4.1. Genetics terms

  • 16678458-abstract-word-cloud-for-genetics-with-related-tags-and-termsGene. Units of inheritance usually occurring at specific locations, or loci, on a chromosome.  Physically, a gene is a sequence of DNA bases that specify the order of amino acids in an entire protein or, in some cases, a portion of a protein.  A gene may be made up of hundreds of thousands of DNA bases.  Genes are responsible for the hereditary traits in plants and animals.
  • Allele. alternate forms or varieties of a gene. The alleles for a trait occupy the same locus or position on homologous chromosomes and thus govern the same trait.  However, because they are different, their action may result in different expressions of that trait.
  • Genome. The full genetic complement of an individual (or of a species).  In humans, it is estimated that each individual possesses approximately 2,9 billion base units in his or her DNA.
  • Dominant allele. An allele that masks the presence of a recessive allele in the phenotype.   Dominant alleles for a trait are usually expressed if an individual is homozygous dominant or heterozygous.
  • Recessive allele. An allele that is masked in the phenotype by the presence of a dominant allele.  Recessive alleles are expressed in the phenotype when the genotype is homozygous recessive (aa).
  • Codominant inheritance. The situation in which two different alleles for a trait are expressed unblended in the phenotype of heterozygous individuals.  Neither allele is dominant or recessive, so that both appear in the phenotype or influence it.  The colour of the flowers of Mirabilis jalapa (The four o’clock flower or marvel of Peru). Some of them are red, another white, and if you cross them the result are pink flowers.
  • Genotype. the genetic makeup of an individual.  Genotype can refer to an organism’s entire genetic makeup or the alleles at a particular locus.  See phenotype.
  • Phenotype. the observable or detectable characteristics of an individual organism–the detectable expression of a genotype.

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