The return of Cytogenetics

Meadowfoam meiosis Metaphase I Anaphase I n n 2n Reduction division

Meadowfoam meiosis Metaphase I Anaphase I a A a A Mendel’s first law – law of segregation

Meadowfoam meiosis Metaphase I Anaphase I a B a B A b A b

Meadowfoam meiosis Metaphase I Anaphase I a B a b A B A b Mendel’s second law – law of independent assortment

But what if the genes are on the same chromosome? Metaphase I Anaphase I a B a b A B A b

But what if the genes are on the same chromosome? Metaphase I Anaphase I a B a b A B A b No independent assortment Deviation from Mendel’s second law

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 Anaphase I n - 1 n + 1

Wheat Monosomic

R.J. Singh 2002 Barley trisomic 6

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 a a geneexpression

Set of deletion lines location of gene A A A a a a geneexpression

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

Disomic Nulli 1ANulli 1BNulli 1D Southern blot results with marker used as a probe – what is the chromosome location of the probe?

Disomic Nulli 1ANulli 1BNulli 1D Southern blot results with marker used as a probe – probe is on chromosome 1D

Disomic Nulli 1ANulli 1BNulli 1D Telo 1DSTelo 1DL Southern blot results with marker used as a probe – what is the chromosome arm location of the probe?

Disomic Nulli 1ANulli 1BNulli 1D Telo 1DSTelo 1DL Southern blot results with marker used as a probe – Chromosome arm location – 1DS

Disomic Nulli 1ANulli 1BNulli 1D Telo 1DSTelo 1DL Del 1DS-1Del 1DS-2Del 1DS-3 Southern blot results with marker used as a probe – what section of chromosome IDS is the location of the probe?

Disomic Nulli 1ANulli 1BNulli 1D Telo 1DSTelo 1DL Del 1DS-1Del 1DS-2Del 1DS-3 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

21 st century Cytogenetics - molecular cytogenetics

In situ hybridization Canola / Rapeseed

Visualization of C genome chromosomes BC 1 between wheat and jointed goatgrass - which species is the recurrent parent?

Count number of yellow chromosomes, greater than 7 – recurrent parent jointed goatgrass BC 1 between wheat and jointed goatgrass - which species is the recurrent parent?

Maize chromosomes