Interaction of Genes

The phenotypic ratios obtained by Mendel in garden peas demonstrate that one gene controls one character; of the two alleles of a gene, one allele is completely dominant over the other. Due to this the heterozygote has a phenotype identical to the homozygous parent. Soon after Mendel’s work was rediscovered, instances came to light where a gene was not producing an individual effect. On the contrary, genes were interacting with each other to produce novel phenotypes which did not exhibit dominance relationships observed in Mendel’s experiments. In one of the first cases reported by Kölreuter, the heterozygote showed a phenotype intermediate between the parental phenotypes. This was termed incomplete dominance or intermediate inheritance. 

BLOOD GROUP SYSTEMS

In 1901 scientists discovered the fi rst blood groups— those of the ABO system. Since then, the realization that red blood cells possess proteins that can be used to classify them into various blood groups has revolutionized medicine. Prior to this knowledge, blood transfusions were dangerous and had unpredictable outcomes, with some patients experiencing severe reactions and others faring well for unknown reasons. Today, however, because blood group proteins on red cells can be identified accurately and because donor blood is screened for the presence of potentially dangerous infectious organisms, blood transfusions are relatively safe and effective

Ecology and its Domain

The word ‘ecology’ was first used by Ernest Haeckel in 1869. Paraphrasing Haeckel we can describe ecology as the scientific study of the interactions between organisms and their environment. The word is derived from the Greek oikos, meaning ‘home’. Ecology might therefore be thought of as the study of the ‘home life’ of living organisms. A less vague definition was suggested by Krebs (1972): ‘Ecology is the scientific study of the interactions that determine the distribution and abundance of organisms’. Notice that Krebs’ definition does not use the word ‘environment’; to see why, it is necessary to define the word. The environment of an organism consists of all those factors and phenomena outside the organism that influence it, whether these are physical and chemical (abiotic) or other organisms (biotic).