Mendel and His Pea Plants - PowerPoint Presentation

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Mendel and His Pea Plants

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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 breedingSlide3

Mendel and His Pea Plants

Selective breeding is agriculture! It is breeding plants or animals for specific traits.

What is selective breeding?

pest resistant corn

stronger oxen

sheep with thicker wool

People have been doing selective breeding for thousands of years.

Can you think of others?Slide4

Mendel and His Pea Plants

w

ild

w

heat

w

heat we eat

wild cornSlide5

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. Slide6

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

.Slide7

Mendel and His Pea Plants

Another great reason to use pea plants is you can control which plants are reproduced.

For plants to reproduce, pollen needs to get to a plant’s pistil.

Plants can do this themselves. This is self-pollination.

Or you can take pollen from one plant and put it on the pistil of another. This is called cross-pollination.

pistil

pollen (sperm cells)Slide8

Mendel and His Pea Plants

Mendel started with

true-breeding

plants

True-breeding plants self-pollinate

Offspring are the same as the parent

What you start with is what you getSlide9

Mendel and His Pea Plants

Word

Definition

Picture

True-breeding

a plant that produces offspring with traits that are like the parents Slide10

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!Slide11

Mendel and His Pea Plants

Word

Definition

Picture

Cross-pollination

when the pollen of one plant reaches the pistil of a flower on a different plantSlide12

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

.Slide13

Mendel and His Pea Plants

Word

Definition

Picture

Phenotype

how a trait appears or is expressed (what it looks like)

blue flowerSlide14

Mendel and His Pea Plants

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.

But what makes something look a certain way? What gave Mendel yellow peas or white flowers?

Genotypes!

The combination of these

alleles

is your

genotype

.Slide15

Mendel and His Pea Plants

Word

Definition

Picture

Gene

section of a chromosome that has genetic information for one traitSlide16

Mendel and His Pea Plants

Word

Definition

Picture

Allele

different forms of a gene

blue flower

brown flowerSlide17

Mendel and His Pea Plants

Word

Definition

Picture

Genotype

the two alleles that control the phenotype of a trait

Gg

for green peasSlide18

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…Slide19

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 2

nd generation.

Wait! What?!?

+

2nd generation

+Slide20

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.Slide21

Mendel and His Pea Plants

Word

Definition

Picture

Dominant trait

allele that blocks another allele and is expressed in the phenotype

green pea color is dominant to yellowSlide22

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

.Slide23

Mendel and His Pea Plants

Word

Definition

Picture

Recessive trait

allele that is blocked by

another allele

yellow peas are recessiveSlide24

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

.Slide25

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.

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.

G

GSlide26

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

alleles

would be _______.

gg

Remember, we use the code based on the dominant

genotype

, so lowercase “

g

” means yellow. If the

genotype

were

Gg

, what color would the peas be?

green, because there is a

dominant allele (

G)

G

g

g

GSlide27

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

GSlide28

Mendel and His Pea Plants

Now, the other set of genes.

Dominant alleles

are always listed first.

G

G

G

G

g

g

g

G

g

g

G

gSlide29

Mendel and His Pea Plants

These are the

genotypes

from the first daughter generation. What are the

phenotypes

?

G

g

G

g

G

g

G

g

green pea

green pea

green pea

green pea

G

g

g

G

What is the frequency of the

genotypes

?

Gg

appears 4 out of 4 times, or 100%.Slide30

Mendel and His Pea Plants

What if we take two daughter plants from the first generation and cross them?

What do you think will happen?

What are the

genotypes

for the mother and father plants?

What are the

phenotypes

for the peas?

Gg

greenSlide31

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

GSlide32

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

g

G

g

GSlide33

Mendel and His Pea Plants

What are the

phenotypes

for the

genotypes

inherited?

g

G

g

g

G g

G

g

G G

green pea

yellow pea

green pea

green pea

g

G

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%.Slide34

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?

ggSlide35

Mendel and His Pea Plants

Exit question: Finish this

Punnett

Square.

G

g

g

g