Sunday, 7 October 2012

Cramming for an exam on biotech

Although the lecturer said it'll be an exam with four essays, it can't hurt to clarify some of the key terms and themes concerning the basics of farm animal biotechnology. Ethical concerns and welfare issues are omitted - once I get started on that, there's no end to the rant.

Cloning: The practice of creating an animal from only one other animal of the same species. A cell sample, from skin or fur for example, is taken from the animal to be cloned. The nucleus is removed from one mature cell, and inserted into an egg cell, from which the nucleus has also been removed. The egg cell, now containing the genes of the animal to be cloned, is implanted on a female animal, which will eventually give birth to the cloned animal.

Genectic connection: For example, we might know that animals resistent to disease X have a mutation Y in their genome, while animals who suffer from X do not. Thus, even if it's not known which genes cause the resistance, the mutation Y can be used to  identify animals with X-resistance. Connections are deduced from the DNA of hundreds or preferably thousands of animals using statistical and genome analyzing tools.

Genetic marker: A piece of DNA, usually a microsatellite, which is connected to a specific trait. The marker can be either in a non-protein coding DNA or a part of the actual gene, in which case it is called the candidate gene. Markers are used to map genomes and to find genetic connections. Markers are not genes, and usually not active DNA at all. They can be thought of as genetic landmarks.

Marker assisted selection (MAS): The use of genetic markers linked to desired genes in breeding programmes. Animals can be selected to breeding based on traits which cannot be evaluated from the animal itself (like milk fat percentage from a bull) or while the animal is alive (such as pigs' carcass quality). When breeding choices are made from young animals and without genetic information, a male (like a popular dog) may pass on a serious disease to several offspring, before the male's sickness becomes known. MAS can be used to prevent this.

Microsatellite: A microsatellite is a short strand of DNA, which has a repetitive sequence of 2-4 bases, for example CACACACACACA. They are most often found in non-coding DNA. Microsatellites are found commonly on animal (including human) genome, and since they have a high polymorphism rate, they are often used in confirming descency and as genetic markers. Also known as STR or SSR for short tandem repeat or simple sequence repeat. Up to 30 % of a human genome consists of microsatellites, dinucleotine repeats being the most common.

Single-nucleotide polymorphism (SNP): SNP, pronounced snip, is a polymorphism of one nucleotide in DNA. A transition is when a purine is polymorphed to a purine or a pyriminide to a pyriminide (A to C, C to A, T to G, G to T). Transversion occurs when a purine is polymorphed to a pyriminide or vice versa. Both are explained clearly by Steven Carr.

Transgenesis: Inserting genes or other DNA material into a foreign cell. The original DNA can be taken from an animal of same or different species, and it may or may not be genetically modified. DNA can also be artificially created, and then inserted to the target cell. Transgenesis aims either at adding new properties, changing current properties or removing properties from the target.

Qualitative trait: A yes-or-no -trait, animal either has it or doesn't. Often an unwanted and monogenic trait, like a disease or bad meat quality. Whether a cow has horns or not is a qualitative, monogenic trait.

Quantitative trait: A trait, which is affected by several genes, possibly in several chromosomes. A polygenic trait, and often positive, such as milk yield in cows or large litter size in sows. A quantitative trait is described with a pluralistic variable like height, color, birth weight, milk yield or fat percentage. The color of a horse is defined by over 20 genes.

QTL/ETL: Quantitative trait locus / economic trait locus. Used to refer to a gene or a genetic marker related to a quantitative (polygenic) trait. Thus one gene solely responsible for a trait is not a QTL. QTLs for animals can be searched for example from

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