Females are usually carriers because they only have one copy of the disease allele. Affected males are related through carrier females. For a carrier female, with each pregnancy there is a one in two (50%) chance her sons will inherit the disease allele and a one in two (50%) chance her daughters will be carriers.
A complimentary close, also known as a complimentary closing, is the term prior to your signature in an email message or formal letter. This sign-off phrase shows your respect and appreciation for the person who is considering the request in your letter or email.
State the purpose of your formal letter in the first paragraph and don't veer from the subject. Try to avoid flowery language or long words. Keep the letter short and to the point. This excerpt from Strunk and White's The Elements of Style (4th edition) provides the perfect rule of thumb: Vigorous writing is concise.