibrosis