Glossary
Genetics glossary
914 definitions · page 16 of 16.
- plasmid
- Autonomously replicating extrachromosomal DNA molecule. An autonomous self-replicating genetic particle usually of circular double-stranded DNA.
- plastid
- A chloroplast prior to the development of chlorophyll.
- plate
- (1) A flat dish used to culture microbes. (2) To spread cells over the surface of solid medium in a plate.
- pleiotropic mutation
- A mutation that has effects on several different characters.
- pleiotropy
- The phenomenon whereby a single mutation affects several apparently unrelated aspects of the phenotype.
- point mutation
- A mutation that can be mapped to one specific site within a locus. A small mutation that consists of the replacement (transition or transversion); addition; or deletion (frameshift) of one or a few bases.
- Poisson distribution
- A mathematical expression giving the probability of observing various numbers of a particular event in a sample when the mean probability of that event on any one trial is very small.
- poky mutation
- A mutation of Neurospora that produces a petite-like phenotype.
- polycistronic mRNA
- An mRNA that codes for more than one protein.
- polytene chromosome
- A giant chromosome produced by an endomitotic process in which, following synapsis of the two homologues, multiple rounds of replication produce chromatids that remain synapsed together in a haploid number of chromosomes. Large chromosome consisting of many…
- position effect
- Used to describe a situation in which the phenotype expressed by a gene is altered by changes in the position of the gene within the genome. For instance genes translocated to regions of heterochromatin are often not expressed.
- Pribnow box
- Relatively invariant sequence of six nucleotides (concensus TATAAT) in prokaryotic promoters centred at the position minus 10 (10 base pairs upstream from the transcription start site).
- pyrimidine
- Nitrogenous bases of which thymine is found in DNA; uridine in RNA; and cytosine in both.
- quantitative inheritance
- The mechanism of genetic control of traits showing continuous variation.