BIOLOGY 111
CHAPTER 11: The First Geneticist:
Mendel and His Discoveries
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The First Geneticist:
Mendel and His Discoveries
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11.1 Mendel and the Black Box
11.2 The Experimental Subjects: Pisum sativum
11.3 Starting the Experiments: Yellow and Green Peas
11.4 Another Generation
11.5 Crosses Involving Two Characters
11.6 Reception of Mendel's Ideas
11.7 Incomplete Dominance and Co-dominance
Mendel and His Discoveries:
Gregor Mendel (1822 –1884)
Austrian monk famous for his breeding
experiments between1856 and 1863
Known as the father of modern genetics, but
he had no knowledge of ____, ___________,
______ or _______.
Mendel and His Discoveries:
Gregor Mendel (1822 –1884)
Austrian monk famous for his breeding
experiments between1856 and 1863
Known as the father of modern genetics, but
he had no knowledge of DNA, Chromosomes,
______ or _______.
Mendel and His Discoveries:
Gregor Mendel (1822 –1884)
Austrian monk famous for his breeding
experiments between1856 and 1863
Known as the father of modern genetics, but
he had no knowledge of DNA, Chromosomes,
Mitosis or Meiosis.
Mendel demonstrated that the inheritance of
certain ____ follow particular _______
Mendel and His Discoveries:
Gregor Mendel (1822 –1884)
Austrian monk famous for his breeding
experiments between1856 and 1863
Known as the father of modern genetics, but
he had no knowledge of DNA, Chromosomes,
Mitosis or Meiosis.
Mendel demonstrated that the inheritance of
certain traits follow particular patterns
Mendel and His Discoveries:
How could Mendel accomplish this?
He applied the
to his
observations regarding a common pea plant,
Pisum sativum
Mendel and His Discoveries:
How could Mendel accomplish this?
He applied the Scientific Method to his
observations regarding a common pea plant,
Pisum sativum
Mendel was able to answer questions about
inheritance by carefully observing _______
____ and the resulting traits of their _______.
Mendel and His Discoveries:
How could Mendel accomplish this?
He applied the Scientific Method to his
observations regarding a common pea plant,
Pisum sativum
Mendel was able to answer questions about
inheritance by carefully observing parental
traits and the resulting traits of their _______.
Mendel and His Discoveries:
How could Mendel accomplish this?
He applied the Scientific Method to his
observations regarding a common pea plant,
Pisum sativum
Mendel was able to answer questions about
inheritance by carefully observing parental
traits and the resulting traits of their offspring.
Mendel’s Conclusions:
1.
Parents passed inheritable elements to offspring
2.
Each parent passes their own copy of inheritable
elements to their offspring (they were in pairs)
3.
Some inheritable traits were connected and were
usually passed together.
4.
The paired inheritable elements generally had a
25% (1 out of 4) chance of being passed to
offspring
The First Geneticist:
Mendel and His Discoveries
•
•
•
•
•
•
•
11.1 Mendel and the Black Box
11.2 The Experimental Subjects: Pisum sativum
11.3 Starting the Experiments: Yellow and Green Peas
11.4 Another Generation
11.5 Crosses Involving Two Characters
11.6 Reception of Mendel's Ideas
11.7 Incomplete Dominance and Codominance
Mendel’s Experiments:
Life Cycle of the Pea Plant
1.
Self Pollination: Pollen from male
Anthers fall on female Stigma
2.
Fertilization: Pollen fertilizes eggs
in ovary (pod) and become seeds.
3.
Germination: Seeds grow into a
new plant (seedling)
4.
Development: Seedlings mature
and produce offspring.
Mendel’s Experiments:
Tracking Traits:
Mendel identified various traits that he
wanted to track.
Mendel’s Experiments:
Tracking Traits: Terminology
Mendel observed the following during cross
pollination experiments:
Plants that always expressed a specific trait were
called True Breeding plants.
We now know that they must have been
homozygous, meaning that because both
alleles were the same (YY or yy), they could
only pass one type
Mendel’s Experiments:
Cross Pollination Experiments:
Cross Pollination: The ability of a
plant to fertilize a different plant by
passing pollen (sperm) to eggs.
Mendel realized he could accomplish
this (like a bee) using a paint brush.
He initially worked with plants that
had either Green or Yellow seeds
(peas)
Mendel’s Experiments:
Cross Pollination:
Mendel took pollen from a true
breeding GREEN seed plant and
passed it to a true breeding YELLOW
seed plant.
When this was done, the offspring
always had YELLOW seeds!
A
B
A
Mendel’s Experiments: (single cross)
What did Mendel learn from these single
crosses?
Mixed genotypes did not produce mixed
(blended) phenotypes.
The traits were ‘hidden’ as recessive alleles, so
all Mendel saw were yellow seeds…
But Mendel did not see any green seeds until he let the
heterozygous offspring self-fertilize and reproduce
The First Geneticist:
Mendel and His Discoveries
•
•
•
•
•
•
•
11.1 Mendel and the Black Box
11.2 The Experimental Subjects: Pisum sativum
11.3 Starting the Experiments: Yellow and Green Peas
11.4 Another Generation
11.5 Crosses Involving Two Characters
11.6 Reception of Mendel's Ideas
11.7 Incomplete Dominance and Codominance
Mendel’s Experiments: (single cross)
Crossing Traits : Terminology
Mendel found that there were no green seeds in
the F1 first generation.
So… Mendel let the F1 generation self-fertilize and
reproduce to observer the types of offspring.
Mendel’s Experiments: (single cross)
Crossing Traits : Terminology
Mendel found that there were no green seeds in
the F1 first generation.
But green seeds appeared in a second F2
generation!
This is because the (F1) generation was not
true breeding, they were heterozygous
Mendel’s Experiments: (single cross)
Crossing Traits : first generation
True Breeding plants could only pass either Green or
Yellow (YY or yy)
Both parents were true breeding, so all offspring were
heterozygous!
Mendel’s Experiments: (single cross)
Crossing Traits : first generation
Heterozygous plants produced different offspring than
their true-breeding (homozygous) parents
Now, there were 4 different combinations, and 1 of the 4 (25%)
were green (yy)!
The First Geneticist:
Mendel and His Discoveries
•
•
•
•
•
•
•
11.1 Mendel and the Black Box
11.2 The Experimental Subjects: Pisum sativum
11.3 Starting the Experiments: Yellow and Green Peas
11.4 Another Generation
11.5 Crosses Involving Two Characters
11.6 Reception of Mendel's Ideas
11.7 Incomplete Dominance and Codominance
Incomplete Dominance and Codominance
Mendel’s discoveries also had some variation.
Sometimes, a heterozygote (Xx) phenotype would
be intermediate between the two alleles. This is
called Incomplete Dominance.
Incomplete Dominance and Codominance
Mendel’s discoveries also had some variation.
Sometimes both alleles are expressed
independently – each having it’s own specific
characteristic. This is called Codominance.
An example is how human blood types are
expressed.