A patent is a government granted monopoly on an invention
A patent is a government-granted monopoly on an invention to an inventor or their assignee for a limited period of time in exchange for a public disclosure of an invention. The term “limited period of time" mean the maximum period during which patent can be maintained into force. It is usually expressed in number of years (typically up to twenty years) either starting from the filing date of the patent application or from the date of grant of the patent. As long as the patent is valid the owner has to pay a yearly fee in order to keep the patent in force. Otherwise the patent will be lapsed before its term. [1; 2]
Patents are exclusively national affairs, so patent that was issued in one country cannot provide protection of the invention in the any other countries in the world. However some countries have concluded treaties under which patents can be granted, and these patents automatically become valid in all treaty members.
Description of main Patent Types:
International applications (or PCT applications) are the patent application that filed under the Patent Cooperation Treaty (PCT).
The two things should be notes about international applications. First of all, these applications do not give any international protection to the applicant. The applicant is free to claim whatever he wants, so it can easily happen that applicant claims something that is useless, long known or totally trivial. Second, WIPO do not get any responsibility for the issuing patents in the any of the PCT countries. It is just aloud to file one application centrally and to get one literature search done, before going to the various national patent offices for examination. After the publication and the search, the application and the results of the search are sent to all the national patent offices indicated on the front page of the publication. The applicant then has to enter national phase (foreign filings) of the countries of his choice within the time limits to do so and defend his claims to get a patent in those national offices. Indeed PCT applications unlike most patent applications can never result in a patent.
However PCT applications provide several benefits to applicants:
It allows the applicant to delay the expenses of filing applications around the world.
Applicant can do some voluntary amendments to the claims as a result of the literature search before his application will be published like PCT application and sent to the national patent authorities around the world.
It allows the applicant to get opportunities for international examination, which will give an early indication of patentability in PCT countries.
By filing a PCT application, the applicant can postpone for 30 months (rather than 12 months under the Paris Convention) the decision on patenting His/her invention in the others PTC countries. It allows the inventor more time to assess the commercial viability of his/her invention.
And many inventors all over the world try to get this type of application at the beginning.
European patents and applications:
The term European patent is used to refer to patents granted under the European Patent Convention (EPC).
Two ways can be appropriate for getting European patent. First of all, Inventor can file patent application directly with the country or countries in EU in which patents are desired. And second, inventor can do single filing of a patent application with the European Patent Office (EPO). European Patent Office is the official organization which actual legislative power proceeds from EPC. The EPO is not a body of the European Union and patent granted by the EPO does not lead to a single European Union-wide patent. However the European Patent Office offers a way to file a single patent application which can lead to patent coverage in all the European countries that belong to the EPC. A European patent gives the same rights as national patents in the EPC countries chosen by the applicant. In fact European patent get a legislation power thro independent national patents in the EPC countries of choice. Once granted, a European patent can only be annulled by separate proceedings in each country. However, during the first nine months after the grant of the patent, anyone can start an opposition procedure at the EPO to annul the patent in all these countries at once.
Usually if it is only desired to get patent coverage in one or two countries of Europe, it may be cheaper to file directly with the patent offices in those countries. On the other hand, if the number of countries of Europe in which patent protection is desired is much greater than just one or two countries, then it would be economical to file directly with the European Patent Office.
US patents and applications:
US patents and applications can be defined as a patents and applications granted under the United States patent law. The provisions of the law are laid out in Title 35 of the United States Code (U.S.C.) and give authority for the United States Patent and Trademark Office (USPTO).
The present situation is that the patents are territorial in nature, by this mean that in each country patents granted under the own country’s national laws. However there is a trend towards global harmonization of patent laws and granting procedures.
A key international documents relating to the patent law harmonization are the Paris Convention for the Protection of Industrial Property and the Agreement on Trade Related Aspects of Intellectual Property Rights (TRIPS)
The Paris Convention for the Protection of Industrial Property, signed in Paris, France, on March 20, 1883, was one of the first intellectual property treaties. As a result of this treaty, intellectual property, including patents, of any contracting state are accessible to the nationals of other states party to the Convention. Paris Convention for the Protection of Industrial Property sets out a range of basic rules relating to patents, the principles of the convention are incorporated into all notable current patent systems.
