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Semidominant
| What it's not: |
A personality trait of a person in a passive-aggressive, co-dependent relationship |
| What it is: |
Semidominance is when a heterozygote (Aa genotype) has a phenotype that is half-way (intermediate) to what is seen with both homozygotes (AA or aa). Both alleles of the gene interact with each other and are partly expressed in the heterozygote. For example, if you cross a red carnation with a white carnation you get pink carnations. Both the red ‘A’ allele and the white ‘a’ allele are being partially expressed in the phenotype. |
Sequencing
| What it's not: |
The act of sewing sparkly decorations on dresses. |
| What it is: |
Sequencing refers to the reading of the residues within a molecular chain of building blocks. In other words, it is determining the order of nucleotides in a DNA or RNA chain or the amino acids within a polypeptide. On our site, we often talk about DNA sequencing– the reading of genetic information. By learning the complete human DNA sequence, scientists hope to gain new insights into biology, learn to diagnose and predict disease better, and develop new technologies. |
Sex-linked
| What it's not: |
What people sometimes feel toward one another. |
| What it is: |
The tendency of certain characteristics to appear in one sex. Red-green colour blindness, for example, is a man-thing, as is hemophilia. Even though these conditions caused by recessive traits are found almost exclusively in human males, they are fundamentally determined by X chromosome genes. The reason that males show the disease is that they have only one X chromosome. It seems backwards because women have two X chromosomes so they should have more X diseases. BUT, women have two alleles of each gene so if one allele is mutated to be nonfunctional, the other allele can compensate. If a man’s one allele is mutated, there is nothing to cover it so he has that particular disease. In the case of the X-linked dystrophin gene, a severe mutation that can’t make any dystrophin protein: men have Duchenne muscular dystrophy and women are OK. They’re probably not professional athletes but they’re OK for normal muscles, because women have 50% of dystrophin and that is enough for functioning normally. |
SNP (single nucleotide polymorphism)
| What it's not: |
Salt n’ Pepper
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| What it is: |
A single nucleotide polymorphism is a variation in a single base (A, T, C or G) within a sequence of DNA. For any single base variation to be called a SNP it must be found in more than 1% of the population. So far more than 6 million SNPs have been discovered in the human genome. SNPs do not generally cause disease directly but some SNPs may affect an individual’s susceptibility to disease or the response to the drugs and treatments.
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Soft Marker
| What it's not: |
A special erasable marker that can be used to write on all types of surfaces.
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| What it is: |
An ultrasound ‘soft marker’ is a variation of normal fetal anatomy. An ultrasound marker is NOT an abnormality. Soft markers are seen in healthy, normal pregnancies but when a soft marker is seen, it increases the risk that there is a chromosome problem in the baby. For example, extra fluid behind a baby’s neck (called ‘nuchal translucency’) is a marker. This extra fluid can be seen in healthy, unaffected babies but it is seen more often in babies with a chromosome problem, such as Down syndrome.
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Somatic Cell Nuclear Transfer
| What it's not: |
What happened at Chernobyl. |
| What it is: |
This method requires 2 donors: a nucleus and an egg. The ‘clonee’ donates its nucleus – which of course includes its DNA – and the nucleus is put into a nucleus-free egg. Once this happens, the egg is tricked into believing it is a fertilized zygote. Remember, the nucleus of an egg only has half the amount of DNA as a regular cell and normally adding sperm gives it the necessary complement. By adding a nucleus with a full amount of DNA, however, no fertilization is required. The egg is needed to provide nutrients to the developing embryo. But cloning isn’t easy – the cloned nucleus has to be stripped of all its previous instructions so that it has the potential to become anything, not just the same kind of cell it was taken from. One way to do this is to starve the cell of required nutrients. After the nucleus is put into the donor egg, an electric charge is applied to fuse the cell and nucleus together. If all goes well, the cell will divide & differentiate, eventually producing an embryo that will develop into a copy (clone) of the organism that donated the nucleus.
Although cloned animals are in the news these days, cloning is far from being an ‘everyday scientific activity’. It is still technically demanding and relatively inefficient. To create the famous cloned sheep, Dolly, 277 nuclei were transferred to eggs, which resulted in only 29 embryos. And only Dolly survived the entire process of development. In August 2005, an Afghan hound was cloned with the somatic cell nuclear transfer method, but he was the only one of 1095 embryos implanted in 123 dogs to survive to be a healthy puppy. |
Somatic Cells
| What it's not: |
Where characters in Aldous Huxley’s Brave New World took their drugs. |
| What it is: |
The cells that form the body only. Mutations in these cells are not passed on to the next generation. Therefore, applying gene therapy to fix a mutation in your somatic cells would only affect you. For example, gene therapy to replace a missing gene in white blood cells will treat SCID, but will not permanently change future generations’ DNA. Because of this, alterations to somatic cell DNA can be seen as safer because the change is limited to one individual. |
Spina Bifida
| What it's not: |
Bif Naked's back-up singer
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| What it is: |
Spina bifida is a condition where the bones of the spine (vertebrae) do not close properly around the spinal cord. The gap in the spinal bones means that part of the spinal cord is exposed and nerve damage occurs. How much nerve damage occurs depends on the size and location of the vertebrae gap. Spina bifida can occur alone or as part of a syndrome with other multiple birth defects. The exact cause of spina bifida is unknown however it is thought that both environmental factors and genetic factors play a role (multifactorial inheritance). |
Sporadic
| What it's not: |
The newest dance move to hit the clubs.
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| What it is: |
Sporadic is when something happens by chance or at random, for unknown reasons. For example, if one person in a family had a genetic condition that was not found in any other family members, they may be referred to as having a sporadic case of that condition.
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Stem Cell
| What it's not: |
What you cut when arranging flowers. |
| What it is: |
The unspecialized cells that all the cells in our bodies descend from. A fertilized egg is called a totipotent stem cell because it can differentiate into an entire organism. So-called pluripotent and multipotent stem cells are a little more limited in creative capacity. The former, found in embryos in the very early stages of development, can become any kind of cell (but they can’t make an entire organism). The latter (multipotent stem cells) can develop into a limited set of cell types. Even though these kinds of stem cells are found in adult organs, their numbers are very small. Since stem cells can divide indefinitely under the right conditions, their importance to research in replacing damaged cells in the body is extremely significant. Ethical questions concerning the harvesting of embryonic stem cells from aborted fetuses are also extremely significant. |
Sticky End
| What it's not: |
The end you never take when offered anything. |
| What it is: |
When DNA is cut with enzymes, the cut can be clean (blunt) or angled (sticky) and it depends on the restriction enzyme site. The enzyme EcoRI has the following recognition site indicated by ↑ or ↓:
Original Sequence cut
G↓A A T T C
C T T A A↑G
leads to
Fragment 1
G
CTTAA
Fragment 2
AATTC
........G
These overhangs (the base letters in the two fragments above) are the sticky ends. DNA strands with complementary sticky ends can stick together to form recombinant DNA strands. |
Spina Bifida |
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