Gregor Mendel And The Genetic Revolution Timothy G. Standish, Ph. D.

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).

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

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.

Why Peas? Mendel used peas to study inheritance because: True breeding commercial strains were availible 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

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 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 Stigma Pea flower Anthers

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

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

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

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

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

Mendels Results When crossing purple flowered peas with white flowered peas, Mendel got the following results: In the first filial (F 1 ) generation all offspring produced purple flowers In the second generation (second filial or F 2 ): –705 purple –224 white Approximately a 3:1 ratio of purple to white

Interpreting Mendels Results Because the F 1 generation did not produce light purple flowers and because white flowers showed up in the F 2 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

Interpreting Mendels Results CC Cc cc In the F 1 generation, the white allele was hidden by the purple dominant allele In the F 2 generation, 1/4 of the offspring wound up with two copies of the white allele thus they were white Cc C c F 2 Generation Cc CC c c F 1 Generation Gametes from the P generation Heterozygous parents make gametes either one or the other allele The F1 Generation is all heterozygous Homozygous parents can only make gametes with one type of allele

Mendels Results Trait Seeds round/wrinkled yellow/green full/constricted Pods green/yellow axial/terminal Flowers violet/white Stem Tall/dwarf 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 F1 Results All Round All Yellow All Full All Green All Axial All Violet All Tall F2 Results 5,474 Round1,850 wrinkled 6,022 Yellow2,001 green 882 Full299 constricted 428 Green152 yellow 651 Axial207 terminal 705 Violet224 white 787 Tall277 dwarf F2 Results 5,474 Round1,850 wrinkled 6,022 Yellow2,001 green 882 Full299 constricted 428 Green152 yellow 651 Axial207 terminal 705 Violet224 white 787 Tall277 dwarf Dominent traits mask recessive traits Masked recessive traits reappear

Mendels Results F2 Results Seeds 5,474 Round1,850 wrinkled 6,022 Yellow2,001 green 882 Full299 constricted Pods 428 Green152 yellow 651 Axial207 terminal Flowers 705 Violet224 white Stem 787 Tall277 dwarf F2 Results Seeds 5,474 Round1,850 wrinkled 6,022 Yellow2,001 green 882 Full299 constricted Pods 428 Green152 yellow 651 Axial207 terminal Flowers 705 Violet224 white Stem 787 Tall277 dwarf F2 Ratios Seeds 2.96:1 Round:wrinkled 3.01:1Yellow:green 2.95:1Full:constricted Pods 2.82:1Green:yellow 3.14:1Axial:terminal Flowers 3.15:1Violet:white Stem 2.84:1Tall:dwarf F2 Ratios Seeds 2.96:1 Round:wrinkled 3.01:1Yellow:green 2.95:1Full:constricted Pods 2.82:1Green:yellow 3.14:1Axial:terminal Flowers 3.15:1Violet:white Stem 2.84:1Tall:dwarf l Ratios are not exactly 3:1 l How do we decide if the ratios are close enough to 3:1 to support and not reject our theory?

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

TcTc tCtC tctc TCTCt ct ct Ct CT cT cT CT C Independent Assortment TtCcTtCcTtCCTTCcTTCC TtccTtCcTtCcTTccTTCc ttCcttCCTtCcTtCcTtCC ttccttCcTtccTtCcTtCc As long as genes are on different chromosomes, they will assort independently