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 …
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 …
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. …
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 …
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 …
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 …
Most animals and many plants show sexual dimorphism; in other words, individuals are either male or female. In most of these cases, sex is determined by a special pair of sex chromosomes. Let’s look at humans as an example. Human …
What pedigree patterns are expected from autosomal dominant disorders? Here the normal allele is recessive, and the abnormal allele is dominant. It may seem paradoxical that a rare disorder can be dominant, but remember that dominance and recessiveness are simply …
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 …
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 …