The Agreement on Trade Related Aspects of Intellectual Property Rights (TRIPS) is an international agreement administered by the World Trade Organization (WTO). It was negotiated at the end of the Uruguay Round of the General Agreement on Tariffs and Trade (GATT) in 1994. The TRIPs Agreement has been largely successful in providing a forum for nations to agree on an aligned set of patent laws. Conformity with the TRIPs agreement is a requirement of admission to the WTO and so compliance is seen by many nations as important.
There main international treaty in the area of harmonization of a patent granting procedures are the European Patent Convention (EPC) (administered by the European Patent Organisation (EPO)), and the Patent Cooperation Treaty (PCT) (administered by World Intellectual Property Office (WIPO)), that centralize some portion of the filing and examination procedure.
European patent law
European patent law covers a wide range of legislations including national patent laws, the Strasbourg Convention of 1963, the European Patent Convention of 1973, and a number of European Union directives and regulations.
European patent law is also shaped by international agreements such as the World Trade Organization's Agreement on Trade-Related Aspects of Intellectual Property Rights (TRIPs Agreement), Paris Convention for the Protection of Industrial Property, Patent Cooperation Treaty (PCT) and the Patent Law Treaty (PLT).
The Patent Law Treaty (PLT) is a patent law multilateral treaty concluded on 1 June 2000 in Geneva, Switzerland, by 53 States and the European Patent Organisation. Its aim is to harmonize formal procedures such as the requirements to obtain a filing date for a patent application, the form and content of a patent application, and representation.
United States patent law
The provisions of the law are laid out in Title 35 of the United States Code (U.S.C.) and give authority for the United States Patent and Trademark Office.
United States is a part of World Trade Organization's Agreement on Trade-Related Aspects of Intellectual Property Rights (TRIPs Agreement), Patent Cooperation Treaty (PCT) and Paris Convention for the Protection of Industrial Property.
Differences between US and European patents 
While quite a few aspects of patent law have been harmonized internationally, there still are many important differences between the two systems. The main differences between US and European patents are listed below.
First to file versus first to invent
First to file and first to invent are legal concepts that clarified definition of priority right to the grant of a patent for an invention. The first to file system is the prevalent system in the majority of countries, virtual all European Countries use this system of priority. Nevertheless United States define priority using rather different first to invent system.
First to file is a system in which the first person to file a patent application will be awarded a patent (assuming the invention is patentable, of course), regardless of the date of actual invention. Even if the second person did in fact come up with the invention first, the only thing that counts is the filing date.
In the First to invent system, a slightly different concept of priority is used. In case of two applications for the same invention (a so-called interference), a determination of priority is made base on information about date when invention was actually invented. This usually involves examining laboratory logbooks, establishing dates for prototypes, and so on. If the person who filed later is found to have invented earlier, he may be awarded the patent.
Grace period is a period of time within which inventor is allowed to file an application for patent even after it became publicly available ("Publicly available" includes selling the invention, giving a lecture about it, showing it to an investor without a non-disclosure agreement (NDA), publishing it in a magazine, and so on.). The USA has a one-year grace period (35 US Code section 102). However, this only applies for the USA. In Europe if the invention has become publicly available in any way before the patent application was filed, the application will be rejected (Article 54 EPC). It does not make a difference whether the person making it publicly available is the inventor, one of the inventors, or an independent third party.
Best mode requirement
The best mode requirement is essential for the US patent law and generally not found in other national patent jurisdictions. According to this requirement, the inventor must include the best way to practice the invention in the patent application (35 US Code section 112). Hence the inventor cannot get a patent and still keep some essential or advantageous aspect a secret.
In contrast, European patent law has no such requirement. At least one way of practicing the invention must be included in the application (Article 83 EPC), but there is nothing that states this way must be the best way, or even a good way.
