B chromosomes are associated with redistribution of genetic recombination towards lower recombination chromosomal regions in perennial ryegrass.

Supernumerary 'B' chromosomes are non-essential components of the genome present in a range of plant and animal species-including many grasses. Within diploid and polyploid ryegrass and fescue species, including the forage grass perennial ryegrass (Lolium perenne L.), the presence of B chromosomes has been reported as influencing both chromosome pairing and chiasma frequencies. In this study, the effects of the presence/absence of B chromosomes on genetic recombination has been investigated through generating DArT (Diversity Arrays Technology) marker genetic maps for six perennial ryegrass diploid populations, the pollen parents of which contained either two B or zero B chromosomes. Through genetic and cytological analyses of these progeny and their parents, we have identified that, while overall cytological estimates of chiasma frequencies were significantly lower in pollen mother cells with two B chromosomes as compared with zero B chromosomes, the recombination frequencies within some marker intervals were actually increased, particularly for marker intervals in lower recombination regions of chromosomes, namely pericentromeric regions. Thus, in perennial ryegrass, the presence of two B chromosomes redistributed patterns of meiotic recombination in pollen mother cells in ways which could increase the range of allelic variation available to plant breeders.

Cranial Treatment and Spinal Manipulation for a Patient With Low Back Pain: A Case Study.

OBJECTIVE: The purpose of this case study is to present chiropractic management of a patient with chronic low back pain by focusing on the craniomandibular system. CLINICAL FEATURES: A 37-year-old man consulted a chiropractor for pain in the lumbosacral area with radiation down the anterolateral side of the upper left leg. The symptoms started after a fall the previous year. Examination showed a post-traumatic chronic L4-L5 facet dysfunction and left sacro-iliac joint dysfunction. Chiropractic spinal manipulation to the lumbar spine and pelvis gave only temporary relief from the pain. INTERVENTION AND OUTCOME: A year later a bone scintigraphy was conducted, in which a lesion was found over the right sphenoid area. Cranial treatment of this area was added to the chiropractic treatment plan. After this treatment, the patient reported that he was pain free and could return to normal activities of daily living. CONCLUSION: The clinical progress of this case suggests that for some patients, adding craniosacral therapy may be helpful in patients with low back symptoms.