**Tomás Naranjo**

*Review*

Departamento de Genética, Fisiología y Microbiología, Facultad de Biología, Universidad Complutense de Madrid, 28040 Madrid, Spain; toranjo@bio.ucm.es; Tel.: +34-913945040

Received: 23 August 2019; Accepted: 11 September 2019; Published: 14 September 2019

**Abstract:** The tribe *Triticeae* contains about 500 diploid and polyploid taxa, among which are important crops, such as wheat, barley and rye. The phylogenetic relationships, genome compo-sition and chromosomal architecture, were already reported in the pioneer genetic studies on these species, given their implications in breeding-related programs. Hexaploid wheat, driven by its high capacity to develop cytogenetic stocks, has always been at the forefront of these studies. Cytogenetic stocks have been widely used in the identification of homoeologous relationships between the chromosomes of wheat and related species, which has provided valuable information on genome evolution with implications in the transfer of useful agronomical traits into crops. Meiotic recombination is non-randomly distributed in the *Triticeae* species, and crossovers are formed in the distal half of the chromosomes. Also of interest for crops improvement is the possibility of being able to modulate the intraspecific and interspecific recombination landscape to increase its frequency in crossover-poor regions. Structural changes may help in this task. In fact, chromosome truncation increases the recombination frequency in the adjacent intercalary region. However, structural changes also have a negative effect upon recombination. Gross chromosome rearrangements produced in the evolution usually suppress meiotic recombination between non-syntenic homoeologs. Thus, the chromosome structural organization of related genomes is of grea<sup>t</sup> interest in designing strategies of the introgression of useful genes into crops.

**Keywords:** chromosome rearrangements; meiotic recombination; crossover distribution; *Triticeae*; wheat; barley; rye
