Gregor Mendel And The Genetic Revolution

1. Gregor MendelAnd The Genetic Revolution Timothy G. Standish, Ph. D.

2. Introduction- Gregor Mendel • Father of classical genetics. • Born Johan Mendel in 1822 to peasant family in the Czech village of Heinzendorf part of the Austro-Hungarian empire at the time. • Austrian Augustinian monk (Actually from Brunn which is now in the Czech Republic).

3. Gregor Mendel - Work • Starting in 1856 Mendel studied peas which he grew in a garden outside the Abbey where he lived. • Showed that the traits he studied behaved in a precise mathematical way and disproved the theory of "blended inheritance.” • Mendel’s work was rediscovered in 1900 by three botanists: • Carl Correns (Germany) • Erich von Tschermak (Austria) • Hugo de Vries (Holland)

4. Chromosomes:The Physical Basis of Inheritance • 1866 Mendel published his work • 1875 Mitosis was first described • 1890s Meiosis was described • 1900 Mendel's work was rediscovered • 1902 Walter Sutton, Theodore Boveri and others noted parallels between behavior of chromosomes and alleles.

5. Why Peas? • Mendel used peas to study inheritance because: • True breeding commercial strains were available • Peas are easy to grow • Peas have many easy to observe traits including: • Seed color - Green or yellow • Seed shape - Round or wrinkled • Pod color - Green or yellow • Pod shape - Smooth or constricted • Flower color - White or purple • Flower position - Axial or terminal • Plant size - Tall or dwarf

6. Pea flower Why Peas? • Pea flowers are constructed in such a way that they typically self fertilize • Because of this, it is relatively easy to control crosses in peas

7. Anthers Stigma Pea flower Why Peas? • Pea flowers are constructed in such a way that they typically self fertilize • Because of this, it is relatively easy to control crosses in peas

8. Why Peas? • By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas.

9. Why Peas? • By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas. Snip

10. . . . . . . . . . . . . Why Peas? • By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas.

11. . . . . . . . . . . . . Why Peas? • By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas.

12. . . . . . . . . Why Peas? • By removing the anthers of one flower and artificially pollinating using a brush, crosses can be easily controlled in peas.

13. Mendel’s Results • When crossing purple flowered peas with white flowered peas, Mendel got the following results: • In the first filial (F1) generation all offspring produced purple flowers • In the second generation (second filial or F2): • 705 purple • 224 white • Approximately a 3:1 ratio of purple to white

14. Interpreting Mendel’s Results • Because the F1 generation did not produce light purple flowers and because white flowers showed up in the F2 generation, Mendel disproved blended inheritance. • Mendel said that the parents had two sets of genes thus two copies of the flower color gene • Each gene has two varieties called alleles • In the case of the flower color gene the two alleles are white and purple

15. C C c C c C c c Heterozygous parents make gametes either one or the other allele Homozygous parents can only make gametes with one type of allele Gametes from the P generation F1 Generation F2 Generation The F1 Generation is all heterozygous Interpreting Mendel’s Results • In the F1 generation, the white allele was hidden by the purple “dominant” allele • In the F2 generation, 1/4 of the offspring wound up with two copies of the white allele thus they were white Cc Cc CC Cc Cc Cc Cc cc

16. Dominent traits mask recessive traits Masked recessive traits reappear Mendel’s Results Trait Seeds round/wrinkled yellow/green full/constricted Pods green/yellow axial/terminal Flowers violet/white Stem Tall/dwarf F1 Results All Round All Yellow All Full All Green All Axial All Violet All Tall F2 Results 5,474 Round 1,850 wrinkled 6,022 Yellow 2,001 green 882 Full 299 constricted 428 Green 152 yellow 651 Axial 207 terminal 705 Violet 224 white 787 Tall 277 dwarf

17. Mendel’s Results F2 Results Seeds 5,474 Round 1,850 wrinkled 6,022 Yellow 2,001 green 882 Full 299 constricted Pods 428 Green 152 yellow 651 Axial 207 terminal Flowers 705 Violet 224 white Stem 787 Tall 277 dwarf F2 Ratios Seeds 2.96:1 Round:wrinkled 3.01:1 Yellow :green 2.95:1 Full:constricted Pods 2.82:1 Green:yellow 3.14:1 Axial:terminal Flowers 3.15:1 Violet:white Stem 2.84:1 Tall:dwarf • Ratios are not exactly 3:1 • How do we decide if the ratios are close enough to 3:1 to support and not reject our theory?

18. Independent Assortment • When Mendel crossed peas and looked at two different traits, he discovered that the traits assorted independently • In other words, if he was looking at the height of the plants and the color of the flowers, all four possible combinations of height and flower color were produced: • Tall Purple • Tall white • dwarf Purple • dwarf white

19. TC Tc tC tc TC TTCC TTCc TtCC TtCc Tc TTCc TTcc TtCc Ttcc tC TtCC TtCc ttCC ttCc tc TtCc Ttcc ttCc ttcc Independent Assortment As long as genes are on different chromosomes, they will assort independently

20. The End