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Penetrance
| What it's not: |
A hypnotist’s mesmerizing gaze. The word was first used in the 19th century by Gilbert & Sullivan in their famous operetta about evil hypnotists called ‘The Pirates of Penetrance’ |
| What it is: |
This describes how often a trait is expressed for a particular genotype, regardless of the severity. Low penetrant diseases affect a small number of people with disease genotypes whereas almost all people are affected by highly penetrant diseases. Complete penetrance means that 100% of people with the disease mutation will have the associated phenotype. |
Phagocytosis
| What it's not: |
An excessive fear of the dangers of smoking cigarettes. |
| What it is: |
This term is literally 'cell eating'. Particles are engulfed by other cells and broken down by enzymes contained in specialized organelles (phagosomes). |
Phenotype
| What it's not: |
An ornate new font. |
| What it is: |
An organism’s traits that are expressed as it goes about its business. The phenotype is not a complete reflection of the genotype because some recessive alleles contained there are not expressed as traits in the organisms’ appearance or behavior. |
Plasticity Genes
| What it's not: |
Genes sometimes found in abundance in certain politicians. |
| What it is: |
Plasticity genes can adapt to the environment by regulatory bits that sense and directly respond to different environmental stimuli. For example, one gene could respond to the concentration of sugar in the blood. When blood sugar is high, the gene may be shut off and therefore do nothing. But when someone has very low sugar levels, the gene could turn on and help set up a hunger response. The term plasticity often comes up when discussing “nature vs. nurture” because one genotype can lead to different phenotypes in response to different environments. |
Polygenic
| What it's not: |
A term describing the genotypes of native inhabitants of certain islands in the South Pacific. |
| What it is: |
The term simply means ‘many genes’. Variation in some traits is due to the interaction of many genes, each with a small additive effect on the character in question. For example, it is currently believed that there are 3 genes involved in the determination of skin colour. |
Polymorphism
| What it's not: |
The act of constantly re-inventing oneself, like Madonna. |
| What it is: |
As the name suggests, this is ‘many forms’ of a DNA sequence or the presence of common variations of a DNA sequence. The difference between polymorphism and mutation is frequency – polymorphisms are more common, with the rarer allele present in at least 1% of the population. At one locus, if two alleles are 98% and 2%, you have a polymorphism. But if the rarer allele is only present in only 0.2% of the population, it is a mutation.
It is often quoted that your DNA and mine are 99.9% the same. But it’s the 0.1% that makes us different from each other, sometimes spectacularly so. Oftentimes, that difference can be in just one letter (base) in one’s DNA, an A where your friend has a G, for example. This tiny difference is called a Single Nucleotide Polymorphism. SNPs (‘snips’ to the initiated) are a significant focus of current genomics research. |
Preimplantation Genetic Diagnosis (PGD)
| What it's not: |
A new treatment for male patterned baldness. |
| What it is: |
PGD is a new technology that allows embryos to be tested for a genetic
condition before transferring embryos to the mother’s uterus. PGD is an
option for couples who are at risk of passing on a genetic condition.
Using IVF technology, some of the mother’s eggs are removed and
fertilized with sperm in the lab. Once the embryo has grown to the 6-8
cell stage, one cell is removed and genetic testing is done. Only those
embryos that are not affected with the genetic condition tested are
implanted in the mother’s uterus. |
Prevalence
| What it's not: |
A fancy French window covering. Ooh la la. |
| What it is: |
Prevalence describes the total number of existing cases of a condition in a population at a specific point in time. For example, the World Health Organization estimates that over 177 million people have diabetes. |
Primer
| What it's not: |
A teacher of kindergarten, or grades one, two, or three. |
| What it is: |
A primer is a short nucleic acid chain that serves as a starting point
for DNA replication. To replicate DNA, it is first unwound into single
strands but the enzyme that makes the new strand (DNA polymerase)
doesn’t put down complementary nucleotides anywhere, it needs a
starting point for replication = the primer. The DNA polymerase can
only elongate a nucleotide chain; it can’t synthesize a new DNA strand
from scratch. Primers are short stretches of DNA that are complementary
to the template strand. In other words, if you want to copy
“CATCATCATCAT”, a 3 nucleotide primer would be “GTA”. In most natural
DNA replication, the primer for DNA synthesis is a short strand of RNA
that is later replaced by DNA. The requirement of primers for DNA
replication has become an advantage in the lab for molecular biology
techniques such as sequencing and PCR because the primer identifies the
start point for the amplification. |
Promoter
| What it's not: |
The people who give you free samples advertising their company at festivals. You can never get enough free magnets or pens! |
| What it is: |
The promoter is a region of the gene located at the beginning (5’ end). It contains sequences important in starting transcription. There are similarities in sequence for promoters of different genes. Mutations in the promoter region may cause incorrect expression of the gene and can lead to disease. |
Protein
| What it's not: |
The positive attitude of someone who likes helping adolescents. |
| What it is: |
Proteins are made up of various combinations of amino acids. They support living organisms’ shape & structure in tendon, ligament and claw; carry messages within cells & between them; and as enzymes, they regulate the chemical processes that sustain our and other organisms’ lives. |
Protein Synthesis
| What it's not: |
A high school teachers’ conference. |
| What it is: |
in the The complex process of building proteins from the amino acid sequences represented by codonsgenes in DNA. In a nutshell (actually in a cell), the process is as follows.
In the cell’s nucleus, the DNA strand unwinds at various points along its length. Molecules of mRNA make copies of specific genes, take them out of the nucleus & into the cytoplasm, specifically to the ‘assembly area’ called a ribosome. Once there, the ribosome ‘reads’ along the mRNA, each triplet of bases along its length representing an amino acid. Molecules of transfer RNA (tRNA) bring the corresponding amino acid to the correct place in the protein under construction. When it reaches a codon representing ‘stop’, the ribosome disengages from the mRNA string. The amino acid chain being complete, the now decoded chain breaks free, folds up into its characteristic shape and goes about its life-sustaining business as a protein. If you’re really interested in as complete a description of protein synthesis as any layperson would ever want, see Steven Rose. The Chemistry of Life. (Toronto: Penguin Books of Canada Ltd., 1999), Pages 210-250. |
Proteomics
| What it's not: |
The Proteomes’ philosophy of life (similar to Epicureanism). |
| What it is: |
The
science that studies the expressed protein component of the genome.
Initially aimed at cataloguing the proteins present in a cell under
various conditions, proteomics has joined up with genomics to try to
understand how the expression of the genome enables all the complex
functions of the cell to work. |
Punnet Square
| What it's not: |
The newest craze in square dancing. Yee Haw. |
| What it is: |
A Punnet Square is a diagram that illustrates all the possible genotype combinations from a mating. One parent’s genotype is writeen on the top row and the genotype of the other parent is written along the left side. In the table below, both the parents have the genotype Dd. From this table we can say that ¼ of the offspring will have the genotype DD, ¼ will have the genotype dd, and ½ off the offspring will be heterozygous Dd.
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