1. Meiosis and Punnett Square Notes

2. Primary Learning Objectives
To understand the differences between meiosis and mitosis.
To be able to use a Punnett square to
predict two parents’ offsprings’
phenotypic and genotypic
percentages for one trait.

3. Chromosomes
Where are they found?
Why are they important?

4. Chromosomes Found in the nucleus
Important because they contain the directions for making proteins.
What are Proteins?
And why are
Proteins so important?

5. Proteins The building blocks of all organisms.
Most cell organelles are made up mostly of proteins.

6. Proteins
The human body contains more than 100,000 different types of protein, each with its own function.
The type of proteins that are produced within an organism will determine
1. what an organism will look like
2. how it will behave

7. Back to the Chromosomes
Chromosomes contain the directions for which and how many proteins should be produced.
This information changes from organism to organism.
Therefore different organisms
have different numbers of
chromosomes.

8. Each type of organism (species) has a set number of chromosomes
Fruit Flies have 8 chromosomes
Humans have 46 chromosomes
Potatoes have 48 chromosomes
Note: The number of chromosomes is NOT dependent on the complexity of the organism.

9. The Structure of Chromosomes
are made of DNA

10. DNA
DNA stores the information for making proteins in a pattern, much like a book stores information in a pattern of words and letters.

11. An Analogy comparing Chromosomes and DNA
Chromosomes would be like a library and the sections of DNA, called genes, would be the books inside the library containing information for building proteins.

12. Reproduction
When an organism reproduces it has to pass on the information about how to build proteins
In other words the chromosomes must be duplicated and passed on to the next generation of organisms.
There are two ways
in which this is done.

13. Two Types of Reproduction
Asexual
Sexual
We have learned about one type of reproduction already!

14. Asexual Reproduction Mitosis is one type of asexual reproduction
Mitosis is a form of asexual reproduction because offspring have DNA that is identical to their parents.
In asexual reproduction there is only one parent.

15. Mitosis is One Example of Asexual Reproduction
Offspring
Parent
Cell
One Parent cell produces 2 identical offspring cells

16. Sexual reproduction usually involves two different parents.
Sexual reproduction involves the combining of DNA from two separate cells to begin a new organism.

17. Sexual Reproduction
The two cells that merge during sexual reproduction are special sex cells called GAMETES.
In most living things, gametes come in two different forms: Male and Female.

18. Sexual Reproduction GAMETES Egg and sperm cells are gametes.
The merging of two gametes is called FERTILIZATION.
The result of fertilization is a ZYGOTE.

19. Sexual Reproduction
Sperm
Fertilization
Gametes
Egg
Zygote
Gametes have ½ the normal number of chromosomes. When fertilization occurs, the resulting zygote has a complete set of chromosomes to make a new organism!

20. Sexual Reproduction Gametes DO NOT divide by the process of mitosis.
IF an egg cell contained 46 chromosomes and a sperm cell contained 46 chromosomes then the new offspring would have 92 chromosomes.
THAT’S TOO MUCH
INFORMATION!!

21. Sexual Reproduction
Humans gametes (egg & sperm cells) contain only 23 chromosomes instead of the normal 46.
HOW DID
THAT HAPPEN?

22. Sexual Reproduction
Instead of going through mitosis (Where the same number of chromosomes are produced) Gametes go through the process of MEIOSIS (Where ½ the number of chromosomes are produced)

23. Meiosis

24. Mitosis
Meiosis

25. Punnett Squares

26. Consider a plant with the following phenotype and genotype.
Phenotype: red flowers
Genotype: RR (pure dominant)
If a sperm (pollen) from this plant fertilizes (pollinates) an egg (ovule from a plant that has
Phenotype: white flowers
Genotype: rr (pure recessive)
What are the possible phenotypes and genotypes of the offspring?

27. Genotypes: Rr
Phenotypes: Red flowers

28. Male: phenotype: red flowers genotype: Rr (hybrid)
What if…
Male: phenotype: red flowers
genotype: Rr (hybrid)
Fertilizes (pollinates)
Female: phenotype: red flowers
What are the possible phenotypes and genotypes of the offspring?

29. Genotypes: RR, Rr, rr
Phenotypes: Red or White flowers

30. There is an easy way to determine the answers for the last two questions. To make it easier to answer questions that ask about predicting the possible phenotype and genotypes of offspring you can use what is called a Punnett square.
Let’s use the second question to show you how much easier it can be.

31. Male: phenotype: red flowers genotype: Rr (hybrid)
What if…
Male: phenotype: red flowers
genotype: Rr (hybrid)
Fertilizes (pollinates)
Female: phenotype: red flowers
What are the possible phenotypes and genotypes of the offspring?

32. A Punnett square looks like the following. Possible Female Genes R r
Possible R
Male
Genes r

33. Now you can line up the possible combinations of genes.
Let’s take a look at how the answers in each box are determined.
Possible Female Genes
R r
Possible R
Male
Genes r

34. Now looking at the Punnett square it is easier to determine the possible genotypes and phenotypes.
Possible Female Genes
R r
Possible R
Male
Genes r RR Rr rr

35. Genotypes: RR, Rr, rr
Phenotypes: Red or White flowers

36. Using a Punnett square you can also predict what percentage (%) of offspring will have which phenotypes and genotypes.

37. What percentage of the offspring would be pure dominate, pure recessive, and hybrid?RR Rr rr

38. What percentage of the offspring would be red flowers and white flowers?RR Rr rr

39. Punnett Square Problem Solving
Today we will be predicting the genotypic and phenotypic outcomes of hypothetical mice breeding.

40. Problem 1
What would the possible phenotypic and genotypic outcomes be of the offspring if two black mice, both with the genotype (BB) were mated (crossed)?

41. Problem 2
What would the possible phenotypic and genotypic outcomes of the offspring be if a pure dominant black mouse was crossed with a hybrid?

42. Problem 2, Part II What is the phenotype of the hybrid?
What percentage of offspring would you predict to be pure dominant?
What percentage of offspring would you predict to be pure recessive?
What percentage of offspring would you predict to be hybrid?

43. Problem 2, Part III
What percentage of the offspring would you predict to be black?
What percentage of the offspring would you predict to be white?

44. Problem 3
Create a Punnett square to determine the phenotypic percentage of black and white offspring mice if a pure dominant mouse is mated with a pure recessive mouse.
Part II
Determine the genotypic percentage of offspring that will be pure dominant, pure recessive and hybrid.

45. Problem 4
Predict the phenotypic and genotypic percentages of offspring if a hybrid mouse if crossed with a pure recessive mouse.

46. Problem 5
Predict the phenotypic and genotypic percentages of offspring if two hybrid mice are crossed.