Transcript Mendel`s Peas

Mendel and Genetics
A little history:
Prior to 1820s, people knew
about inherited traits and
used this concept to raise
plants and animals: fast
horses would breed fast
horses.
As far a people, the generally accepted theory was that
children were a blend (or combination) of characteristics
of both the mother and father: A blonde woman and a
dark-haired man would have a baby with brown hair (a mix
of blonde and dark hair).
Mendel and Genetics
In the early 1800s, a monk
by the name of Gregor
Mendel changed
everything we know about
Genetics.
Mendel bred and studied
pea plants.
He noticed that the pea
plants had specific traits
(characteristics) that were
passed on from generation
to generation.
Mendel’s Peas – Traits he Studied
These traits are physical features of the pea plants: they
would produce one or the other feature (white or purple
flowers).
What would offspring look like if Mendel
bred a yellow and green pea ?
• First, these plants breed “true”. A plant
producing yellow peas will always produce
yellow peas.
• If traits were blended, a plant with yellow
peas bred to a plant with green peas
would produce yellow-green peas.
What Mendel Observed
Seed Color – Breeding a
yellow pea and a green pea
X
Key: P1 = one parent
P2 = the other parent
F1 = first generation offspring
F2 = second generation offspring
This observation was consistent with all traits Mendel observed.
Important Questions
• If the offspring were a blend of the
parents, what color would the F1 offspring
be?
• Does one color “disappear” in the F1
offspring? Which color?
• Does that color “reappear” in the F2
generation?
What Mendel Observed
• When a plant producing green peas was
crossed with a plant producing yellow peas, all
the offspring produced yellow peas:
X
• In that first generation, not a single plant
produced green peas.
• When the yellow pea plants were bred to each
other, the green peas returned!
X
Mendel's work showed:
•Each parent contributes one factor of each
trait to the offspring.
•The blending theory of inheritance was
discounted. Traits are not mixed or combined.
•Males and females contribute equally to the
traits in their offspring.
•Acquired traits are not inherited.
Mendel’s Laws
• Law of Segregation:
each gamete (sex
cell) only receives
one copy.
translation
• Law of Independent
Assortment: separate
genes for separate
translation
traits are passed
independently of one
another from parents
to offspring
You get one set
of traits from
your mother and
the same set of
traits from your
father.
Traits will not
affect each other.
If one parent is
weaker, their trait
will not be affected
by the stronger
parent.
Vocabulary
• Trait
• Alleles
• Genotype - the genetic make-up of a trait in an organism
• Phenotype - the physical appearance of the trait in an
organism
• Heterozygous
• Homozygous