Gregor Mendel conducted experiments in the 1860s crossing different varieties of peas to study inheritance of traits. He observed that traits were passed down to offspring in predictable patterns, either dominantly or recessively. This work established foundations of genetics but was not widely recognized until the early 1900s. At the time of Mendel's work, cell structures like chromosomes were just beginning to be described microscopically, and their functions in heredity were not understood. Since Mendel, chromosome behavior during cell division has been shown to explain his laws of inheritance, and molecular genetics has revealed chromosomes contain genes on DNA that determine traits.

1. Mendel and his
time in the light
of cytogenetics
Trude Schwarzacher
University of Leicester
Department of Genetics
TS32@le.ac.uk
Gregor Mendel
(1822-1884)
www.molcyt.com
UserID/PW ‘visitor’

2. Hugo Iltis
‘Few publications have so enduringly and variously
influenced science as had the short monograph
[Versuche über Pflanzenhybriden] by the Augustinian
monk of Brünn [now Brno], Pater Gregor Mendel.
Forgotten for decades, within a few years after its
rediscovery it gave a mighty impetus to the doctrine
of heredity; and as Mendelism, his teaching had now
become the central theme of biological research as
well as the foundation of manifold practical
application’
Mendel’s life
(The Life of Mendel,1966)

3.  Mendel’s life
 Mendel’s experiments
 Why was he forgotten?
 What was known about chromosomes
at the time of Mendel?
 Mendel’s rediscovery at 1900
 How has chromosome biology
developed since
 Some examples from our own research
related to Mendel and plant
hybridization
Overview

4. 20 July 1822: born as Johann Mendel, Heinzendorf
bei Odrau, Austrian Empire (now Hynčice, Czech
Republic)
1840 – 1843: practical and theoretical philosophy
and physics at the University of Olomouc
Mendel’s life

5. 1843: joined as Pater Gregor the Augustinian
Monastery, Brünn (now Brno)
1847: ordained priest
1851-1853: Natural history at the University of
Vienna under Franz Ungar (professor of plant
physiology) and Christian Doppler (professor of
physics)
1853 onwards: supply teacher at Brno; he failed the
exam to become a certified teacher twice
1857-1864: Experiments with peas
Spring 1865: presented the results and
generalizations at two meetings of the Natural
History Society of Brünn
Mendel’s life

6. 1866: The papers were printed in the Proceedings
of the Society distributed in Europe and America
1866: Mendel consults Karl Wilhelm Nägeli of
Munich, leading botanist of the time. Nägeli does
not understand the significance of Mendel’s results
and laws of heredity
1868: Becomes abbot; and has decreasing time for
scientific activities
1869: Results on Hieraceum
6 January 1884: died at the age of 61
Mendel’s life

7. Mendel
Memorial in
Brno
Mendel’s life
Pat Heslop-Harrison in 2001
Jack Heslop-Harrison
in 1933

8.  Mendel’s life
 Mendel’s experiments
 Why was he forgotten?
 What was known about chromosomes
at the time of Mendel
 Mendel’s rediscovery
 How has chromosome biology
developed since
 Some examples from our own research
Overview

9. But Mendel does not
mean hybrids
between two
species, he means
between two
different types or
variants
“…
the regularity with
which the same
hybrid forms
resulted,
every time
fertilization between
the same species
occurred, gave the
incentive to further
controlled
experiments.”

10. Experiments with peas
Crossing (making hybrids with) varieties with clear and
different characters or traits
Drawing from many websites including
http://guestblog.scientopia.org/2012/08/03/mud-sticks-especially-if-you-
are-gregor-mendel/

11. Experiments with peas
Law of segregation

12. Experiments with peas
Law of
independent
assortment

13. Experiments with peas Defined the terms
recessive and dominant
Spoke of invisible ‘factors’ -
now called genes –
that were responsible for the
visible traits

15. Genetic location of Mendel's seven characters on pea linkage groups. Yellow versus
green cotyledons II/ii on linkage group (I); seed coat (and flower) colour AA/aa on
linkage group (II); tall versus dwarf plants (LeLe/lele) on linkage group (III); difference in
the form of the ripe pods (PP/pp or VV/vv) on linkage groups (III) and (VI), respectively;
difference in the position of the flower (FasFas/fasfas or FaFa/fafa) on linkage
groups (III) or(IV), respectively; round versus wrinkled (RR/rr) on linkage group (V); and
colour of unripe pod (GpGp/gpgp) on linkage group (V).
The types of
lesion in
Mendel's mutants
are various:
transposon
insertion (r),
missense
mutation (le-1),
splice variant (a)
and amino acid
insertion (i).
Ellis et al. 2011: Mendel, 150 years on. Trends in Plant Science 11:590-596.