Publication of patent applications
Both in the Europe and US patent applications are published 18 months after their filing date, unless they have been withdrawn. Publication of a patent application is not an indication of the patentability of the invention in any way; it only means that the application is 18 months old. It should be noted that in US patent application can be submitted to the patent authority with a non-publication request, stating that the application is US only. Europe has not such non-publication request practice.
While US patent and US patent application have different systems of numeration, determinative header and independent databases, the EPO application and a granted patent have no such features which allowed to simply distinguishing them. Whatever it is EPO application or granted patent can be figured out in two ways. First, the number in the top-right corner (kind code) has an "A" when the publication is an application and a "B" when it is a patent. Second, granted European patents do not have an abstract on the front cover.
Rights conferred by a granted patent
A US patent is a property right which is enforceable in the whole territory of the USA. It allows the patent holder to prevent anyone from making, using or selling in the USA the patented invention. This is because the US patent law (35 US Code) is a federal statute.
In contrast, the European Patent Convention is a treaty signed by twenty-seven European countries. A granted European patent under the EPC confers to its owner the same right as a national patent in those EPC countries he elected in the application. So, essentially, a European patent changes into a "bundle" of national patents.
Opposition after grant
Within nine months after the grant of a European patent, anyone can file an opposition with the EPO, stating why this patent should not have been granted (of course with arguments and evidence). The patent holder and the opponent can then debate with each other. Finally, the EPO will take a decision based on facts and arguments presented by both sides.
While the USA has a reexamination procedure, it does not work the same as an opposition. In a reexamination, anyone can present reasons and evidence to the USPTO to challenge the validity of a granted patent. However, it is then the patent holder who engages in a discussion with the USPTO examiner to establish the validity of the reasons. The challenger is not a part of these proceedings.
The two most important requirements in European patent law are that, to be patentable, an invention must be novel and involve an inventive step (Article 52 EPC). An inventive step is defined by EPO like step which contain solution of a technical problem in a non-obvious way. This is comparable to the US requirement that the invention must be novel and must not be obvious (35 US Code sections 102 and 103). In fact, the Patent Cooperation Treaty, which streamlines the filing process in its member country, also requires that an invention be novel and involve an inventive step, but states that being non-obvious is sufficient to involve an inventive step.
European patents and applications typically ("wherever appropriate") contain so-called two-part claims (since this is required by Rule 29 of the European Patent Convention). First part of this claim (independent claim) lists some features “those technical features which are necessary for the definition of the claimed subject-matter but which, in combination, are part of the prior art", and the second part of this claim (dependent claim) contains one or more further features which are typically linked with the first parte by phrases such as "with an improvement of", "characterized in that" or "with an improvement comprising" and so on. Those latter features are what constitutes the invention (and so are often called the characterizing features).
In contrast, US patents and patent applications will almost always have one-part claims. However it is possible to get two-part claim in the US, this type of claims (also called "Jepson claims") are judged using very strict (compare to Europe) rule: anything before the characterizing portion is regarded to be prior art by definition. If any of the novel features will be putted by accident in the precharacterizing part, it's regarded as prior art and may damage the patentability. This makes US patent practictioners wary of using this construct. By comparison in Europe this accident will not affect the patentability directly and inventor will be simply asked to move that feature to the characterizing portion.
Determining the scope of a patent 
The scope of a patent is defined by the claims. The claims (typically found at the end of a patent document) provide a definition of what the patent exactly protects, this include all the essential elements of the invention. Terms used in a claim may be defined by the whole document, but ultimately only what is described in the claims is protected. Claims used to define the validity of a patent (by comparing them against the prior art. If the claims contain one feature that is not mentioned in the prior art, the invention is new. If the one new feature is not obvious, then the claim is patentable) and to make a decision about infringement of exclusive rights which is gave thro the patent protection. To infringe the patent, each and every element of a claim must be present in the infringing product. If even a single element is missing, the product does not infringe. It doesn't matter if the patent document says that that single element is optional: if it is in the claim, it is required.
Although the literal wording of the claims is the most important, there are still ways to extend the scope of a patent beyond this literal wording. Some of the main extending methods are described below.
