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Biology - Genetics Glossary

Adenine : a purine base found in DNA and RNA.

Allele : an alternative form of a gene.

Amino acid : a unit composed of an amino group, a carboxyl group, and a radical group; amino acids link together in chains to form polypeptides.

Anaphase : a stage of cell division in mitosis when replicated chromosomes separate. In meiosis, homologous chromosomes separate during anaphase I, and replicated chromosomes separate during anaphase II.

Aneupolidy : the increase or decrease in the number of chromosomes; a deviation from an exact multiple of the haploid number of chromosomes.

Anticipation : the increasing severity or decreasing age of onset of a genetic trait or disorder with succeeding generations.

Anticodon : the three nucleotides in tRNA complementary to a corresponding codon of mRNA.

Antiparallel : parallel but running in opposite directions; orientation of two complementary strands of DNA.

Apoptosis : the normal process of regulated cell death.

Autosome : a nonsex chromosome.

Backcross : a cross between an individual with an F1 genotype and an individual with one of the parental (P) genotype.

Bacteriophage : a virus that infects bacterial cells.

Base : one of the three components of a nucleotide. Bases are found in RNA and DNA.

Cell cycle : the repeated process of cell growth, DNA replication, mitosis and cytokinesis.

Centromere : the region at the centre of a chromosomethat appears pinched during metaphase; where spindle fibres attach during mitosis and meiosis.

Chromatid : one half of a replicated chromosome

Chromosome : a linear or circular strand of DNA that contains genes.

Co-dominance : is when heterozygotes express both alleles equally.

Codon : is a combination of three nucleotides in an mRNA that correspond to an amino acid.

Complementary : specific matching of base pairs in DNA or RNA.

Crossing-over : is the equal exchange of DNA between homologous chromosomes during meiosis.

Cytokinesis : cell division.

Cytosine : a pyrimidine base found in DNA and RNA.

DNA : deoxyribonucleic acid: the molecule that carries genetic information.

dNTP : deoxyribonucleotide: the basic building block of DNA used during DNA replication consisting of a deoxyribose sugar, three phosphate molecules, and one of four nitrogenous bases.

ddNTP : dideoxyribonucleotide: identical to dNTP but lacking an oxygen at the 3’ site. Used in DNA sequencing.

Deamination : is when a base loses an amino group.

Degenerate : a property of the genetic code whereby some amino acids are encoded by more than one codon.

Deletion : a mutation resulting in the loss of one or more nucleotides from a DNA sequence.

Denaturation : melting bonds between DNA strands, thereby separating the double helix into single strands.

Depurination : is when a nucleotide loses a purine base.

Dihybrid cross : a cross between two individuals who differ at two traits or loci.

Diploid : possessing two copies of each chromosome.

Dominant : a phenotype or allele that completely masks another allele. The phenotype exhibited by both homozygotes and heterozygotes carrying a dominant allele.

Epistasis : gene interaction in which one gene hides the action of another.

Eukaryote : an organism with a complex cell structure and cell nucleus.

Euploid : an organism possessing an exact multiple of the haploid number of chromosomes.

Exon : the coding part of a gene.

Expressivity : variation in the strength or traits.

F1 generation : the first generation offspring of a specific cross.

F2 generation : the offspring of the F1 generation.

Gamete : a reproductive cell, sperm or egg cell.

Gene : a fundamental unit of heredity. A specific section of DNA within a chromosome.

Genome : a full set of chromosomes carried by a particular organism.

Genotype : the genetic makeup of an individual. The allele(s) possessed at a given locus.

Guanine : a purine base found in DNA and RNA.

Gyrase : an enzyme that acts during DNA replication to prevent tangles from forming in the DNA strand.

Haploid : possessing one copy of each chromosome.

Helicase : an enzyme that acts during DNA replication to open the double helix.

Heterozygote : an individual with two different alleles of a given gene pr locus.

Homologous chromosomes : two chromosomes that are identical in shape and structure and carry the same genes.

Homozygote : an individual with two identical alleles of a given gene or locus.

Insertion : a mutation resulting in the addition of one or more nucleotides to a DNA sequence.

Interphase : is the period of cell growth between divisions.

Intron : the non-coding part of a gene. Intervening sequences that interrupt exons.

Ligase : the enzyme that acts during DNA replication to seal gaps created by lagging synthesis.

Linkage : inheriting genes located close together on chromosomes as a unit.

Locus : is a specific location on a chromosome.

Meiosis : cell division in sexually reproducing organisms that reduces the amount of genetic information by half.

Metaphase : a stage of cell division when chromosomes align along the equator of the dividing cell.

Mitosis : is simple cell division without a reduction in chromosome number.

Nucleotide : the building block of DNA, composed of a deoxyribose sugar, a phosphate, and one of four nitrogenous bases.

P-generation : the parental generation in a genetic cross.

Pentrance : the percentage of individuals with a particular genotype that express the trait.

Phenotype : the physical characteristics of an individual.

Polypeptide : a chain of amino acids that form a protein.

Prokaryote : an organism with a simple cell structure and no cell nucleus.

Prophase : a stage of cell division when chromosomes contract and become visible and the nuclear membrane begins to break down. In meiosis, crossing-over takes place during prophase.

Purine : a compound composed of two rings.

Pyrimidine : chemicals that have a single six-sided ring structure.

RNA : ribonucleic acid, the single-stranded molecule that carries information carried by DNA to the protein-manufacturing part of the cell.

Recessive : a phenotype or allele exhibited only by homozygotes.

Replication : the process of making an exact copy of a DNA molecule.

Telomere : the tip of a chromosome.

Telophase : a stage of cell division when chromosomes relax and the nuclear membrane reforms.

Thymine : a pyrimidine base found in DNA but not in RNA.

Totipotent : describes a cell that can develop into any type f cell.

Uracil : a pyrimidine base found in RNA but not in DNA.

Zygote : a fertilized egg resulting from the fusion f a sperm and egg cell.

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