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Chp-7

Dr. Syed Mohammed Ahmad ; Rehana Khan Laxmi Publications PDF

CHROMOSOMES

AND

DISEASE

Chapt er

Chapter

CHROMOSOMES

AND

191

7

DISEASE

INTRODUCTION

The congenital malformation called mongolism affects one in approximately 650. Ever since the condition was identified in the 1860’s by the British neurologist John Langdon Down, concerned physicians and investigators had been seeking its cause. For many years, Mongolism was described as a heredity disease, the result of some unknown effects in the “germplasm”.

Investigators dissatisfied with such vague explanations have argued the opposite view that the disease is environmental, and have correlated its incidence with accidents due to the developing embryo during gestation, that is, the period between conception and birth.

The explanation of mongolism is now at hand. The disease is neither typically hereditary nor environmental, as these terms are commonly employed. It arises from a defect in the mechanism by which the heredity material is passed on from parent to offspring. This leaves certain questions unanswered: for example, whether the defect in the genetic mechanism is itself hereditary or environmental in origin. The explanation is nonetheless of great significance, for it is among the first findings to come from direct investigation of the genetic apparatus of the human cell. The techniques of cell genetics have mostly been restricted to more easily studied cells of lower animals and plants.

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Weathering: GED Earth Science

Ace Academics Ace Academics ePub
Medium 9780253356758

9 The Late Carboniferous: Expanding Horizons

Jennifer A. Clack Indiana University Press ePub

9.1. Drawings of Late Carboniferous plants. (A) Sigillaria sp., a lycopsid (club moss) with a trunk up to 1 meter in diameter. (B) Psaronius sp., a tree fern related to the modern family Marattiales. (C) Callistophyton sp., a trailing pteridosperm. (D) Lepidodendron sp., a lycopsid (club moss) up to 54 meters high. (E) Calamites carinatus, a horsetail (Equisetales). (F) A member of the Cordaites family, a gymnosperm with trunk diameter up to 1 meter.

Late Carboniferous/Early Permian Biogeography and Paleoecology

During the Late Carboniferous, the continents, which had slowly moved southward through the Devonian and Early Carboniferous, changed direction and began to rotate. Gondwana and Euramerica gradually collided, initiating the formation of the supercontinent Pangaea. The world’s vegetation had differentiated into continental regions so that, for example, the Gondwana flora became quite distinct from those of Euramerica and of what are now China and Siberia. At this time, Euramerica, positioned in the tropics, was covered by a vast swamp forest, while to the north and south of it, evaporite deposits speak of arid climates (Milner 1993a).

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3: Risk Assessment

Wapling, A. CABI PDF

3 

Risk Assessment

J. Bush

Corporate Risk Manager, Waitemata District Health Board, New Zealand

Key Questions 

What is a risk?

How are risks assessed and quantified in relation to emergency preparedness?

What decisions are available once the risk has been quantified?

How does risk information influence the emergency preparedness work plan?

3.1  What is Risk and Risk Management?

There are many variations of the definition of risk; however, they all have a common theme to them, which is that risk is measured in terms of consequence (impact) and likelihood (chance/probability) of an event occurring.

Risk can be described as the uncertainty of outcome, be it positive (an opportunity) or negative (a threat), if an event occurs.

Once there is an understanding of what risk is, there is a need to understand what risk management is and why it should be done. Risk management is not a dark art; it is something everyone does in both work and personal lives, often without realizing it (e.g. the continual risk-based decision making that takes place when travelling to work). Individuals make judgements about risks, actions and safety, and decide on the level of risk they (or the organization) is willing to accept for a perceived gain. Risk management is the process that enables an organization to: understand what risks it faces; understand what events or hazards might cause harm to individuals or the organization; assess the risk; and identify existing and/or additional controls that are needed to either prevent the risk event(s) or mitigate the impact should the risk event(s) materialize.

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5 The Descriptive Embryology of Male and Female Development

Elof Axel Carlson Indiana University Press ePub

The study of embryology was extremely limited until the 1860s, when several techniques came together. One was the development of achromatic lenses, which allowed scientists to observe cells or other small objects without the confusion of chromatic aberration and spherical aberration. Chromatic aberration involves the breaking up of white light into a rainbow of concentric colors around an object. Spherical aberration is even worse because there is no central focus and competing points of convergence lead to a blurred image. Joseph Jackson Lister (1786–1869), whose more famous son, Joseph Lister (1827–1912), introduced antiseptic surgery, provided the solution.1

Like his father, Lister was a wine merchant. They were Quakers and fairly pious. Lister worked after hours on his interest in natural history. When he took up microscopy, he found the interference with sharp images annoying and switched to making his own lenses. Lister found that dissolving lead and other salts into glass changed the density within these glasses, which yielded different focal lengths when he made lenses from them. He eventually worked out a combination of two layers of molten glass (crown glass and flint glass), one correcting the other for both chromatic and spherical aberration. The resulting achromatic lenses revolutionized both astronomy (allowing bigger telescopic lenses) and biology (allowing compound microscopes that would multiply an object up to 2000 times. He began his experiments on lenses in 1824 and found a suitable achromatic lens in 1826, which he refined until publishing his findings in 1830.

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