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Gene Expression
Level 2Biology
| Term | Definition |
|---|---|
| Allele | One of the alternative forms of a gene. |
| Amino acids | Any of a group of water-soluble organic compounds that possess both a carboxyl(-COOH) and an amine (-NH2) group attached to the same carbon atom. |
| Anticodon | A sequence of three nucleotides on a tRNA molecule that matches with a specific codon on a strand of mRNA during translation. |
| Centromere | The part of a chromosome that attaches to the spindle during cell division. |
| Chromatid | A threadlike strand formed from a chromosome during the stages of cell division. |
| Chromosome | A threadlike structure made of DNA and (in eukaryotes) associated histone proteins on which the genetic information of an individual is stored. |
| Cloning | artificial production of genetically identical individuals |
| Co-dominance | The condition that arises when both alleles in a heterozygous organism are dominant and fully expressed - eg. the human blood group AB. |
| Codon | A triplet of nucleotides within a molecule of messenger RNA that specifies a particular amino acid during the synthesis of proteins in a cell. |
| Diploid | Describing a cell or organism with twice the haploid number of chromosomes. |
| DNA | Deoxyribonucleic acid. The genetic material of most living organisms. It plays a central role in the determination of hereditary characteristics by controlling protein synthesis in cells. |
| Dominant allele | The allele that is expressed when two different alleles of a gene are present in the cells of an organism. It is denoted by a capital letter. |
| Double Helix | ladder-like molecule twisted into a helix |
| Eukaryotic cells | Cells that have a distinct nucleus where the cell’s genetic information is stored. |
| F1 generation | The first generation of offspring resulting from an arranged cross between selected parents in breeding experiments. |
| F2 generation | The second generation of offspring in breeding experiments, obtained by crosses between individuals of the F1 generation. |
| Fertilization | fusing of an egg and sperm |
| Gametes | A reproductive cell that fuses with another to form a zygote - eg. eggs (ova) and sperm (spermatozoa). |
| Gene | A section of DNA that codes for a particular protein and cannot be broken by recombination. |
| Genetic code | The genetic information in DNA which controls the manufacture of specific proteins by the cell. It takes the form of a series of triplets of bases in DNA. |
| Genome | All the genes contained in a single (haploid) set of chromosomes. |
| Genotype | The genetic composition of an organism, i.e. the combination of alleles it possesses. |
| Haploid | Describing a cell or organism with a single set of unpaired chromosomes. |
| Heterozygous | Describes an organism that has two different alleles controlling a particular feature. |
| Histone | Water-soluble proteins found in association with the DNA of eukaryotic chromosomes. They serve as a scaffold around which the DNA coils. |
| Homologous Chromosomes | Matching pairs of chromosomes, i.e. Chromosomes that have the same structural features. In diploid cells, one chromosome comes from the female parent, the other from the male parent. |
| Homozygous | Describes an organism that has two of the same alleles for a trait. |
| Incomplete dominance | The condition where neither allele controlling a characteristic is dominant and the resulting phenotype is partially influenced by both alleles. |
| Independent assortment | The separation of the alleles of one gene into gametes independently of the way in which the alleles of other genes have segregated. |
| Inheritance | The transfer of genetic traits from one generation to the next. |
| Lethal genes | A mutant form of a gene that eventually results in the death of an organism if expressed in the phenotype. Most of these genes are recessive, eg. Sickle-cell anaemia. |
| Meiosis | A type of cell division that gives rise to four gametes each with half the chromosome number of the parent cell. |
| Mitosis | A type of cell division that results in two daughter cells, each having a nucleus containing the same number and kind of chromosomes as the mother cell. |
| Monohybrid | The offspring of a cross between parents that differ in the alleles they possess for one particular gene, one parent having two dominant alleles, the other two recessives. |
| mRNA | RNA that carry’s the genetic code transcribed from DNA to the ribosomes. |
| Nucleotide | An organic compound consisting of a nitrogen-containing purine or pyrimidine base linked to a sugar and a phosphate group. |
| Phenotype | The observable characteristics of an organism. |
| Protein synthesis | The process by which living cells assemble amino acids into proteins based on the genetic information carried in the DNA of the chromosomes. |
| Purines | The chemical family to which the organic nitrogenous bases adenine and guanine belong. |
| Pyrimidines | The chemical family to which the organic nitrogenous bases uracil, thymine and cytosine belong. |
| Recessive allele | An allele whose effects are masked by those of a dominant allele. It is denoted by a lower case letter. |
| rRNA | A type of RNA that is present in the ribosomes. |
| DNA-Replication | ability of DNA molecules to make identical copies of themselves |
| Somatic cells | All cells in the body other than the reproductive cells. |
| Trait | feature whose appearance is determined by genes (inherited) |
| Transcription | The process in living cells in which the genetic information of DNA is transferred to a molecule of mRNA as the first step in protein synthesis. |
| Translation | The process in living cells in which a sequence of mRNA triplets (codons) is used to build a polypeptide chain during protein synthesis. |
| Triplet | A sequence of three nucleotides coding for a specific amino acid during protein synthesis. |