Genetics and competing strategies in a threshold model for mail processing

Multi-agent algorithms inspired by the division of labour in social insects are applied to a problem of distributed mail retrieval in which agents must visit mail producing cities and choose between mail types under certain constraints.The efficiency (i.e. the average amount of mail retrieved per time step), and the flexibility (i.e. the capability of the agents to react to changes in the environment) are investigated both in static and dynamic environments. New rules for mail selection and specialisation are introduced and are shown to exhibit improved efficiency and flexibility compared to existing ones. We employ a genetic algorithm which allows the various rules to evolve and compete. Apart from obtaining optimised parameters for the various rules for any environment, we also observe extinction and speciation. From a more theoretical point of view, in order to avoid finite size effects, most results are obtained for large population sizes. However, we do analyse the influence of population size on the performance. Furthermore, we critically analyse the causes of efficiency loss, derive the exact dynamics of the model in the large system limit under certain conditions, derive theoretical upper bounds for the efficiency, and compare these with the experimental results.

The visual complications of Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disorder affecting middle-aged and elderly people. The disorder is of particular interest to Optometrists because it is associated with a range of visual problems including defects in eye movement and pupillary function. This article reviews the visual complications of PD and the pathological changes in the eye and brain which may explain these symptoms.

Retinoblastoma and the new genetics

Wardop first described retinoblastoma in 1809. It is the most common intraocular tumour of childhood and the most common tumour of the retina. It was originally thought to be a glioma arising from glial cells of the retina. However, in 1926 it was recognised as a tumour of undifferentiated photoreceptor cells. This article describes the basic clinical and pathological aspects of retinoblastoma, the advances in molecular genetics which have led to the discovery of the gene responsible, and the defects which have been discovered in the retinoblastoma gene.

Retinitis pigmentosa and the new genetics

This article describes the recent advances that have been made in understanding the molecular genetics of retinitis pigmentosa (RP). The basic clinical and pathological aspects of RP will be described, together with the patterns of inheritance exhibited by the disorder. In addition, the most important genes that have been linked to RP will be discussed as well as the advances in molecular genetics which have led to the identification of mutations in these genes.

The genetics of cataract

This article reviews: 1) the clinical and pathological features of the different types of catarct, 2) the patterns of inheritance of cataract, 3) the genes that may be associated with the development of cataract, and 4) how the presence of abnormal genes may cause lens opacity.

The genetics of glaucoma

The present article reviews the patterns of inheritance associated with glaucoma, how the genes linked to the disease have been located and identified, and considers how the effect of some of these genes could lead to glaucoma.

Genetics of optic atrophy: recent progress in understanding

This article considers the clinical symptoms associated with hereditary optic atrophy and reviews recent progress in our understanding the genetics of the disorder. The major genes linked to optic atrophy are identified and how defects in these genes could lead to the optic disc pathology is discussed.