Biology - Dna

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trait.

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a particular characteristic or feature of an organism.

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gene.

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a unit of heredity that determines characteristics of an organism. at the molecular level, a gene is a

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genome.

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a whole set of genes in an organism.

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chromosome.

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the structure containing a single DNA molecule and associated proteins.
eukaryotes = in nucleus & visible during cell division.

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nucleosome.

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particle made of histone proteins around which DNA is coiled in a chromosome.

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locus.

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the position of a gene on a chromosome.

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ploidy.

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the number of sets of chromosomes in a cell.

HAploid = one set
DIploid = two sets

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replication.

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synthesis of DNA on a parent DNA molecule to produce two identical molecules.

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transcription.

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is the synthesis of a messenger RNA from a DNA template.

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RNA.

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a single stranded polynucleotide molecule containing the sugar ribose, phosphate and the bases. (adenine, guanine, cytosine and uracil)

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translation.

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the synthesis of a polypeptide chain from messenger RNA (mRNA).

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codon.

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the basic unit of the genetic code.

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gene regulation.

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involves processes that control gene expression, turning particular genes 'on' and 'off'.

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repressor.

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a molecule that stops transcription of a gene, by blocking RNA polymerase to the promoter region of the gene.

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restriction enzyme.

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a bacterial enzyme that recognises a short sequence of bases in a DNA molecule and cuts the DNA at this recognition site.

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gel electrophoresis.

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the migration and separation of DNA fragments along a gel, driven by a voltage drop.

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DNA profiling.

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the genetic make-up of an individual by cutting DNA into fragments using restriction enzymes and examining the banding pattern on an electrophoresis gel.

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probe.

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a purified fragment of single-stranded DNA that is labelled radioactively or with fluorescent dye. A probe hybridises with a complementary strand of DNA in a test sample, thus locating the particular segment.

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primer.

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a short piece of DNA synthesised to be complementary to a stretch of DNA. it hybridises to the larger stretch of DNA.

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DNA profile.

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is a unique banding pattern on a gel when an individual's DNA is cut with restriction enzymes.

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gene cloning.

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is the production of many identical copies of a gene.

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plasmids.

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small double-stranded DNA molecules that exist in bacteria independent of the bacterial chromosome.

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recombinant DNA.

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results from the insertion of a new piece of DNA into an organism's chromosome.

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interphase.

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the stage in the cell cycle during which various molecules are synthesised and DNA is replicated.

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mitosis.

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the stage in the EUKARYOTE cell cycle where chromosomes duplicate, sister chromatids separate and the nucleus of a cell divides. the genetic information in the two daughter nuclei is identical to that of the parent nucleus.

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cytokinesis.

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is the division of cytoplasm (cell division) following mitosis.

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meiosis.

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a reduction division. it involves one replication of DNA and two nuclear divisions that results in halving the number of chromosomes of a parent diploid nucleus to four haploid daughter nuclei (gametes).

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homologous chromosomes.

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a pair of similar chromosomes in a diploid organism; one chromosome is inherited from each parent.

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chromatid.

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is one of the two daughter strands of a replicated chromosome that are joined by a single centromere.

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mutation.

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a heritable change in genetic material.

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alleles.

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different forms of the same gene resulting from mutations.

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locus.

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a site on a chromosome where a particular gene is located.

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genotype.

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the particular combination of alleles present.

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phenotype.

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the character of observable trait of an organism.

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dominance/recessiveness.

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properties of a phenotype.

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dominant phenotype.

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one that is observed in the heterozygote and one homozygote.

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recessive phenotype.

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only observed in the homozygous condition.

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incomplete dominance.

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the phenotype is only partially expressed in the heterozygote. the phenotype of the heterozygote is different from either homozygote.

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co-dominant dominance.

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the phenotypes of both homozygotes are expressed equally in the heterozygote.

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monohybrid cross.

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a cross between two individuals involving a single genetic focus.

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pure-breeding strains.

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are homozygous at the locus of interest and produce genetically identical progeny.

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mendel's principle of segregation.

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states that individuals carry pairs of alleles of each gene which segregate into gametes during meiosis so that each gamete carries one allele into each gene.

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dihybrid cross.

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a cross between two individuals each involving two genetic loci.

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mendel's principle of independent assortment.

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states that the alleles of a gene controlling one trait assort independently of alleles of another gene controlling a different trait.

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testcross.

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involves crossing the F heterozygote with the parental strain showing the recessive phenotype.

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backcross.

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a cross between the F heterozygote and either one of the pure-breeding (homozygous) parental strains.

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linkage.

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the tendency for two or more genes located on the same chromosome to be inherited together.

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crossing over.

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the exchange of chromosomal material between members of a chromosomal pair during meiosis.

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chiasma.

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the point of crossing of strands of non-sister chromatids observed during the first division of meiosis.

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sex-linked inheritance.

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the inheritance pattern determined by genes located on the sex chromosomes.

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carrier.

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is an organism with an allele for a disease that is masked by a normal dominant phenotype. such an organism may not have the disease expressed, but might transmit the condition to its offspring where the disease might be expressed.

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pedigree analysis.

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the determination of the pattern of inheritance of a condition by reference to a family tree in which the presence or absence of the condition is recorded over generations.

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dominant phenotype.

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the observable characteristic that is evident in the heterozygote is referred to.

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discontinuous variation.

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occurs when the alternative phenotype are distinctively different from each other.