Download Mendel`s Excellent Experiments

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Can 2 dwarfs have a tall child?
Why are more boys color blind than girls?
Does having blonde hair mean getting blue
eyes too?
If someone is bald what’s the chance their
children will go bald too?
If a couple has 5 girls, what’s the chance the
next child will be a boy?
Inquiring Minds Want to KNOW!!
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Mendel’s experiments showed that the
inheritance of traits is predictable
Gregor Mendel was an Austrian monk who
wore many hats –
 Chief monk
 High school science teacher
 Monastery’s vegetable gardener

While working in his garden, Mendel noted
that the pea plants had a 7 traits that only
came in two forms
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Mendel’s purpose in carrying out 1000’s
of experiments on pea plants to study
the process of heredity – the passing
down of traits from parents to offspring.
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Pea plants reproduce sexually which involves
??? Parents
Flowers contain both male and female
reproductive organs
Stamen – Male
Pistil – Female
Makes Pollen/Sperm
Makes Eggs

Mendel developed a method to crosspollinate or “cross” two plants with
different forms of the same trait.
He started with purebred plants.
Purebred plants produce plants that look
identical to the parent plant.
 He called the Parent generation the “P
generation” for short.
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When Mendel crossed
pure-bred tall plants with
purebred short plants. ..

All of offspring were Tall!

100% Tall : 0% Short
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The offspring generation are called “F
generations.”

The “F” stands for filial –Latin for “child”
Each successive generation of offspring are
noted by a little number after the letter “F”
(F1).
 The second generation (from mating the F1’s
together) form the F2 generation.
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When the plants in the F1 generation were
full grown, Mendel allowed them to selfpollinate which formed seeds he then
planted.
 The F2 generation plants that grew from
the seeds were, surprisingly, a mix of tall
and short plants!
 The shortness trait had reappeared after
skipping a generation!
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Approx. 3/4 (75% ) were tall
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The remaining 1/4 (25% ) of the plants
were short.
• Mendel observed patterns in the first and second
generations of his crosses.
6.3 Mendel and Heredity
• Mendel observed patterns in the first and second
generations of his crosses.
Mendel reached several conclusions on
the basis of his experimental results.
 Heredity is predictable and not caused by
chance alone.
 Heredity
is controlled by 3 principles
1. Law of Segregation
 Organisms inherit one of each gene, from
each parent
 During sex cell formation, the 2 genes get
separated into different sex cells
 Today we know that what Mendel
hypothesized actually occurs when
chromosomes separate in anaphase I and 2 of
meiosis.
2. Dominant gene forms can “mask” or
“hide” the expression of recessive forms of
the same gene.
3. Law of Independent Assortment
• Each trait is controlled by separate genes
which are passed from parents to offspring
independently of one another.
• Ex. Just because a person inherits red hair
doesn’t automatically mean they’ll have freckles
too.
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Though his work was unrecognized during his
lifetime, today he’s known as
”The Father of Genetics” for developing the
Laws of Inheritance
Genetics is the scientific study of heredity - the
process of passing down genetic information
Mendel’s experiments showed that the
inheritance of traits from parents to
offspring was _____________________.
 Why is this finding so important – what
are its implications?
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When you have two genes that are
different (not purebred) then you are
called a Hybrid!
› Name another thing you think about when
you hear the word “Hybrid.” What does it
mean in your example?
Geneticists use letters to represent alleles.
 A Dominant allele is ALWAYS represented
with a capital letter!

› Tall plants = T

A recessive allele is ALWAYS represented by
a lowercase version of THE SAME LETTER OF
THE DOMINANT ALLELE!
› Short plants = t

This way, you always know that the “T’s” go
together!
When a plant inherits two Dominant
alleles for tall stems, its alleles are written
as TT.
 When a plant inherits two recessive
alleles for short stems, its alleles are
written as tt.
 When a plant inherits one allele for tall
stems and one allele for short stems, its
alleles are written as Tt.

An organism’s traits are controlled by the
alleles it inherits from its parents.
 Some alleles are Dominant, while other
alleles are recessive.
 A Dominant allele is one whose trait is
ALWAYS “expressed “ or seen
 A Recessive allele is “masked” or hidden
by a dominant trait. It is only expressed
when no dominant allele is inherited too.

Unfortunately, the importance of
Mendel’s discovery was not recognized
during his lifetime.
 Then, in 1900, three different scientists
rediscovered Mendel’s work.
 These scientists quickly recognized the
importance of Mendel’s ideas.
 Because of his work, Mendel is often
called the Father of Genetics.

Today, we use the word “Gene” instead
of “factor.”
 Alleles are the different forms of the same
Gene.
 Gene – Determines trait ex.Plant height
 Alleles – Determine the FORM of the trait
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ex. Tall or Short
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