1. Mendel and His Pea Plants

2. 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

3. 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.

4. Mendel and His Pea Plants
wild wheat
wheat we eat
wild corn

5. 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.

6. 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.

7. 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.
pollen (sperm cells)
Plants can do this themselves. This is self-pollination.
pistil
Or you can take pollen from one plant and put it on the pistil of another. This is called cross-pollination.

8. 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

9. Mendel and His Pea Plants
Word
Definition
Picture
a plant that produces offspring with traits that are like the parents
True-breeding

10. 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!

11. Mendel and His Pea Plants
Word
Definition
Picture
when the pollen of one plant reaches the pistil of a flower on a different plant
Cross-pollination

12. 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.

13. Mendel and His Pea Plants
Word
Definition
Picture
blue flower
how a trait appears or is expressed (what it looks like)
Phenotype

14. 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.

15. Mendel and His Pea Plants
Word
Definition
Picture
section of a chromosome that has genetic information for one trait
Gene

16. Mendel and His Pea Plants
Word
Definition
Picture
blue flower
brown flower
different forms of a gene
Allele

17. Mendel and His Pea Plants
Word
Definition
Picture
Gg for green peas
the two alleles that control the phenotype of a trait
Genotype

18. 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…

19. 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?!?

20. 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.

21. Mendel and His Pea Plants
Word
Definition
Picture
allele that blocks another allele and is expressed in the phenotype
green pea color is dominant to yellow
Dominant trait

22. 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.

23. Mendel and His Pea Plants
Word
Definition
Picture
yellow peas are recessive
allele that is blocked by another allele
Recessive trait

24. 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.

25. 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 G

26. 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? g G
green, because there is a dominant allele (G) G

27. 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

28. 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 g

29. Mendel and His Pea Plants
These are the genotypes from the first daughter generation. What are the phenotypes? g g
What is the frequency of the genotypes?
G g
G g G
green pea
green pea
Gg appears 4 out of 4 times, or 100%.
G g
G g G
green pea
green pea

30. 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?

31. 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

32. 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 g

33. Mendel and His Pea Plants
What are the phenotypes for the genotypes inherited? G g
What is the frequency of the genotypes?
G G
G g G
green pea
green pea
GG appears 1 out of 4 times, or 25%.
G g
g g
Gg appears 2 out of 4 times, or 50%. g
green pea
yellow pea
gg appears 1 out of 4 times, or 25%.

34. 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

35. Mendel and His Pea Plants
Exit question: Finish this Punnett Square. G g g g