Infringement through equivalence (doctrine of equivalents)
The doctrine of equivalents is a legal rule in most of the world's patent systems that allows a court to make a decision about patent infringement even though the infringing device or process does not fall within the literal scope of a patent claim, but nevertheless is equivalent to the claimed invention. When and how something is an equivalent of a term in a patent claim is a matter of national patent law. The scope of equivalence varies from country to country, and even within one country it can vary with time. However some attempts have been made to harmonize the doctrine of equivalents.
For instance, Article 21(2) of 1991 WIPO's "Basic Proposal" for a Treaty Supplementing the Paris Convention states:
"(a) (...) a claim shall be considered to cover not only all the elements as expressed in the claim but also equivalents.
(b) An element ("the equivalent element") shall generally be considered as being equivalent to an element as expressed in a claim if, at the time of any alleged infringement, either of the following conditions is fulfilled in regard to the invention as claimed:
(i) the equivalent element performs substantially the same function in substantially the same way and produces substantially the same result as the element as expressed in the claim, or
(ii) it is obvious to a person skilled in the art that the same result as that achieved by means of the element as expressed in the claim can be achieved by means of the equivalent element."
The doctrine of equivalence is also influenced by the state of the art: something that is already known cannot infringe on a patent through the doctrine of equivalence.
Broad terms and Redefining terms to increase the scope
Arbitrary defining of terms in patents is usually permissible, and can significantly broader the scope of a patent. However, the use of broad terms also has its limitations; a court could rule that the scope of the claim is too broad. This is why many patents contain lists of possible alternative ways to do the same thing. Another issue is what is known in the state of the art: something that is already known cannot be a subject of a patent, in this situation inventor have to narrow down claims’ definitions.
Dependent claims as fallback positions
Typically patent include more than one claim. Some of these claims refer back to other claims. They are called "dependent" claims, since part of the definition they provide depends on those other claims. Dependent claims often cover advantageous ways to realize the invention. They can be used as fallback positions in case the independent claim is rejected or annulled by a court.
Patenting of Genetic Inventions
The biotechnological inventions in the patent system are similar to chemical inventions. These include inventions, which are biological, microbiological, genetic engineering, medical, and agriculture. The US Courts and EPO have granted patents to genetic inventions, however, the issue of patentability of genes and gene sequences is yet not settled. In the case of discussion genetic inventions patentability main consideration should be given to the Conditions of patentability, which is listed below.
Conditions of patentability
Substantive conditions of patentability:
Gateway requirement (Is it patentable subject mater?)
Non-Obviousness (in United States patent law); Inventive step (Is it invention or discovery?) (in European patent law).
Usefulness (in United States patent law); Susceptibility of industrial application (in European patent law).
Additional requirements (ethic, public order and morality)
Formal conditions of patentability:
Sufficiency of disclosure.
Unity of invention.
Best mode requirement.
Some of these conditions, like Novelty, Sufficiency of disclosure and Best mode requirement, are obvious, because they will be used in the same way for the genetic inventions like for any other kind of inventions. And some of these conditions, like Non-Obviousness/ Inventive step, Usefulness/ Susceptibility of industrial application and Utility of invention (which is in fact the part of two previous requirements), are very tricky implemented to the genetic inventions and will be discussed further down.
Additional requirements (ethic, public order and morality) lying below the scope of this overview and will not be examine below.
In principle all genetic inventions are fall into category of biotechnological inventions.
Article 27(1) of the TRIPS Agreement  clearly states that patents should be granted for inventions in any field of technology without discrimination, subject to certain clauses:
“…patents shall be available for any inventions, whether products or processes, in all fields of technology, provided that they are new, involve an inventive step and are capable of industrial application."
This implies that biotechnological inventions are patentable subject matter. Hence all genetic inventions are patentable subject matter.
Non-Obviousness (in United States patent law); Inventive step (in European patent law).