16. 2010, doi:10.1371/journal.pone.0013230

17. Conclusions/Significance:
 Identification of the pea genes A that is the factor determining
anthocyanin pigmentation in pea
 The A gene encodes a bHLH transcription factor.
 The white flowered mutant allele most likely used by Mendel is a
simple G to A transition in a splice donor site that leads to a mis-
spliced mRNA with a premature stop codon

19. The wrinkled-seed mutant (rr) of pea (Pisum sativum L.) arose through
mutation of the gene encoding starch-branching enzyme isoform I (SBE1)
by insertion of a transposon-like element into the coding sequence.
Starch amount and amylopectin are reduced and as a consequence
sucrose level is higher that causes increased uptake of water. When the
seed tries the wrinkled phenotype results.

20.  Mendel’s life
 Mendel’s experiments
 Why was he forgotten?
 What was known about chromosomes
at the time of Mendel
 Mendel’s rediscovery
 How has chromosome biology
developed since
 Some examples from our own research
Overview

21. Mendel’s experiments
Mendel’s 1866 paper was cited only three times
over the next thirty-five years.
 Was Mendel ahead of his time?
 Did he have bad luck?
 Boring title and Mendel did not sell his theory
well.
 Mislead by Nägeli to work on Hieraceum that
did not prove his theory
 His paper was seen as essentially about
hybridization rather than inheritance

22.  His paper was seen as essentially about
hybridization rather than inheritance.
 Blended inheritance was the accepted
theory of inheritance where traits from each
parent are averaged together.
 not so different from what we now know to be
the case for multiple genes and quantitative
trait loci (QTL).
 Mendelian discontinuous inheritance applies
to single genes only.
Inheritance

23.  Mendel’s life
 Mendel’s experiments
 Why was he forgotten?
 What was known about chromosomes
at the time of Mendel
 Mendel’s rediscovery
 How has chromosome biology
developed since
 Some examples from our own research
Overview

24. micro.magnet.fsu.edu/primer/museum/hooke.html
First
microscope
observed cells

25. Compound microscope
The lens closest to the object, called the Objective, is
used to enlarge and invert the object into a 'real'
image.
The lens closest to the eye called the Eyepiece or Ocular
acts essentially as a simple magnifier, used to view
the image formed by the objective. The simple
magnifier is a converging lens placed in front of the
eye that increases the size of the image formed by
the retina.
www.math.ubc.ca/.../lewis/project.html
The compound microscope, in its
simplest form is a system of two
converging lenses used to look at
very small objects at short distances.
E. Leitz,
Wetzlar,
Germany,
1894

26. Modern microscope
www.math.ubc.ca/.../lewis/project.html
E. Leitz,
Wetzlar,
Germany,
1894
Axioimager

27. Recording chromosome images
 Drawings
 Photography
(1950-1980s)
 Black and white
 Colour
 Digital images
(1990s, now)
 CCD cameras
www.usyd.edu.au/.../cmicrodesign.shtml
http://www-unix.oit.umass.edu/~coreya/yashica/micadpt.jpg
First photograph: 1826,
Eastmann (1884): film as known today. Microphotography 1920/30.

