Complete Dominance Definition Complete dominance occurs when one allele – or “version” – of a gene completely masks another. The trait that is expressed is described as being “dominant” over the trait that is not expressed. Most organisms are diploid – that is, they get two copies of each gene, one from each of their … Read more

Zoology Definition Zoology, or animal biology, is the field of biology that involves the study of animals. The word zoology comes from the Greek words zōion, meaning “animal”, and logos, meaning “the study of”. It encompasses all aspects of scientific knowledge about animals, like embryonic development, evolution, behavior, ecological distribution, and classification.  Zoology is broken … Read more

Oviparous Definition An oviparous animal is one that produces eggs, and the young hatch after being expelled from the body. While fertilization of the egg can occur internally or externally, oviparous animals always hatch their young outside of their body.  Many amphibians, birds, fish and reptiles are oviparous and often make nests to protect their … Read more

Commensalism Definition Commensalism is a relationship between two organisms in which one organism benefits, and one is unaffected. This can be contrasted with other types of symbiosis, such as mutualism and parasitism. The supposed difference between commensalism and other types of symbiosis is that in commensalism, the second party or host remains unaffected.  Some scientist … Read more

Incomplete Dominance Definition Incomplete dominance is when a dominant allele, or form of a gene, does not completely mask the effects of a recessive allele, and the organism’s resulting physical appearance shows a blending of both alleles. It is also called semi-dominance or partial dominance. One example is shown in roses.  The allele for red … Read more

Primary Consumer Definition A primary consumer is an organism that feeds on primary producers. Organisms of this type make up the second trophic level and are consumed or predated by secondary consumers, tertiary consumers or apex predators. Primary consumers are usually herbivores that feed on autotrophic plants, which produce their own food through photosynthesis. Several … Read more

The Route of the Human Midsagittal Plane Generally, the midsagittal plane depicts the human in anatomical position with arms and legs slightly apart, as shown here. Left and right midsagittal sections are referred to as left and right sides of the subject, not to the point of view of the person looking at, for example, … Read more

Operator Definition An operator is a genetic sequence which allows proteins responsible for transcription to attach to the DNA sequence. The gene, or genes, which get transcribed when the operator is bound are known as the operon.  Repressor proteins, which bind to the gene operator, can block transcription factors from binding to the operator. The … Read more

A diploid cell contains two complete sets of chromosomes in its nucleus, whereas haploid cells only contain a single copy. Most human body cells are diploid, and only the gametes (sperm and egg cells) are haploid. Chromosomes in diploid cells are arranged in homologous pairs. The diploid chromosome number of a cell (2n) is the … Read more