This criterion is a center of a “patenting of life" debate. The US Courts and EPO have granted patents to genetic inventions; however, the issue of patentability of genes and gene sequences is yet not settled. A number of arguments are advanced against the patentability of genes, which are given below:
Genes are naturally occurring
Genes are basically discoveries, i.e. the invention claimed is actually a disclosure of something already in existence.
The process involves gene isolation and cloning, which are well known processes
In the EPC Countries the issue can be clarified using Guidelines for Examination in the EPO, C:IV 2.3.1 (Discoveries)  which states that:
“To find a previously unrecognised substance occurring in nature is also mere discovery and therefore un-patentable. However, if a substance found in nature can be shown to produce a technical effect it may be patentable. An example of such a case is that of a substance occurring in nature which is found to have an antibiotic effect. In addition, if a microorganism is discovered to exist in nature and to produce an antibiotic, the microorganism itself may also be patentable as one aspect of the invention. Similarly, a gene which is discovered to exist in nature may be patentable if a technical effect is revealed, e.g. its use in making a certain polypeptide or in gene therapy".
This guide lines based on further, Rule 27 of the European Patent Convention (EPC) (Patentable biotechnological inventions) :
“Patentable biotechnological inventions shall also be patentable if they concern: (a) biological material which is isolated from its natural environment or produced by means of a technical process even if it previously occurred in nature…"
Also some main information about patentability of genetic invention in Europe lades out in the Biotechnology Directive (98/44/EC).
Directive 98/44/EC of the European Parliament and of the Council of 6 July 1998 on the legal protection of biotechnological inventions is a European Union directive in the field of patent law, made under the internal market provisions of the Treaty of Rome. It was intended to harmonize the laws of Member States regarding the patentability of biotechnological inventions, including plant varieties (as legally defined) and human genes.
Article 5 of the Biotechnology Directive (98/44/EC)  states:
“1. The human body, at the various stages of its formation and development, and the simple discovery of one of its elements, including the sequence or partial sequence of a gene, cannot constitute patentable inventions.
2. An element isolated from the human body or otherwise produced by means of a technical process, including the sequence or partial sequence of a gene, may constitute a patentable invention, even if the structure of that element is identical to that of a natural element.
3. The industrial application of a sequence or a partial sequence of a gene must be disclosed in the patent application."
It should be notes that patentability of genes from other than human sources can be judge using analogy with the human genes, which means that Biotechnology Directive have significant legislation power in this situation.
While the USPTO (United States Patent and Trademark Office) often makes the determination as to whether an invention is non-obvious, the standard is actually set by the Courts and is only applied by the USPTO. The Courts can overrule the USPTO in litigation.
35 U.S.C. Section 103 of the US Patent Act  defines nonobviousness as when:
“…the differences between the subject matter sought to be patented and the prior art are such that the subject matter as a whole would have been obvious at the time the invention was made to a person having ordinary skill in the art to which the subject matter pertains."
US patent law states that the term “invention" means “invention or discovery". However, 35 U.S.C. Section 101 of the US Patent Act  give some clarification
“Whoever invents or discovers any new and useful process, machine, manufacture, or composition of matter ... may obtain a patent therefor ..."
It can be concluded from this fragment that the term 'discovery' is strongly linked to the practical arts, which excludes the patenting of theories, for example. And the word "useful" is also very important in the present context as it prohibit the patenting of anything for which no actual use is evident or studied by the inventor. In practice, consequently, the US law is very similar to the European law, in the definition of what should be excluded from patentability. Using the experience of previous US court cases on DNA patents it can be concluded that it is extremely improbable that US patent law will favor the objection that isolated genes must be categorized as unpatentable discoveries.
Usefulness (in United States patent law); Susceptibility of industrial application (in European patent law).
The Trilateral Project (USPTO, EPO, and JPO)  has studied in detail the patentability of ESTs and DNA fragments. The conclusions that were drawn are:
“1. A mere DNA fragment without indication of a function or specific asserted utility is not a patentable invention.
2. A DNA fragment, of which specific utility, e.g. use as a probe to diagnose a specific disease, is disclosed, is a patentable invention as long as there [are] no other reasons for rejection.
