Hexaploid wheat- Triticum aestivum 2n= 6x= 42 1234567 A B D abcdabcd abcdabcd abcdabcd Very large chromosomes with similar gene orders 7A abcdabcd Homoeologues.

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Hexaploid wheat- Triticum aestivum 2n= 6x= A B D abcdabcd abcdabcd abcdabcd Similar gene orders but different content of similar repeats 7A.

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Hexaploid wheat- Triticum aestivum 2n= 6x= A B D abcdabcd abcdabcd abcdabcd Very large chromosomes with similar gene orders 7A abcdabcd Homoeologues abcdabcd 7B abcdabcd 7D The Ph1 locus (a dominant locus) restricts pairing to homologues Riley and Chapman (1958) Nature The Ph1 locus stabilises wheat, ensuring high fertility

Importance of Ph1 in Breeding Wheat-rye hybrid Ph1+ Ph1- Ph1 stops wheat and wild species chromosomes pairing A single wheat carrying a deletion of Ph1 locus (ph1b- 70Mb in size) used in breeding- is heavily rearranged Can we from understanding Ph1 locus, temporary switch Ph1 off in hybrids of elite wheat varieties crossed with wild species? Wild species of wheat carry important traits for disease resistance, salt, cold and drought tolerance

AA Bb b aa B homologueshomoeologues Different expression patterns Homologues and homoeologues replicated at different times as remodelling is slowed- thus will be in different conformations for meiosis All chromosomes replicated together Homoeologues remodelled together Homologues premature remodelling Ph1 + Cdk2 rate limiting remodelling slows Ph1+ Ph1- Ph1 story Ph1 locus is a Cdk2-like gene complex Cdk2 in humans remodels chromatin for replication Ph1- Cdk2 Abundant

Drug strategy- needle in haystack? How do you activate cdk? Inhibit phosphatases which deactivate cdks- increase cdk activity? Phosphatase inhibitors cause premature condensation and rapid progression through meiotic prophase I in humans and mouse

Can we inhibit phosphatases to modulate pairing in hybrids? Can we improve the exploitation the introgression process? Application? Ph1+ Wheat x rye hybrid