Download different forms of a gene

Mendel and His Pea Plants
Bell Question:
What is the
difference between
inherited and noninherited traits?
Answer:
Inherited traits are passed from parents to offspring through
DNA. Non-inherited traits are learned behaviors or things
that happen to you.
Mendel and His Pea Plants
Gregor Mendel
• Austrian
• Recommended to enter an abbey
by his physics teacher
• Becoming a friar allowed
Mendel to continue his studies in
various science fields without
having to pay for it
• Mendel was interested in
astronomy, physics, meteorology,
beekeeping, and selective breeding
Mendel and His Pea Plants
What is selective breeding?
Selective breeding is agriculture! It is breeding plants or
animals for specific traits.
• pest resistant corn
• stronger oxen
• sheep with thicker wool
Can you think of others?
People have been doing selective breeding for thousands of
years.
Mendel and His Pea Plants
wild wheat
wheat we eat
wild corn
Mendel and His Pea Plants
Mendel started his selective
breeding experiments with mice.
However, the head of the abbey
was not happy about using and
breeding animals.
So Mendel switched to pea plants.
Mendel and His Pea Plants
It was a great decision! Pea plants
are glorious little plants!
• Reproduce quickly
• Have easily observed traits
• Have DISTINCT traits – The traits are “this” OR “this.” There are no
ranges.
For example, peas are either green or yellow … not green,
yellow, yellowish-green, greenish-yellow, or even chartreuse.
Mendel and His Pea Plants
Another great reason to use pea plants is you can control
which plants are reproduced.
pollen (sperm cells)
pistil
For plants to reproduce,
pollen needs to get to a
plant’s pistil.
Plants can do this
themselves. This is selfpollination.
Or you can take pollen from
one plant and put it on the
pistil of another. This is
called cross-pollination.
Mendel and His Pea Plants
Mendel started with true-breeding
plants
• Offspring are the same as the
parent
• What you start with is what you
get
True-breeding plants self-pollinate
Mendel and His Pea Plants
Word
Definition
a plant that
Trueproduces
breeding offspring with
traits that are
like the parents
Picture
Mendel and His Pea Plants
Mendel allowed some plants to
self-pollinate.
Some plants he cross-pollinated.
Why did Mendel cross-pollinate?
Cross-pollination introduces
VARIATION!
Mendel and His Pea Plants
Word
Definition
when the
pollen of one
Crossplant reaches
pollination the pistil of a
flower on a
different plant
Picture
Mendel and His Pea Plants
In daughter generations (the offspring), Mendel was
collecting data for what things LOOKED like.
What something looks like is the phenotype.
Mendel and His Pea Plants
Word
Definition
how a trait
appears or is
Phenotype
expressed
(what it looks
like)
Picture
blue flower
Mendel and His Pea Plants
But what makes something look a certain way? What gave
Mendel yellow peas or white flowers? Genotypes!
We inherit two sets of chromosomes – one from each parent.
On each chromosome, there are genes that code for
phenotypes.
You inherit one gene from your mother and one gene from
your father. These different forms of the genes are called
alleles.
The combination of these alleles is your genotype.
Mendel and His Pea Plants
Word
Definition
Gene
section of a
chromosome
that has
genetic
information for
one trait
Picture
Mendel and His Pea Plants
Word
Definition
Picture
blue flower
Allele
different forms
of a gene
brown
flower
Mendel and His Pea Plants
Word
Definition
the two alleles
that control the
Genotype
phenotype of a
trait
Picture
Gg for green
peas
Mendel and His Pea Plants
For certain phenotypes – like those
measured by Mendel in the pea
plants – you only need those two
alleles to code for what something
looks like.
Those two alleles make the genotype
for that specific phenotype.
Let’s look at what Mendel
did with his true-breeding
plants when he looked at
pea color…
Mendel and His Pea Plants
Mendel bred a true-breeding pea plant that produced green peas with a
true-breeding pea plant that produced yellow peas. Then he bred two
pea plants to create a 2nd generation.
+
2nd generation
+
Wait! What?!?
