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 …
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 …
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 …
Introduction to Microbiology
Microorganisms are defined as those organisms and acellular biological entities too small to be seen clearly by the naked eye They are generally 1 millimeter or less in diameter. …
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: Males are affected …
PEDIGREE ANALYSIS OF AUTOSOMAL DOMINANT DISORDERS
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 …
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 …
Epistasis
It is the type of gene interaction in which one gene locus masks or modifies the phenotype of other gene locus In trying to find evidence of gene interaction, …
Recessive Lethal Alleles
Many mutant alleles are capable of causing the death of an organism; such alleles are called lethal alleles. The human disease alleles provide examples. A gene whose mutations may …
Carbon Cycle
Carbon is the element that defines life, and as such it is everywhere. The exchange of elements between sources and sinks is referred to as flux. Carbon is present …