1. The Work of Gregor Mendel Or, why peas are awesome

2. The Man Gregor Mendel (1822-1884) was a monk who lived in what is now the Czech Republic. He was a painfully shy man who loved science. He tended the Abbey garden and found time to do breeding experiments on the common pea plant. He found 7 pea plant traits that he wanted to experiment with.

3. Pea Traits Gregor Mendel found that peas displayed these traits in one way or another. Never a mixture.

4. Pea Traits For example, if a pea plant had white and wrinkled pods, all its pods were white and wrinkled.

5. Why were peas totally awesome for his experiments? Because they could fertilize themselves. Remember: – Fertilization is when male and female reproductive cells join to make a new cell. Question: What ploidy are the male and female reproductive cells? What ploidy is the newly formed cell?

6. Why were peas totally awesome for his experiments? Because they could fertilize themselves. Remember: – Fertilization is when male and female reproductive cells join to make a new cell. Question: What ploidy are the male and female reproductive cells?: Haploid What ploidy is the newly formed cell?: Diploid

7. The Humble Pea

8. Fertilization

9. Vocab Review! Fertilization: When male and female sex cells unite to form a new cell. Trait: A specific characteristic of an individual Genes: Factors passed from parent to offspring that code for traits.

10. How do you start an experiment that will change modern genetics? Mendel started with true-breeding plants. These plants could cross with themselves and always produce offspring that looked identical to the parent.

11. What does true breeding mean? True breeding plants always produce babies that look like them. Always. All their genes are the same at every place on the chromosome. These are very important in agricultural science.

12. Traits and alleles Traits:

13. Traits and Alleles Gene: Fur color Allele: Black, brown or white Coat color is an obvious trait, and is called the phenotype. The alleles can be abbreviated with single letters and the allele (or genetic) makeup is called the genotype.

14. Genes and Alleles So for any one gene, like hair color, every person has two alleles: one that came from their mom, and one that came from their dad. If dad has genotype with two different alleles, he’ll put one into each of two sperm. HH HH Parental Genotype

15. Alleles and Dominance In his experiments with peas, Mendel found that some alleles were dominant while others were recessive. – A dominant allele is always expressed when it’s present. – A recessive allele is only expressed when it’s partner is another recessive allele.

16. Dominant and Recessive Alleles

17. Dominant and Recessive alleles The following picture is of a family. The mother has blonde hair, the father has brown hair but both children have red hair. This is because blonde and brown alleles are dominant to red alleles.

18. Alleles and Dominance

19. Genotypes What do you think the genotypes for the following people are if the alleles are the following Bla = Black > Br = Brown > BL = Blonde > R= Red HINT: Everyone has two alleles, and the parents have to pass along just one to the children. Mother in the picture: Father in the picture: Daughter in the picture: Son in the picture:

20. Genotypes What do you think the genotypes for the following people are? Mother in the picture: Bl R Father in the picture: Br R Daughter in the picture: R R Son in the picture: R R

21. Dominance The principle of dominance states that some alleles are dominant and others are recessive. What does that mean in plain language? – In plain language, this means that if two alleles are present in an organism, one will always be the “winner” and express a trait, the other one will be hidden by the dominant one.

22. A Note About Vocab: We use some abbreviations to make writing about alleles simpler. Choose the trait that is expressed by the dominant allele. We usually write the Dominant allele as a capital letter, and the recessive allele as a lowercase version of that same letter.

23. Example In peas, tall plants are dominant to short plants. Since tall is the dominant trait, we choose T to represent the tall allele, and t to represent the short allele.

24. Vocab continued: Now that we can write alleles, there are some other descriptive science words that we can use to talk about genotypes. Homozygous is a word that means you have two of the SAME alleles. Heterozygous is a word that means you have two different alleles. It is the same as the word “hybrid.”

25. Vocab EXAMPLE: if a plant has genotype BB, we would say that plant was homozygous dominant. EXAMPLE: if a plant has genotype bb, we would say that plant was homozygous recessive. EXAMPLE: if a plant has genotype Bb, we would say that plant was heterozygous.

26. Solving Genetics Problems. To answer questions about how alleles are passed along, we can use a tool called a punnett square. Punnett squares are good to help us predict all the possible outcomes of a mating event, or cross.

27. Punnett Squares For example, say you have two pea plants. One is tall with genotype TT and the other is short with genotype tt. First, we find all the possible gametes for the pea plants. TT tt T tt T

28. Punnett Squares Then, we put the gametes on the Punnett square to find all the possible combinations: T TT tt T t

29. Probability and Punnett Squares Once we have the Punnett square completed, we can ask questions about the liklihood that certain outcomes will happen. Probabilities are written as percentages or fractions.

30. Probability Practice Tt tT TT Tt tt Tt Using the punnett square to the side, what are the probabilities? That an offspring will have genotype TT? That the offspring will have a tall phenotype? That the offspring will have a recessive genotype?

31. Probability Practice Tt tT TT Tt tt Tt That an offspring will have genotype TT? ¼ or 25% That the offspring will have a tall phenotype? ¾ or 75% That the offspring will have a recessive genotype? ¼ or 25%