Download 7th Grade Science

Gregor Mendel
(1822-1884)
The Father of
Genetics
Pg 77
Why is Mendel’s work
important?
© Fall 2005, Pflugerville ISD, 7th Grade
copyright cmassengale
1
Gregor Johann Mendel
Austrian monk
Studied the
inheritance of traits in
pea plants
Developed the laws of
inheritance
Mendel's work was
not recognized until
the turn of the 20th
century
© Fall 2005, Pflugerville ISD, 7th Grade
2
Gregor Johann Mendel
Between 1856 and
1863, Mendel
cultivated and tested
thousands of pea plants
He found that the
plants' offspring
retained traits of the
parents
© Fall 2005, Pflugerville ISD, 7th Grade
copyright cmassengale
3
Particulate Inheritance
Mendel stated that
physical traits are
inherited as “particles”
Mendel did not know
that the “particles” were
actually Chromosomes &
DNA
copyright cmassengale
© Fall 2005, Pflugerville ISD, 7th Grade
4
Why peas, Pisum sativum?
Can be grown in a
small area
Produce lots of
offspring
Produce pure plants
when allowed to selfpollinate several
generations
Can be artificially
cross-pollinated
© Fall 2005, Pflugerville ISD, 7th Grade
copyright cmassengale
5
Mendel and His Peas
• Mendel tested 7 traits:
1.
2.
3.
4.
5.
6.
7.
Flower color
Flower position
Seed color
Seed shape
Pod shape
Pod color
Plant height
http://www.fieldmuseum.org/exhibits/traveling_mendel.htm
© Fall 2005, Pflugerville ISD, 7th Grade
Mendel and His Peas
• Mendel crossed flowers that were truebreeding for each characteristic.
• He crossed a purple (PP) flowered plant
with a white (pp) flowered plant.
(Parent Generation)
http://biology.kenyon.edu/courses/biol114/KH_lecture_images/Mendel/Mendel.html
© Fall 2005, Pflugerville ISD, 7th Grade
Mendel and His Peas
• Where did the
white color go??
© Fall 2005, Pflugerville ISD, 7th Grade
White Parent
• The first
generation (F1) of
plants all had
purple flowers.
(pp)
Purple Parent (PP)
(Pp)
(Pp)
(Pp)
(Pp)
Mendel and His Peas
• In the second
generation (F2) he had
3 purple flowered
plants, and 1 white
flowered plant.
© Fall 2005, Pflugerville ISD, 7th Grade
Purple Parent (Pp)
Purple Parent (Pp)
• Mendel took two of his
first generation (F1 x F1)
purple flowered plants
and crossed them
together.
(PP)
(Pp)
(Pp)
(pp)
Mendel and His Peas
• Mendel noticed in the first generation, all
of the white flowers seemed to
disappear.
• He called this a recessive trait.
• The white color faded into the
background at first.
• It showed up in the next generation
when he pollinated the flowers.
© Fall 2005, Pflugerville ISD, 7th Grade
Mendel and His Peas
• The color (purple) that seemed to mask
over the recessive color was named the
dominant trait.
© Fall 2005, Pflugerville ISD, 7th Grade
Mendel and His Peas
• Mendel was responsible for figuring out
that each plant carried two sets of
instructions for each characteristic (one
from the “mom” and one from the
“dad”).
• Like many scientists, his work was not
accepted until after his death.
© Fall 2005, Pflugerville ISD, 7th Grade
Let’s Review
1. If you crossed a true-breeding black
rabbit with a true-breeding white
rabbit, all of the offspring would be
black. Which trait is dominant in
rabbits: black fur or white fur?
2. Which trait is recessive?
© Fall 2005, Pflugerville ISD, 7th Grade
Answer
White Rabbit (bb)
• The trait for black
fur is dominant
over the trait for
white fur. The
white fur trait is
recessive.
Black Rabbit (BB)
(Bb)
(Bb)
(Bb)
(Bb)
http://www.buckeyevalleyfarms.freeservers.com/photo.html
© Fall 2005, Pflugerville ISD, 7th Grade
Science Humor
© Fall 2005, Pflugerville ISD, 7th Grade
Mendel and His Peas
Vocabulary
1. Heredity- the passing of traits from
parent to offspring.
2. Self-pollinate- A plant is often able to
pollinate by itself because it contains
both the male and female reproductive
structures. This only requires 1 parent.
© Fall 2005, Pflugerville ISD, 7th Grade
Mendel and His Peas
3. True-breeding- all of the offspring will
have the same trait as the parent when
self-pollinated
4. First-generation- the very first set of
offspring from two parents
5. Dominant trait- the trait observed when
at least one dominant allele for a
characteristic is inherited
© Fall 2005, Pflugerville ISD, 7th Grade
Mendel and His Peas
6. Recessive trait- a trait that is apparent
only when two recessive alleles for the
same characteristic are inherited
7. Genes- a segment of DNA that carries
hereditary instructions and is passed
from parent to offspring
8. Alleles- multiple forms of the same
gene
© Fall 2005, Pflugerville ISD, 7th Grade
Mendel and His Peas
9. Genotype- an organisms inherited
combination of alleles
10. Phenotype- an organisms inherited
appearance
© Fall 2005, Pflugerville ISD, 7th Grade