28. Chromosomes
Early 19th century
Cells and nuclei simply
pinched in half to
divide
Anton Schneider
(1873)
First scientist to
describe clearly the
process of mitosis and
the involvement of the
‘chromatic nuclear
figure’

29. Eduard Strassburger (1875)
Gives clear and detailed descriptions of
cell division in plants
Walther Flemming (1879-1882)
Describes ‘Mitosis’ in animal cells
Discovers lampbrush chromosomes
Balbiani (1880)
Polytene chromosomes
Chromosome

30. Flemming 1882

31. Continuity of chromosomes
throughout cell division
Flemming 1882

32. Orientation of
chromosomes
within
interphase
 Rabl (1885)
 Rabl orientation
Salamandra maculata

33. 1B/1R wheatWheat containing chromosome 1RS
Schwarzacher et al. 1992

34. Metaphase I
Telomere
Centromeres
Interphase
Rye
Schwarzacher 2000

35. Gregor Mendel (1865)
Formulated his laws of heredity without
the knowledge of chromosomes
Wilhelm Waldeyer (1888)
Introduces the term ‘chromosome’
Weismann (1887)
Puts forward ‘chromosome theory of
inheritance’
1900: When Mendel was rediscovered, it became
clear that the behaviour of chromosomes at cell
division (mitosis and particular meiosis) was
exactly what was needed to explain the
distribution of hereditary factors
Waldeyer

36. Who and how was he
rediscovered
Mendel’s laws were rediscovered
independently within two months of each
other in Spring of 1900 by Hugo de Vries
and Carl Correns, and to some extend the
Austrian Erich von Tschermak.
Following their publications, Mendel’s results
were replicated and genetic linkage
formally described.
Rediscovery

37.  Mendel’s life
 Mendel’s experiments
 Why was he forgotten?
 What was known about chromosomes
at the time of Mendel
 Mendel’s rediscovery
 How has chromosome biology
developed since
 Some examples from our own research
Overview

38. Bateson (1916)
Described the concept of the gene
Feulgen and Rossenbock (1924)
Demonstrated the presence of DNA in
chromosomes by histochemical
staining
Watson and Crick (1953)
Structure of DNA
Early studies on chromosomes
were in insects and plants
Morgan and his students (Drosophila;
linkage groups)
Barbara McClintock (maize,
transposable elements)
Number of chromosomes in
human was not established until
1956 (J. Tijo and A. Levan)
Chromosomes, genes and DNA

39. Fluorescent in situ hybridization (FISH)

40. FISH 1985 onwards
Beta vulgaris
Propidium idode
FITC
Images from molcyt.com (upper row) and chrombios.com (lower row)

41. Wheat, Hieraceum
and Petunia
Polyploid
and diploid
hybrids
Oil seed rape, Brassica napus
Petunia
hybrida
P. axillaris
Hieraceum
Wheat trials

42. Triticale
wheat x rye
hybrid
Schwarzacher et al 1989, 1992
Total genomic DNA labels chromosomes
according to their genome origin
2n=6x=42
AABBRR
Annals of Botany 64, 315-324 and Theoretical and Applied Genetics 84, 778-786.

43. Rye and the genus Thinopyrum,
including wild goat grasses and wheat
grasses, has proven an excellent
source for disease and biotic stress
resitance
Schwarzacher 2000

44. Six populations of wheat lines that include an alien
chromosome arm from Thinopyrum intermedium carrying
WSMV resistance (Wsm-1 gene)
Characterization of new sources of Wheat
streak mosaic virus resistance
WSMV resistant and susceptible lines in field trials
Bob Graybosch, USDA-ARS, University of Nebraska, USA
Wheat ‘Mace’: Journal of Plant Registrations 3(1): 51-56.doi: 10.3198/jpr2008.06.0345crc
4D T4DL*4Ai#2S
DAPI Afa Thin all
(blue) (green) (red)

45. Some lines also carry a
Thin or rye fragment on
chromosome 1B
Th. intermedium
DNA
pSc119.2/CS13
Rye DNA
dpTa1/Afa
The whole 1RS arm correlates
with WSMV resistance in the
absence of 4D and when together
with 4D enhances resistance
Ali, Graybosch, Hein, Heslop-Harrison, and Schwarzacher 2015

46. Hieraceum
• Genus Hieraceum
• Hawkweed (German Habichtskraut)
• Family Asteraceae (Compositae)
• Closely related to Taraxacum (Dandelion)
• Probably 1,000+ species
• Classification notoriously difficult with a lot of minor
geographical variation
Most reproduce
exclusively asexually
by means of seeds
that are genetically
identical to their
mother plant
(apomixis or
agamospermy)
Rubar Salih, Richard
Gornall and Pat Heslop-
Harrison

