The Language of Genetics
Gene – A segment of DNA whose sequence of nucleotides specifies the sequences of
amino acids for a particular protein. “The blueprint” instructions coding for a given
protein. Alternatively a unit of hereditary material located on a chromosome that, by
itself or with other genes, determines a characteristic in an organism.
Genotype – An individuals genetic makeup. That is the combination of alleles carried by
an organism for a given trait(s).
Phenotype – Physical characteristics expressed by an individual – dependent upon the
genotype. Can include characteristics of:
- outward appearance
- molecular expression e.g. blood type
- behavior
Allele – Alternate form of a gene on the same locus. Produced when there are
differences in nucleotide sequences at the same gene locus. New variations occur due to
mutations i.e. changes in DNA sequence.
Locus – A gene’s specific physical location on a chromosome.
Dominant – An allele that can determine the phenotype, even in the heterozygote
condition.
Recessive – An allele that can determine the phenotype only when in the homozygous
condition.
Chromosomes – A package of DNA and its associated histones, seen only during
cellular division i.e. mitosis or meiosis. They stain dark and are usually rod shaped.
Homologous Chromosomes – Chromosomes containing the same genes coding for
specific traits. A pair of chromosomes, one from female parent, and one from male
parent in a diploid cell.
Homozygous -When two homologous chromosomes carry the SAME alleles at a given locus.
Heterozygous – When two homologous chromosome carry DIFFERENT alleles at a
given locus. Generally the “dominant” allele is what
will be expressed.
Codominance – The relation between two alleles of a gene, such that BOTH alleles are
phenotypically expressed e.g. AB blood type.
Incomplete dominance – A pattern of inheritance where in the heterozygote condition
the phenotype is intermediate between the two phenotypes i.e. blended result.