Gregor Mendel And The Genetic Revolution Timothy G. Standish, Ph. D.
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Transcript of Gregor Mendel And The Genetic Revolution Timothy G. Standish, Ph. D.
Gregor MendelGregor MendelAnd The Genetic RevolutionAnd The Genetic Revolution
Timothy G. Standish, Ph. D.
Introduction- Gregor MendelIntroduction- 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 - WorkGregor 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.”
Mendel’s work was rediscovered in 1900 by three botanists:– Carl Correns (Germany)
– Erich von Tschermak (Austria)
– Hugo de Vries (Holland)
Chromosomes:Chromosomes:The Physical Basis of InheritanceThe 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?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?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?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
StigmaPea flower
Anthers
Why 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?Why Peas? By removing the anthers of one flower and
artificially pollinating using a brush, crosses can be easily controlled in peas.
Why 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?Why Peas? By removing the anthers of one flower and
artificially pollinating using a brush, crosses can be easily controlled in peas.
. .... .
...
...
Why Peas?Why Peas? By removing the anthers of one flower and
artificially pollinating using a brush, crosses can be easily controlled in peas.
.... ....
Mendel’s ResultsMendel’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
Interpreting Mendel’s ResultsInterpreting 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
Interpreting Mendel’s ResultsInterpreting Mendel’s Results
CC
Cc
Cc
cc
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
C c
C
c
F2 GenerationF2 Generation
Cc
Cc
Cc
Cc
C C
c
c
F1 GenerationF1 GenerationGametes 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
Mendel’s ResultsMendel’s ResultsTraitSeeds
round/wrinkledyellow/greenfull/constricted
Podsgreen/yellowaxial/terminal
Flowersviolet/white
StemTall/dwarf
TraitSeeds
round/wrinkledyellow/greenfull/constricted
Podsgreen/yellowaxial/terminal
Flowersviolet/white
StemTall/dwarf
F1 Results All RoundAll YellowAll Full
All GreenAll Axial
All Violet
All Tall
F1 Results All RoundAll YellowAll Full
All GreenAll Axial
All Violet
All Tall
F2 Results 5,474 Round 1,850 wrinkled6,022 Yellow 2,001 green 882 Full 299 constricted
428 Green 152 yellow651 Axial 207 terminal
705 Violet 224 white
787 Tall 277 dwarf
F2 Results 5,474 Round 1,850 wrinkled6,022 Yellow 2,001 green 882 Full 299 constricted
428 Green 152 yellow651 Axial 207 terminal
705 Violet 224 white
787 Tall 277 dwarf
Dominent traits mask recessive traits
Masked recessive traits reappear
Mendel’s ResultsMendel’s ResultsF2 Results Seeds5,474 Round 1,850 wrinkled6,022 Yellow 2,001 green 882 Full 299 constricted
Pods428 Green 152 yellow651 Axial 207 terminal
Flowers705 Violet 224 white
Stem787 Tall 277 dwarf
F2 Results Seeds5,474 Round 1,850 wrinkled6,022 Yellow 2,001 green 882 Full 299 constricted
Pods428 Green 152 yellow651 Axial 207 terminal
Flowers705 Violet 224 white
Stem787 Tall 277 dwarf
F2 Ratios Seeds2.96:1 Round:wrinkled3.01:1 Yellow:green2.95:1 Full:constricted
Pods2.82:1 Green:yellow3.14:1 Axial:terminal
Flowers3.15:1 Violet:white
Stem2.84:1 Tall:dwarf
F2 Ratios Seeds2.96:1 Round:wrinkled3.01:1 Yellow:green2.95:1 Full:constricted
Pods2.82:1 Green:yellow3.14:1 Axial:terminal
Flowers3.15:1 Violet:white
Stem2.84:1 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?
Independent AssortmentIndependent 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
Tc
tC
tc
TC
t ct CT cT C
Independent AssortmentIndependent Assortment
TtCcTtCCTTCcTTCC
TtccTtCcTTccTTCc
ttCcttCCTtCcTtCC
ttccttCcTtccTtCc
As long as genes are on different chromosomes, they will assort independently