Transcript Mendelian Genetics

Gregor Mendel
And The Genetic Revolution
Timothy G. Standish, Ph. D.
©1999 Timothy G. Standish
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).
©1999 Timothy G. Standish
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.”
Mendel’s work was rediscovered in 1900 by three
botanists:
– Carl Correns (Germany)
– Erich von Tschermak (Austria)
– Hugo de Vries (Holland)
©1999 Timothy G. Standish
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.
©1999 Timothy G. Standish
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:
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–
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–
–
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–
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
©1999 Timothy G. Standish
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
©1999 Timothy G. Standish
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
Anthers
Pea flower
Stigma
©1999 Timothy G. Standish
Why Peas?
By removing the anthers of one flower and
artificially pollinating using a brush, crosses
can be easily controlled in peas.
©1999 Timothy G. Standish
Why Peas?
By removing the anthers of one flower and
artificially pollinating using a brush, crosses
can be easily controlled in peas.
©1999 Timothy G. Standish
Why Peas?
By removing the anthers of one flower and
artificially pollinating using a brush, crosses
can be easily controlled in peas.
..
.........
©1999 Timothy G. Standish
Why Peas?
By removing the anthers of one flower and
artificially pollinating using a brush, crosses
can be easily controlled in peas.
..
.........
©1999 Timothy G. Standish
Why Peas?
By removing the anthers of one flower and
artificially pollinating using a brush, crosses
can be easily controlled in peas.
........
©1999 Timothy G. Standish
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
©1999 Timothy G. Standish
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
©1999 Timothy G. Standish
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
Heterozygous parents
were white
Homozygous
make gametes either
Gametes F1 Generation
from the P
generation
C C
c Cc Cc
c Cc Cc
parents can only one or the other allele
make gametes Fwith
2 Generation
one type of allele
The F1 Generation
is all heterozygous
C
C
c
CC Cc
c Cc cc
©1999 Timothy G. Standish
Mendel’s Results
Trait
F1 Results F2 Results
Dominent traits
round/wrinkled All Round
5,474
Round
1,850 wrinkled
mask
recessive
yellow/green All Yellow
6,022 Yellow 2,001 green
traits
full/constricted All Full
882 Full
299 constricted
Masked recessive
Pods
traits reappear
Seeds
green/yellow
axial/terminal
All Green
All Axial
428 Green
651 Axial
152 yellow
207 terminal
violet/white
All Violet
705 Violet
224 white
Tall/dwarf
All Tall
787 Tall
277 dwarf
Flowers
Stem
©1999 Timothy G. Standish
Mendel’s Results
F2 Results
F2 Ratios
Seeds
Seeds
l
5,474 Round 1,850 wrinkled 2.96:1 Round:wrinkled
6,022 Yellow 2,001 green
3.01:1 Yellow :green l
882 Full
299 constricted 2.95:1 Full:constricted
Pods
428 Green
651 Axial
Pods
152 yellow
207 terminal
Flowers
705 Violet
Flowers
224 white
Stem
787 Tall
2.82:1 Green:yellow
3.14:1 Axial:terminal
3.15:1 Violet:white
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?
Stem
277 dwarf
2.84:1 Tall:dwarf
©1999 Timothy G. Standish
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
©1999 Timothy G. Standish
Independent Assortment
As long as genes are on
different chromosomes,
they will assort
independently
TC Tc
tC
tc
TC
TTCC
TTCc
TtCC
TtCc
Tc
TTCc
TTcc
TtCc
Ttcc
tC
TtCC
TtCc
ttCC
ttCc
tc
TtCc
Ttcc
ttCc
ttcc
©1999 Timothy G. Standish
©1999 Timothy G. Standish