Transcript 11.1 the work of gregor mendel

11.1
THE WORK OF GREGOR
MENDEL
(THE PEA MONK)
1. Every living thing- plant or
animal, microbe, or human
being – has a set of
characteristics inherited
from its parents or parent.
Heredity holds the key to what
makes each species unique.
The scientific study of heredity is
genetics.
Gregor Mendel, an
Austrian monk, had a very
great life studying math
and science, teaching high
school, and piddling in the
monastery gardens.
2.
This man was fascinated with
ordinary garden peas. He
could never ever be bored
because these things are the
source of a great deal of
knowledge 
3. Pea flowers
produce pollen,
which contains the
male plants’
reproductive cells
or sperm
(stamen).
The flowers also
have female parts,
which produce egg
Cells (carpel).
# 4 & 5 make up the male parts = pollen
#2 & 3 make up the female part.
4. During sexual reproduction,
the male and female cells join,
a process called fertilization.
Fertilization produces a new cell,
which develops into a tiny
embryo encased within a seed.
5.
Pea flowers are normally selfpollinating, which means that
sperm cells in pollen fertilize the
egg cells in the same flower.
The seeds that are produced inherit
all of their characteristics from the
single plant that bore them. They
have a single parent!
6. Mendel discovered that his pea
plants were true-breeding,
meaning that if they were allowed
to self-pollinate, they would
produce offspring identical to
themselves!!
One stock of seeds would produce
only tall plants, another short
ones. One line produced green
seeds, another yellow ones.
7. Mendel wanted to produce seeds
by joining sperm and eggs from
two different plants. To do this
he had to prevent selfpollination!!!
This is what he did! He cut away
the pollen-bearing male parts
then dusted pollen from
another plant onto the flower.
7. This process is called crosspollination.
It produced seeds that had two
different plants as parents!
This made it possible for Mendel to
cross-breed plants with different
characteristics, and then study the
fascinating results!!
8.
Mendel studied seven different
pea plant traits.
A trait is a specific characteristic
that varies from one individual
to another.
Each of the 7 traits Mendel studied
had two contrasting characters,
such as green/yellow seeds color,
tall/short plants, etc.
9. Mendel crossed plants with
contrasting characters and studied
their offspring.
He called the original set of
parents the P (parental)
generation. He called the
offspring the F1 “first filial”
generation.
The offspring of crosses between
parents of diff traits are called
hybrids.
Hybrids from a cross
between a tall plant and a
short plant
10. Mendel was a busy man! He was
also surprised! All of the offspring
in the F1 generation had the
character of ONLY one of the
parents!
The character of the other parent
seemed to have
disappeared!!...Was this magic?
Or was there another explanation?
Hybrids from a cross
between a tall plant and a
short plant
11. Mendel drew two conclusions:
1. Biological inheritance is determined
by factors that are passed from one
generation to the next.
(Today, we call the chemical factors that
determine traits genes. Each of the
traits Mendel studied was controlled by
one gene that occurred in two
contrasting forms.)
11. (These contrasting forms
produced the different characters
of each trait. The diff forms of a
gene are called alleles).
X
= Purple
X
= Axial
X
X
X
X
X
= Yellow
2. The Principle of
dominance states that some
alleles are dominant &
others are recessive.
An organism with the
dominant form of an allele
will always exhibit that form of
the trait.
2. An organism with the
recessive allele for a
particular form of a trait will
exhibit that form ONLY when
the dominant allele for that
trait is NOT present!!
12. Mendel wanted to know if
the recessive alleles had
disappeared, or were they
still present in the F1 plants??
He allowed all seven kinds of
F1 hybrid plants to produce an
F2 (2nd filial) generation by
self-pollination.
13. The results of the F1 cross were
REMARKABLE!!
When Mendel compared the F2
plants, he discovered that the
traits controlled by the recessive
alleles had reappeared!!
Roughly ¼ of the F2 plants showed
the trait controlled by the
recessive allele!!!
P Generation
F1 Generation
F2 Generation
Recessive allele traits
reappeared in about ¼ of
the F2 plants
14. WHY did the recessive alleles
seem to disappear in one
generation and reappear in the
next???
The answer is segregation!!!
The reappearance of the recessive
trait (short plant in this case)
indicated that it had somehow
become separated from the
allele for tallness.
So how did this separation or
segregation occur? Mendel
suggested that the alleles for
tallness and shortness in the F1
plants segregated from each
other during the formation of the
sex cells, or gametes.
15. If F1 plants inherit an allele for
tallness from one parent and an
allele for shortness from another
parent, all the F1 plants are tall
because the allele for tallness is
dominant.
When each F1 plant flowers and
produces gametes, the two alleles
segregate from each other so
that each gamete carries only a
single copy of each gene.
Therefore, each F1 plant produces
two types of gametes ---those with
the allele for tallness and those
with the allele for shortness.
Figure 11-5 from pg. 266
Draw and Label
Gamete formation:
alleles