Introduction to Genetics: The Work of Gregor Mendel

4. Honors Biology Unit 5 / Chapter 11 Powerpoint #1 Introduction to Genetics:The Work of Gregor Mendel

5. Gregor Mendel was born in 1822 in the Czech Republic • Studied Science and Mathematics at the University of Vienna • Spent the next 14 years teaching high school and working at a monastery in the garden

6. Mendel noticed that the SAME type of plant could have VARIATIONS, or differences, these are the variations he noticed:

8. Mendel wanted to breed the pea plants together in different combinationsto see what the offspring (seedlings) would look like. After Mendel noticed these variations he decided to do an experiment of his own.

11. Describe how Mendel prevented self-pollination and controlled cross-pollination in pea plants: He cut off the male parts of one flower, then dusted the stigma with pollen from a second flower. Why did he want to do this?He wanted plants with specific traits to breed with one another. Techniques of Mendel

12. Genetics: study of heredity (how traits pass from one generation to the next) True-breeding: if allowed to self-pollinate, produce offspring identical to self Self-pollination: pollen from one flower fertilizes egg cells in same flower Cross-pollination: pollen from one flower fertilizes egg cells in a different flower Terminology

13. Trait: specific characteristic that varies from one individual to another Example: Hair color, Eye color, height P generation:parental generation Terminology

14. F1 generation:first generation of offspring (first filial generation) (AKA kids of parents) F2 generation:second generation of offspring (offspring of F1 plants) (AKA grandkids of parents) Terminology

15. Hybrid:offspring of crosses between parents with different traits. Example: Cross pollinate a red flower and a white flower. Seedlings=hybrid X =

16. Hybrid Cars Gas + Electric

17. Gene:segment of DNA that determines a trait Alleles:different forms of a gene (ex: Height: tall gene, or short gene) Terminology

18. Allele

19. Principle of dominance: • dominant trait always seen when dominant allele is present; recessive trait only seen when no dominant allele is present

20. Recessive allele: allele that is masked (hidden) when dominant allele is present • Allele for blue eyes Dominant allele: allele that is always expressed when it is present • Allele for brown eyes Terminology

21. A capitalletter represents the dominant allele. A lower caseletter represents the recessive allele. Example: Pea plant height – Tall: T Short: t Notation

23. Segregation of alleles: separation of alleles during gamete production (meiosis) Gametes: sex cells (egg, sperm) Note: all body cells contain two copies of each chromosome (and therefore two copies of each gene) – one copy is from the male parent and one copy is from the female parent During meiosis, each gamete (egg or sperm cell) receives only one copy of each chromosome (and gene (allele)), thus the two copies of each gene are separated. Mechanics

24. Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall Pea Plant Traits

25. Parents Long stems  short stems Purple flowers  white flowers Green pods  yellow pods Round seeds  wrinkled seeds Yellow seeds  green seeds First Generation All long All purple All green All round All yellow Second Generation 787 long: 277 short 705 purple: 224 white 428 green: 152 yellow 5474 round: 1850 wrinkled 6022 yellow: 2001 green Mendel’s Observations • 1. In the first generation of each experiment, how do the characteristics of the offspring compare to the parents’ characteristics? • 2. How do the characteristics of the second generation compare to the characteristics of the first generation?

26. Mendel’s Experiment P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short tt TT Tt Tt tt TT Tt Tt

28. Why are there no white flowers in the F1 generation? The purple parent has 2 purple alleles and the white parent has 2 white alleles. The F1 plants each have one purple and one white allele – the purple allele is dominant so it masks the white allele. Why are there no light purple flowers in the F1 generation? Traits do not blend. Mechanics Explain why the offspring of a true-breeding pea plant with white flowers and a true-breeding pea plant with purple flowers are all purple

29. How did Mendel show that the recessive allele had not disappeared in the F1 generation? When he cross-pollinated plants from the F1 generation, the recessive trait showed up again in the F2 generation.  This showed Mendel that there must be two factors (genes) controlling each trait – one is dominant and masks the other (which is recessive). Mendel’s Experiment

30. Mendel did his work before DNA! Pea Plant DNA (Electron Microscope)