Mendel and His Pea Plants
• To figure why this happened
with the phenotypes, we need
to look at the plants’ genotypes.
• In pea plants, green peas are
the dominant genotype. This
means that it is also the more
common phenotype seen.
• A dominant genotype means that will be the genotype that
“wins.” This is the trait that is expressed in the phenotype.
• If either pea plant gives its offspring a green pea gene (the
dominant one), then the peas will be green.
Mendel and His Pea Plants
Word
Definition
allele that
Dominant blocks another
allele and is
trait
expressed in
the phenotype
Picture
green pea color is
dominant to yellow
Mendel and His Pea Plants
That makes the yellow pea color recessive.
Recessive genes are more rare, and they create less
frequently seen phenotypes.
For something to show a recessive phenotype, it
needs two of the recessive genes. Why?
Because if it had one recessive gene and one
dominant gene, the dominant gene would be
expressed in the phenotype.
Mendel and His Pea Plants
Word
Recessive
trait
Definition
Picture
allele that is
blocked by
another allele
yellow peas are
recessive
Mendel and His Pea Plants
Let’s look at the genotypes of the pea colors.
This is a Punnett Square. It allows us to easily see ratios of
offspring for simple genotypes.
Mendel and His Pea Plants
Word
Definition
Punnett
Square
model used to
predict
probable ratios
of genotypes
and
phenotypes of
offspring
Picture
Mendel and His Pea Plants
You place the genotypes of each parent on the top and the left sides of
the square.
Let’s start with the true-breeding plants from our example: one plant
that only produces green peas and another that produces only yellow
peas.
G
G
We are looking at green vs.
yellow. Since green is
dominant, we will use a “G”
for green and “g” for yellow.
Always use capital letters for
the dominant allele.
Mendel and His Pea Plants
We know the genotype of the plants that produce yellow
peas. Yellow peas are a recessive genotype. So the two
gg
alleles would be _______.
Remember, we use the code
based on the dominant
genotype, so lowercase “g”
g
g
means yellow. If the genotype
were Gg, what color would
G
the peas be?
green, because there is a
dominant allele (G)
G
Mendel and His Pea Plants
Now, we separate the alleles. Remember, we get one set of
genes from our father and one from our mother.
Let’s distribute! Do it
the same way every
time so it becomes a
habit.
g
g
G
G
G
G
G
G
Mendel and His Pea Plants
Now, the other set of genes. Dominant alleles are always
listed first.
g
g
G
Gg
Gg
G
Gg
Gg
Mendel and His Pea Plants
These are the genotypes from the first daughter generation.
What are the phenotypes?
g
Gg
G
G
green
pea
Gg
green
pea
g
Gg
green
pea
Gg
green
pea
What is the frequency of
the genotypes?
Gg appears 4 out of 4
times, or 100%.
Mendel and His Pea Plants
What if we take two daughter plants from the first
generation and cross them?
• What are the genotypes for the mother and father
plants? Gg
• What are the phenotypes for the peas? green
• What do you think will happen?
Mendel and His Pea Plants
Fill out the Punnett Square for the second generation. Careful
where you fill in!
G
g
G
G
G
g
g
g
Mendel and His Pea Plants
Fill out the Punnett Square for the second generation. Careful
where you fill in!
G
g
G
g
GG
Gg
Gg
gg
Mendel and His Pea Plants
What are the phenotypes for the genotypes inherited?
G
GG
G
g
green
pea
Gg
green
pea
g
Gg
green
pea
gg
yellow
pea
What is the frequency of
the genotypes?
GG appears 1 out of 4
times, or 25%.
Gg appears 2 out of 4
times, or 50%.
gg appears 1 out of 4
times, or 25%.
Mendel and His Pea Plants
How many different phenotypes are produced?
Two – green pea and yellow pea
How many different genotypes are produced?
Three – GG, Gg, and gg
Name the dominant genotype(s):
GG and Gg
What about recessive?
gg
Mendel and His Pea Plants
Exit question: Finish this Punnett Square.
G
g
g
g