Genes and Heredity



Heredity is the inheritance of traits by offspring from their parents through a transfer of genetic material. Genes are stored in the deoxyribonucleic acid (DNA) within the chromosomes of every cell. These genes dictate the cellular functions of microorganisms. Transcription is the process of creating a complementary messenger ribonucleic acid (mRNA) strand from a DNA template. Translation is the production of protein from the mRNA transcript. Gene expression in bacteria is controlled by operons, where a single promoter controls several genes. Bacteria are capable of both vertical and horizontal gene transfer. Viral transcription and translation processes vary depending on the viral type (RNA or DNA virus). Archaea replicate their circular genome similar to bacteria but share transcription and translation factors with eukaryotic organisms. Genetic mutations, or changes in the genes, affect prokaryotes and eukaryotes alike. Mutations affect the genotype, or genetic code, and this may cause changes to the phenotype, or external appearance, of an organism.

At A Glance

  • Genetics is the study of trait inheritance. A gene is the site on the chromosome that provides the DNA information for a particular trait. The genome is the sum of total genetic material.
  • DNA is composed of three main parts: deoxyribose, a phosphate group, and a nitrogen base. The DNA of cellular organisms takes the form of a double helix, where each strand of DNA joins another by connecting nitrogen bases.
  • Packaging of DNA differs between prokaryotes and eukaryotes. Eukaryotes can have multiple chromosomes inside a membrane-bound nucleus. Prokaryotes have a single chromosome called a genophore packaged in an area called a nucleoid.
  • Bacterial DNA replication is accomplished by unwinding the double helix so that new DNA can be assembled by DNA polymerase. This newly synthesized strand is called the daughter strand.
  • DNA templates are transcribed into complementary mRNA strands, which are translated into proteins.
  • Collections of genes in bacteria that code for products with a coordinated function are operons. Genetic regulation of protein synthesis relies on operons—some are inducible and some are repressible.
  • All organisms can acquire new genes not directly inherited from a parent through gene transfer. In bacteria, this is completed by one of the three types of horizontal gene transfer: transformation, transduction, and conjugation.
  • Mutations cause changes in the genome that can impact the phenotype in a positive, negative, or neutral way. They occur as point mutations or frameshift mutations and can be randomly introduced (spontaneous) or induced by exposure to a mutagen.