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P

P1-derived artificial chromosome (PAC)
One type of vector used to clone DNA fragments (100- to 300-kb insert size; average, 150 kb) in Escherichia coli cells. Based on bacteriophage (a virus) P1 genome.
See also: cloning vector

Patent
In genetics, conferring the right or title to genes, gene variations, or identifiable portions of sequenced genetic material to an individual or organization.
See also: gene

Pedigree
A family tree diagram that shows how a particular genetic trait or disease has been inherited.
See also: inherit

Penetrance
The probability of a gene or genetic trait being expressed. "Complete" penetrance means the gene or genes for a trait are expressed in all the population who have the genes. "Incomplete" penetrance means the genetic trait is expressed in only part of the population. The percent penetrance also may change with the age range of the population.

Peptide
Two or more amino acids joined by a bond called a "peptide bond."
See also: polypeptide

Phage
A virus for which the natural host is a bacterial cell.

Pharmacogenomics
The study of the interaction of an individual's genetic makeup and response to a drug.

Phenocopy
A trait not caused by inheritance of a gene but appears to be identical to a genetic trait.

Phenotype
The physical characteristics of an organism or the presence of a disease that may or may not be genetic.
See also: genotype

Physical map
A map of the locations of identifiable landmarks on DNA (e.g., restriction-enzyme cutting sites, genes), regardless of inheritance. Distance is measured in base pairs. For the human genome, the lowest-resolution physical map is the banding patterns on the 24 different chromosomes; the highest-resolution map is the complete nucleotide sequence of the chromosomes.

Plasmid
Autonomously replicating extra-chromosomal circular DNA molecules, distinct from the normal bacterial genome and nonessential for cell survival under nonselective conditions. Some plasmids are capable of integrating into the host genome. A number of artificially constructed plasmids are used as cloning vectors.

Pleiotropy
One gene that causes many different physical traits such as multiple disease symptoms.

Pluripotency
The potential of a cell to develop into more than one type of mature cell, depending on environment.

Polygenic disorder
Genetic disorder resulting from the combined action of alleles of more than one gene (e.g., heart disease, diabetes, and some cancers). Although such disorders are inherited, they depend on the simultaneous presence of several alleles; thus the hereditary patterns usually are more complex than those of single-gene disorders.
See also: single-gene disorder

Polymerase chain reaction (PCR)
A method for amplifying a DNA base sequence using a heat-stable polymerase and two 20-base primers, one complementary to the (+) strand at one end of the sequence to be amplified and one complementary to the (-) strand at the other end. Because the newly synthesized DNA strands can subsequently serve as additional templates for the same primer sequences, successive rounds of primer annealing, strand elongation, and dissociation produce rapid and highly specific amplification of the desired sequence. PCR also can be used to detect the existence of the defined sequence in a DNA sample.

Polymerase, DNA or RNA
Enzyme that catalyzes the synthesis of nucleic acids on preexisting nucleic acid templates, assembling RNA from ribonucleotides or DNA from deoxyribonucleotides.

Polymorphism
Difference in DNA sequence among individuals that may underlie differences in health. Genetic variations occurring in more than 1% of a population would be considered useful polymorphisms for genetic linkage analysis.
See also: mutation

Polypeptide
A protein or part of a protein made of a chain of amino acids joined by a peptide bond.

Population genetics
The study of variation in genes among a group of individuals.

Positional cloning
A technique used to identify genes, usually those that are associated with diseases, based on their location on a chromosome.

Premature chromosome condensation (PCC)
A method of studying chromosomes in the interphase stage of the cell cycle.

Primer
Short preexisting polynucleotide chain to which new deoxyribonucleotides can be added by DNA polymerase.

Privacy
In genetics, the right of people to restrict access to their genetic information.

Probe
Single-stranded DNA or RNA molecules of specific base sequence, labeled either radioactively or immunologically, that are used to detect the complementary base sequence by hybridization.

Prokaryote
Cell or organism lacking a membrane-bound, structurally discrete nucleus and other subcellular compartments. Bacteria are examples of prokaryotes.
See also: chromosome, eukaryote

Promoter
A DNA site to which RNA polymerase will bind and initiate transcription.

Pronucleus
The nucleus of a sperm or egg prior to fertilization.
See also: nucleus, transgenic

Protein
A large molecule composed of one or more chains of amino acids in a specific order; the order is determined by the base sequence of nucleotides in the gene that codes for the protein. Proteins are required for the structure, function, and regulation of the body's cells, tissues, and organs; and each protein has unique functions. Examples are hormones, enzymes, and antibodies.

Proteome
Proteins expressed by a cell or organ at a particular time and under specific conditions.

Proteomics
The study of the full set of proteins encoded by a genome.

Pseudogene
A sequence of DNA similar to a gene but nonfunctional; probably the remnant of a once-functional gene that accumulated mutations.

Purine
A nitrogen-containing, double-ring, basic compound that occurs in nucleic acids. The purines in DNA and RNA are adenine and guanine.
See also: base pair

Pyrimidine
A nitrogen-containing, single-ring, basic compound that occurs in nucleic acids. The pyrimidines in DNA are cytosine and thymine; in RNA, cytosine and uracil.
See also: base pair


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