3. A DNA fragment showing no unexpected effect, obtained by conventional method, which is assumed to be part of a certain structural gene based on its high homology with a known DNA encoding protein with a known function, is not a patentable invention (EPO, JPO). The abovementioned DNA fragment is unpatentable if the specification fails to indicate an asserted utility (USPTO).
4. The mere fact that DNA fragments are derived from the same source is not sufficient to meet the requirement for unity of invention."
Additionally, at the trilateral meeting in June 2000 , it was concluded that:
“1. All nucleic acid molecule-related inventions, including full-length cDNAs and SNPs, without indication of function or specific, substantial and credible utility, do not satisfy industrial applicability, enablement or written description requirements.
2. Isolated and purified nucleic acid moleculerelated inventions, including full-length cDNAs and SNPs, of which function or specific, substantial and credible utility is disclosed, which satisfy industrial applicability, enablement, definiteness and written description requirements would be patentable as long as there is no prior art (novelty and inventive step) or other reasons for rejection."
DNA sequences qualify as patentable items because:
the sequences have never before been discovered
even though DNA is found in the body, it isn't obvious
DNA sequences are potentially useful in medicine as diagnostic tools, in finding other sequences, in achieving industrially useful expression products and so on
To get a patent, broadly speaking, inventors must:
identify novel genetic sequences
specify the sequence's product
specify how the product functions in nature – i.e., its use
enable one skilled in the field to use the sequence for its stated purpose
Types of claims 
While a lot of different types of patent can be found for genetic inventions. They can be arranged by three classes regards to the categories of claims used and how the set of claims is structured. It should be noted that not all claims may be present in a single patent; official patent regulations in certain countries may require them to be divided into two or more separate patent applications.
DNA coding for industrially useful expression products.
DNA of specific function and/or nucleotide sequence.
A recombinant vector (plasmid) containing DNA of (1).
A genetically modified organism containing DNA of (1).
A method of production of polypeptide expressed by DNA of (1).
The expressed polypeptide per se (only if novel, i.e. differing in some respect from the naturally occurring protein).
Genes as diagnostic tools.
The wild-type gene of defined nucleotide sequence.
The mutated (altered) forms of the wild-type gene (nucleotide sequences specified).
The DNA primers useful for amplification of the above DNA sequences.
Test method(s) using the above for detecting mutations.
Reagent kits for use with the method(s) of (4).
Screening methodology based on the use of the gene or polypeptide as a target for finding potential therapeutic products.
Genes which control biological pathways. ( this include identification of receptors and genes involved in control of biological pathways and pathogens entry into the cell)
The receptor peptide or polypeptide (protein) of a defined sequence.
DNA coding for the receptor (1).
A transformed cell expressing the receptor (1).
An assay system comprising the transformed cell (3).
A method of identifying an agonist or antagonist of the receptor.
Agonists or antagonists of receptor (1) identified by method (5), (a claim of this type is allowed with great difficulty).
Scope (Broadening Claim Language in Gene Patents) 
As was mentioned previously, the claims define the scope of a patent. There are four general types of claim languages that are used in gene-based patents and patent applications. These languages allowed broadening out the scope of the claim beyond the actual sequences that are disclosed in a specification.
“Hybridisation language in claims allows an applicant to claim a particular nucleotide sequence, as well as any nucleotide sequence that hybridises to that sequences under a given set of experimental conditions." 
Percent Identity Language
“Percent identity language, which is also sometimes expressed as percent similarity language, allows an applicant to claim not only the sequence of interest, but any sequence that is for example, 70, 80, or 90% identical to that sequence." 
There is some significant difficulty with treatise of such type claims, because applicants do not always specify the parameters for calculating the percent identity algorithms. That is why such claims are not often granted these days. Unless examples of related sequences are specified in the patent and furthermore are shown to have similar function, they are not usually allowed.
