The main purpose of the following supplement is to anticipate and answer those questions most frequently asked about the genetic and quantitative aspects of genealogy and relationships. A secondary aim is to enlarge on certain specialised topics, which were only briefly covered in the monograph, but which may be of further interest. The following sections, which are summarised below, give more information in both these areas. However, I would like to stress that my specialist subject is genetics and that any complicated enquiries related to marriage laws and intestate wills should be addressed to a qualified legal expert.
Many people are concerned about which relatives they can legally marry and whether their children will be affected by inbreeding. I have taken a second look at these two areas. Identification of the various kinds of cousins, particularly those that are several times removed, can also cause problems, and is discussed in detail. The subject of average life span is examined, together with the effects of longevity on generation intervals; and the implications of older parents having children.
Other topics covered include the two apparent paradoxes about ancestors and descendants and the peculiar effects of sex-linked inheritance on measures of relationship and inbreeding. The case histories of several intestate situations are outlined, to emphasise that the outcome may not be what the deceased intended, and therefore the importance of making a will.
To illustrate the versatility of the previous coding system for relationships, the code has been extended to accommodate some of the less common situations omitted from the original list. Finally, to show the human aspect of the more unusual relationships and marriages, I have included a list of examples, some of which are documented, and others (anonymously) from my own family and colleagues. This is not complete and I would welcome information on further cases, and also on any obscure relationships I may have overlooked, and any errors that have crept in. Added at a later date (2012) are two further sections on Direct Relationships and Non-genetic Family Relationships.