Download Slide 1 - Barley World

The return of Cytogenetics
Meadowfoam meiosis
2n
n
n
Metaphase I
Anaphase I
Reduction division
Meadowfoam meiosis
A
a
a
A
Metaphase I
Anaphase I
Mendel’s first law – law of segregation
Meadowfoam meiosis
B
A
a
b
B
Metaphase I
a
b
A
Anaphase I
Meadowfoam meiosis
b
A
a
b
B
Metaphase I
a
B
A
Anaphase I
Mendel’s second law – law of independent assortment
But what if the genes are on the same chromosome?
A
b
aB
Metaphase I
Ba
bA
Anaphase I
But what if the genes are on the same chromosome?
A
b
aB
Ba
bA
Anaphase I
Metaphase I
No independent assortment
Deviation from Mendel’s second law
Creating gene maps
Creating gene maps
Many genes were mapped to specific
chromosomes and specific chromosome arms
in wheat and barley before the advent of
molecular genetics
How was this possible?
Chromosome mapping
Many genes were mapped to specific
chromosomes in wheat and barley before the
advent of molecular genetics
How was this possible?
Deviation from Mendel’s laws
Chromosome mapping
- Monosomics
- Trisomics
- Deletions
Metaphase I
non-disjunction
n-1
Anaphase I
n+1
Wheat Monosomic
Barley trisomic 6
R.J. Singh 2002
Barley telotrisomic 6S
If there is a chromosome or part of a chromosome
missing the inheritance of any gene on the missing
part will deviate from Mendel’s laws
If there is an extra chromosome or chromosome arm
the inheritance of any gene on the extra chromosome
will also deviate from Mendel’s laws
Combining cytogenetics and molecular genetics for
gene mapping
Wheat deletion series – mapping wheat gene
locations
Wheat is a hexaploid with 3 genomes A, B and D.
The genes are arranged on the same chromosomes in
the different genomes, making the chromosomes
homeologous (1A, 1B and 1D carry similar genes)
Set of deletion lines
A
A A a
gene expression
a
a
Set of deletion lines
location of gene
A
A A a
gene expression
a
a
How do you know which chromosome to test?
- Screen plants that carry 4 copies of one
chromosome and no copies of a homeologous
chromosome (nulli-tetrasomic)
Example: nulli-tetrasomic for chromosome 1D
0 copies of chromosome 1D, 4 copies of
either chromosome 1A or chromosome 1B
Nulli 1D
Nulli 1B
Nulli 1A
Disomic
Southern blot results with marker used as a
probe – what is the chromosome location of the
probe?
Nulli 1D
Nulli 1B
Nulli 1A
Disomic
Southern blot results with marker used as a
probe – probe is on chromosome 1D
Telo 1DL
Telo 1DS
Nulli 1D
Nulli 1B
Nulli 1A
Disomic
Southern blot results with marker used as a probe –
what is the chromosome arm location of the probe?
Telo 1DL
Telo 1DS
Nulli 1D
Nulli 1B
Nulli 1A
Disomic
Southern blot results with marker used as a probe –
Chromosome arm location – 1DS
Del 1DS-3
Del 1DS-2
Del 1DS-1
Telo 1DL
Telo 1DS
Nulli 1D
Nulli 1B
Nulli 1A
Disomic
Southern blot results with marker used as a
probe – what section of chromosome IDS is the
location of the probe?
Del 1DS-3
Del 1DS-2
Del 1DS-1
Telo 1DL
Telo 1DS
Nulli 1D
Nulli 1B
Nulli 1A
Disomic
Gene is on the short arm of chromosome
1D in the region covered by deletion 1DS-3
Genome sequencing
- Barley
How can you separate out a specific
chromosome for sequencing?
Genome sequencing
- Barley
How can you separate out a specific
chromosome for sequencing?
Use differences in chromosome size
provided by the presence of
telochromosomes in telo-trisomics
Barley telotrisomic 6S
Transposable elements
Barbara McClintock
- cytogeneticist
- worked on corn
- in the 1940’s worked on a trait that
appeared to change locations on a
chromosome (inversions) and/or move
between chromosomes (translocations)
- problem, no observable chromosome
changes
- so she proposed the idea of transposable
elements
21st century Cytogenetics
- molecular cytogenetics
In situ hybridization
Canola / Rapeseed
BC1 between wheat and jointed goatgrass
- which species is the recurrent parent?
Visualization of C genome chromosomes
BC1 between wheat and jointed goatgrass
- which species is the recurrent parent?
Count number of yellow chromosomes, greater
than 7 – recurrent parent jointed goatgrass
Maize chromosomes