Shape, Arrangement, and Size

It might be expected that bacterial cells, being small and relatively simple, would be uniform in shape and size. This is not the case, as the microbial world offers considerable variety in terms of morphology. However, the two most common …

Major Fields in Microbiology

Pathogenic microbes, though relatively few in number, have had and continue to have considerable impact on humans. Thus one of the most active and important fields in microbiology is medical microbiology, which deals with diseases of humans and animals. Medical …

Microorganisms and Disease

Although Fracastoro and a few others had suggested that invisible organisms produced disease, most people believed that disease was caused by supernatural forces, poisonous vapors called miasmas, and imbalances among the four humors thought to be present in the body. …

Microscopy and the Discovery of Microorganisms

The earliest microscopic observations of organisms appear to have been made between 1625 and 1630 on bees and weevils by the Italian Francesco Stelluti (1577-1652), using a microscope probably supplied by Galileo (1564-1642). Robert Hooke (1635-1703) is credited with publishing …

Introduction

Microorganisms are defined as those organisms and acellular biological entities too small to be seen clearly by the unaided eye They are generally 1 millimeter or less in diameter. Although small size is an important characteristic of microbes, it alone …

X-linked recessive disorders

Let’s look at the pedigrees of disorders caused by rare recessive alleles of genes located on the X chromosome. Such pedigrees typically show the following features: 1. Many more males than females show the rare phenotype under study. The reason …

Autosomal inheritance in humans

Human matings, like those of experimental organisms, show many examples of the inheritance patterns described above. Because controlled experimental crosses cannot be made with humans, geneticists must resort to scrutinizing records in the hope that informative matings have been made …

Penetrance and expressivity

Many mutations show incomplete penetrance: not every individual with the genotype expresses the corresponding phenotype. Thus penetrance is defined as the percentage of individuals with a given allele who exhibit the phenotype associated wit many mutations show incomplete penetrance: not …