47. Hieraceum
Taxon Section Chr
number
Ploidy Identifier
code
Source
H.amaurostictum Walter Scott &
R.C.Palmer
Alpestria 2n=36 4x Hama01 Semblister
H.attenuatifolium P.D.Sell & C.West Alpestria 2n=36 4x Hatt02 Laxo Burn
H.australis (Beeby)Pugsley Alpestria 2n=36 4x Haus03 Burrafirth area, Unst
H.breve Beeby Alpestria 2n=36 4x Hbre04 Ronas Voe
H.difficile P.D.Sell & C.West Alpestria 2n=36 4x Hdif05 Okraquoy
H.dilectum P.D.Sell & C.West Alpestria 2n=36 4x Hdil06 Laxo
H.gratum P.D.Sell & C.West Alpestria 2n=36 4x Hgra08 Burra Firth, Unst
H.hethlandiae (F.Hanb.) Pugsley Alpestria 2n=36 4x Hhet09 Mavis Grind
H.northroense Pugsley Alpestria 2n=27 3x Hnor11 Burravoe, North Roe
H.pugsleyi P.D.Sell & C.West Alpestria 2n=36 4x Hpug12 Whale Firth, Yell
H.spenceanum Qalter Scott &
R.C.Plamer
Alpestria 2n=36 4x Hspe14 Sandness
H.subtruncatum Beeby Alpestria 2n=36 4x Hsubt16 Scarvister, West Mainland
H.vinicaule P.D.Sell & C.West Alpestria 2n=27 3x Hvin17 Whale Firth
H.zetlandicum Beeby Alpestria 2n=36 4x Hzet18 Isbister, North Roe
H.scottii P.D.Sell Oreadea 2n=36 4x Hsco13 Near Windy Scord
H.subscoticum P.D.Sell Oreadea 2n=27 3x Hsubs15 Ronas Voe
H.gothicoides Pugsley Tridentata 2n=37 4x Hgot07 Lunning
H.lissolepium Roffey Tridentata 2n=36 4x Hlis10 Eric’s Ham, Yell
H.umbellatum _ 2n=18 2x Humbi19 Sw/71.50
Samples supplied by Richard Gornall, Botanic Garden, University Leicester

48. HieraceumBarcoding
Chloroplast Matk geneITS of the 45S rDNA
Rubar Salih, Richard Gornall and Pat Heslop-Harrison

49. H. vinicaule H17 (2n=3x= 27)
Genomic in situ
hybridization with
Hieracium umbellatum
DNA
H. northroense H11 (2n=3x= 27)
Rubar Salih and Pat Heslop-Harrison 2014

50. FISH with rDNA probes
3x species have 3 or 6 sites
4x species have 4 or 8 sites
H. vinicaule H17 (2n=3x= 27) H. amaurostictum H1 (2n=4x= 36)
45S rDNA
45S rDNA
5S rDNA
Rubar Salih and Pat Heslop-Harrison 2014

51. K. Richert Poeggeler and Schwarzacher
Diploid hybrid
2n=14
Petunia is a
model for
DNA
transposon
work
P. hybrida
Petunia inflata X P. axillaris
2n=14 x 2n=14

52. 1. Transposon insertion, blocks the colour
production in the floral pigment pathway
2. Spontaneous excision of elements
restores colour and causes variegation
Extremely active endogenous dTph1 transposon system
Gerats, A.G., Huits, H., Vrijlandt, E., Marana, C., Souer, E., and Beld, M. (1990). Molecular
characterization of a nonautonomous transposable element (dTph1) of petunia. Plant Cell
2, 1121-1128. http://solgenomics.net/community/feature/200601.pl

53. Petunia Leader Cris Kuhlemeier with Quattrocchio, Sims, Mueller, Schranz,
Bombarely,Richert-Pöggeler, Schwarzacher, Heslop-Harrison et al.
P. inflata P. hybrida P.axillaris
http://flower.ens-lyon.fr/PetuniaPlatform/Petunia_as_a_model.html

54. Solanaceae phylogeny
Tomato Potato Tobacco
Eric Schranz and Trude Schwarzacher 2015 adapted from
Sarkinen, T., Bohs, L., Olmstead, R.G., and Knapp, S. (2013). A phylogenetic framework
for evolutionary study of the nightshades (Solanaceae): a dated 1000-tip tree.
BMC evolutionary biology 13, 214.

