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Changing gender is one of the important subjects, which is of great significance in medicine and law. Although, these subjects were existed in the past, owing to the development of technology and medical science, it has recently improved a lot. Nowadays, according to the view of Islamic Jurisprudents and in the most legal systems, this action will be quite lawful provided that the doctors recognize its effects of this action should be considered. One of these effects would be the relationship of couples with each other. For instance, does the contract of marriage will be remind or cancelled? What will happen to the dower (the money that hausband is obliged to give to his wife)? What about the waiting period (Iddah), inheritance, guardianship, custody and…. Generally, in a contract that the kind of gender has not role, changing gender has no effect. But, in a contract that the kind of gender play a fundamental role, it will be cancelled from the moment that it has been changed, and does not have any effect on the previous acquired rights.

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   The Contract of Sale as one of the most exchanged contracts requires each parties to perform The Obligations against the other Party. According to the Vienna Convention, the Seller is required to perform the Obligations against the Buyer. The question is that whether Usage is effective in determining of The Obligations of the Seller based on the Convention on the International Sale of Goods? Parties to the contract are not required to predict and specify all details of the contract, It is sufficient to reach an agreement on the elements of the subject matter of the contract and Usage and Supplementary law determine other details and the effects of contract (specifying the rights and obligations of the parties about it). Article 220 and 225 of the Civil Code confirms this claim. Usage also have an important role based on the Vienna Convention 1980, because, in the Convention on the International Sale, in addition to being, the parties are bound by any usage to which they have agreed and by any practices which they have established between themselves, are considered, unless otherwise agreed, to have impliedly made applicable to their contract or its formation a usage of which the parties knew or ought to have known and which in international trade is widely known to, and regularly observed by, parties to contracts of the type involved in the particular trade concerned. In this Research will examine the effect of Usage and Practice in determining the Obligations of the Seller. By induction under the provisions of the Convention, we get the general result  that, in the assumption of the absence of an agreement on the determination of sellers obligations, according to Article 9 of the Convention, Usage and Practice will undoubtedly determine the sellers obligations.Therefore, in the absence of an agreement between the parties on the commitment to certain Usages and the lack of Practice among them regarding the Sellers obligations, if the conditions of the Usages referred to in paragraph 2 of Article 9 of the Convention exist, the seller will be obliged to comply with it. Finally, in the absence of decisive rules, the Seller is bound to fulfill its obligations, In accordance with the Supplementary Provisions of the Convention. The same situation exists in the Iranian law.
 

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The Islamic religion is a global phenomenon and keeps expanding rapidly. Muslim law, like personal laws of other religious groups, is today facing several challenges from within the community as well as from outside. This is but natural in an era of unprecedented changes in societies everywhere. As a matter of fact, Islamic law like any other law is in need of reform. The urgency lies in the application of contemporary standards of principle of legality, equality, dignity and individual rights in matters relating to criminal law and marriage, divorce, inheritance, guardianship, maintenance and other social contemporary problems.  Although religious scholars effectively terminated the practice of ijtihad five hundred years ago, the principles of interpretation are well established and hence; the need for contemporary interpretation is compelling. The practice of the Companions, the Successors and the leading Mujtahidun of the past tends to suggest that they enacted laws and took measures in pursuance of maslahah (issues) despite the lack of textual authority to validate them. Egypt is often taken as an example for a distinctively Islam nation and in the Western world it is often assumed that its legislation is based on Islamic principles.  In recent years, the Iranian system has established the Exigency Council to resolve conflict between bodies like the Guardian Council and the Islamic Consultative Assembly, with regard to Islamic and criminal law's contemporary issues.