Amino Acid Substitutions
Amino Acid Substitutions language in claims allows an applicant to claim a particular nucleotide sequence, as well as any nucleotide sequence wherein some amino acid residues are substituted, deleted, added, and/or inserted
Claiming Any Nucleotide Sequence that Encodes a Specified Amino Acid Sequence
“One common way to capture a nucleotide sequence is provide the SEQ ID NO of an amino acid and word the claim such that any nucleotide sequence that encodes that amino acid sequence is claimed. Because the genetic code is degenerate, such a claim encompasses a very large number of nucleic acid sequences." 
Main points (FAQ)
Can different inventors patenting the same DNA strands?
Yeas they can. Sometimes, different inventors can get a patent on the same DNA strands simply because the strands were discovered using different methods. And of course methods themselves can be patented. 
How the issuance of a patent on DNA fragments of a gene will affect the patenting of full-length genes?
The answer can be given using two analogies:
The picture. “The picture tube patent does not preclude someone else from obtaining a patent on a television set. However, the holder of the picture tube patent could sue the television set makers for patent infringement if they use the patented picture tube without obtaining a license." 
“In a second example, a patent might be granted for compound X, which is disclosed to have a specific use (such as a headache remedy). If other investigators find that X has a new and unexpected use, perhaps in combination with compound Y, for treatment of heart arrhythmias, they may have to obtain a license from the individual who first patented compound X in order to sell XY." 
In summary, once a product is patented, that patent extends to any use, even those that have not been disclosed in the patent. A future nonobvious method of using that product may be patentable, but the first patent would have been dominant.
For DNA to be patentable, it must be novel and nonobvious. By this mean that structurally related DNA or RNA information should not be exist in the prior art (in the nonpatent literature or in the prior patents). As was mentioned previously to be considered nonobvious, the invention must have not been obvious “…at the time the invention was made to a person having ordinary skill in the art to which the subject matter pertains". Hence, patent claims limited in scope to a specific novel and nonobvious SNP or EST will not necessarily prevent the future patenting of the corresponding full-length gene of known function, if ,of course, significant amount of information about the gene and/or protein (which can be product of a gene) will be disclosed in the patent application.
Can be patent granted on some sing within patented sequence/gene?
Two specific examples may be helpful:
“A patent is granted to a large fragment of DNA, within which exists a gene of great medical interest, even though the location of the open reading frame with the fragment has not been determined. The person who actually discovers and isolates the gene may also be able to receive a patent" 
“Alternatively, many patented DNA fragments such as ESTs or SNPs may be isolated that turn out to be part of the same gene" 
In both cases, the second patent holder may have to obtain licenses from or pay fees to the primary patent holder but is not prevented from obtaining the second patent. Hence, allowing multiple patents on different parts of the same genome sequence adds extra costs to the researcher who wants to examine the sequence. In this situation the researcher have to pay each patent holder via licensing for the opportunity to study the sequence, and he also has to pay his own staff to research the different patents and determine which are applicable to the area of the genome he wants to study. 
Genetic Testing – Infringement? 
This question is actually failed in two parts:
If laboratory work with the patented isolated genetic sequence, will it infringe the patent?
If laboratory work using the patented method of diagnosis, will it infringe the patent?
And there are two possible answers, depends from the examination of the actual granted patent claims.
First of all, there may be opportunities for inventing around the patent. It is usually permitted when the patent is old and new laboratory or diagnostic methods have been developed (new sequencing technologies, for example).
Second, if a valid gene patent exists, and infringing can be proved, inventor can use some legal defenses. The most relevant defense for the purpose of gene patents and diagnostic testing is the experimental use defense. It is likely that the following activities will fall within the terms of the defense:
research to determine new functions of a patented gene sequence
verifying the functions of a patented gene sequence
finding new SNPs within a patented gene sequence
finding new information related to a gene sequence
research directed at improving a known genetic diagnostic
The research and development of a genetic diagnostic test will most probably fall within the research exception; however the use of research tools, such as Polymerase Chain Reaction (PCR) will require a license. It is very important to notes that once the test has been validated and becomes routine, the use of it will not be an act done for experimental purposes relating to the subject matter of the invention, and will not be covered by the defense.