55. Repetitive DNA component in Petunia
Petunia Consortium 2015

56. Organelle sequences
from chloroplasts or
mitochondria
Sequences from viruses,
Agrobacterium or other
vectors
Transgenes introduced
with molecular biology
methods
Genes, regulatory and non-
coding single copy sequences
Dispersed repeats:
Transposable Elements
Repetitive DNA sequences
Plant Nuclear
Genome
Tandem repeats
DNA transposons
copied and
moved via DNA
Retrotransposons
amplifying via an
RNA intermediate
Centromeric
repeats
Structural
components of
chromosomes
Telomeric
repeats
Simple sequence
repeats or
microsatellites
Repeated genes
Subtelomeric
repeats
45S and 5S
rRNA genes
Blocks of tandem
repeats at discrete
chromosomal loci
DNA sequence components of the plant nuclear genome
Heslop-Harrison & Schmidt 2012. Encyclopedia of Life Sciences
Other genes
Horizontal DNA transfer

57. Petunia Vein Clearing
Virus (PVCV, 7206bp)
Richert-Poeggeler and Shepherd 1997
Virology 236, 137-146
Para-retrovirus
Does not need genomic integration for
replication

58. PVCV
ePVCV
metaviridae-like sequencesPVCV
integrase +2
pol +3
gag-pol +2
l clone3 (8 kb)
+2
metaviridae-like sequences
PVCV (nt 665-6153) +3gag-pol -1
+1
l clone 4 (11.4 kb)
K. Richert Poeggeler, J. Baily and Schwarzacher
Metaviridae
PVCV: Petunia vein clearing virus
ePVCV are present and are clustered with Ty3-gypsy-like sequences
Richert-Pöggeler, K.R., Noreen,
F., Schwarzacher, T., Harper, G.
and Hohn, T. (2003) Induction of
infectious Petunia vein clearing
(pararetro) virus from
endogenous provirus in petunia.
EMBO Journal 22: 4836-4845

59. PVCV
K. Richert Poeggeler and Schwarzacher
2000YA

60. methylated DNA
unmethylated DNA
non-activatable copies
(regulatory)
siRNAs
(21-25 nt)
Low level
transcripts
PTGS
non-activatable copies
(silent )
activatable copies
(potentially infectious)
Defense against
episomal virus
Defense against
episomal virus
Epigenetic
modifications
viral
suppressor?
terminal
redundant
transcripts
Transcript level sufficient
for activation and
suppressor production
Epigenetic
modifications Epigenetic
modifications
TGS
more transcripts
Weakening of
epigenetic control
Virus replication
Cell-to-cell spread
Symptoms of infection
Staginnus C, Richert-Pöggeler KR (2006).
Endogenous pararetroviruses: two-faced travelers
in the plant genome. Trends Plant Sci 11: 485-491.
PVCV may be induced by applying abiotic stress, leading to the development of
viral symptoms and increased transcript and siRNA levels.

61. Molecular cytogenetics lab
Niaz Ali
Pat Heslop-
Harrisonts32 @le.ac.uk
www.molcyt.com
UserID/PW ‘visitor’
@Pathh1
Rubar Salih
Katja
Richert-
Poeggeler
Richard Gornall

62. Thomas
Cremer
From cell theory to
chromosome
theory
Scientific realization
and theory
alterations in early
cell and heredity
research
1985

63.  Mendel’s life
 Mendel’s experiments
 Why was he forgotten?
 What was known about chromosomes
at the time of Mendel
 Mendel’s rediscovery
 How has chromosome biology
developed since
 Some examples from our own research
Overview

64. 150th anniversary
Versuche über
Pflanzenhybriden
(Experiments with
plant hybrids)
1865
Gregor Mendel
(1822-1884)