SEPTEMBER 2006 (updated February 2015)

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 in the introduction 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.



This monograph is mainly concerned with the classification, graphic representation, measurement and coding of human relationships. It also explains the significance and harmful consequences of inbreeding. Other aspects of genealogy included are: generation intervals, legal constraints on the marriage of relatives and present rules for the inheritance of property.




Acceptable and non-acceptable levels of inbreeding

The effects of inbreeding on the children of cousin marriages

Removed Cousins

Longevity and generation intervals

The ancestor paradox

The direct relationship paradox

Calculation of the coefficient of relationship (R) for sex-linked genes

Calculation of the coefficient of inbreeding (F) for sex-linked genes

Case histories of intestate wills

Extension of coding for relationships

Calculating the coefficient of inbreeding by coancestry

Direct Relationships

Non Genetic Relationships

Three-quarter Sibs

Examples of unusual relationships and genealogical rarities


List of Tables

Table 1 Acceptable and non-acceptable levels of inbreeding in human populations

Table 2 Coefficients of relationship between various degrees of cousins

Table 3 Proportion of homozygous recessive individuals in children from cousin marriages compared with those expected in a random-mating population, for different gene frequencies

Table 4 The effect of a first cousin marriage on the probability that the first great-grandson of an albino will inherit the same condition

Table 5 Removed cousins and other intergeneration collateral relationships

Table 6 Coefficients of relationship when all the genes are either sex-linked or autosomal

Table 7 F values of female progeny for sex-linked genes

Table 8 Incidence of sex-linked colour blindness

Table 9 Incidence of haemophilia

Table 10 Coding for non-reciprocal intergeneration doubles (regular)

Table 11 Coding for non-reciprocal intergeneration doubles (irregular)

Table 12 Coding for enhanced half sib doubles(all irregular)

Table 13 Coding for reciprocal cross - gneration double relatives

Table 14 Coding for double relationships caused by inbreeding

List of Figures

Figure 1 Four generation pedigree

Figure 2 Five generation pedigree

Figure 3 Six generation pedigree

Figure 4 Diagram showing loss of ancestors caused by a first cousin marriage

Figure 5 Broken male line

Figure 6 Y chromosome and mitochondrial inheritance

Figure 7 Parent and child relationships for sex-linked genes

Figure 8 Full sib relationships for sex-linked genes

Figure 9 Paternal half sib relationships for sex-linked genes

Figure 10 Maternal half sib relationships for sex-linked genes

Figure 11 Paternal uncle and aunt relationships for sex-linked genes

Figure 12 Maternal uncle and aunt relationships for sex-linked genes

Figure 13 Patrilateral ortho-cousins

Figure 14 Matrilateral ortho-cousins

Figure 15 Patrilateral cross-cousins

Figure 16 Matrilateral cross-cousins

Figure 17 First and second cousins

Figure 18 Basic Formula

Figure 19 Modified diagram for full sibs

Figure 20 Modified diagram for half sibs

Figure 21 First cousin marriages

Figure 22 Uncle-niece marriages

Figure 23 Double first cousin marriage

Figure 24 Close inbreeding (full sibs)

Figure 25 Stylised Representation of Branching Direct Lines

Figure 26 General Representation of Direct Relationships

Figure 27 Single Direct Relationships

Figure 28 Regular Double Direct Relationships

Figure 29 Regular Multiple Direct Relationship

Figure 30 Octuple Great Great Grandfather(Three generations of full sib mating.)

Figure 31 John of Gaunt to Margaret Tudor (R = 0.0624)

Figure 32 Queen Victoria to Prince Charles (R = 0.0624)

Figure 33 Irregular Double Grandparent

Figure 34 Irregular Double Great Grandparent

Figure 35 Irregular Multiple Direct Relationship

Figure 36 Edward III to Richard (Duke of York) (R = 0.1556)

Figure 37 George III to George VI (R = 0.0934)

Figure 38 Edward III to James V of Scotland (R = 0.0331)

Figure 39 Close Inbreeding (Incest)

Figure 40 Mild Inbreeding

Figure 41 Single Direct Relationships (All Unilineal)

Figure 42 Double Grandparent - Grandchild (Bilineal Only)

Figure 43 Unilineal Double Direct Relationships

Figure 44 Further Bilineal Double Direct Relationships

Figure 45 Unilineal Multiple Direct Relationships

Figure 46 Bilineal Multiple Direct Relationships

Figure 47 Variant Form of Double Half First Cousins (Unilineal)

Figure 48 Conventional Double Half First Cousins (Bilineal)

Figure 49 Male, Female and Mixed Direct Lines

Figure 50 TheSaxons (8 generations - 16 kings)

Figure 51 The Plantagenets (11 generations - 14 kings)

Figure 52 The Scottish Stuarts (7 generations - 7 kings))

Figure 53 House of Hanover (5 generations - 5 kings)

Figure 54 House of Saxe-Coburg-Gotha/Windsor (3 generations - 4 kings)

Figure 55 Diagrammatic Representation of Sex Chromosomes in Birds and Mammals

Figure 56 Father - Daughter Incest

Figure 57 Grandfather - Granddaughter Incest

Figure 58 Brother-in-law

Figure 59 Sister-in-law

Figure 60 Uncle-in-law

Figure 61 Aunt-in-law

Figure 62 Nephew-in-law

Figure 63 Niece-in-law

Figure 64 Father-in-law and Son-in-law

Figure 65 Mother-in-law and Daughter-in-law

Figure 66 Grandfather-in-law and Grandson-in-law

Figure 67 Grandmother-in-law and Granddaughter-in-law

Figure 68 Stepfather and Stepmother

Figure 69 Stepson and Stepdaughter

Figure 70 Stepgrandfather and Stepgrandmother

Figure 71 Stepgrandson and Stepgranddaughter

Figure 72 Stepfathers and Stepmothers

Figure 73 Stepsons and Stepdaughters

Figure 74 Stepgrandfathers and Stepgrandmothers

Figure 75 Stepgrandsons and Stepgranddaughters

Figure 76 Stepbrother and Stepsister

Figure 77 Serial Marriages

Figure 78 Serial Marriages to the Same Person

Figure 79 Stepuncle and Stepaunt

Figure 80 Stepnephew and Stepniece

lass=MsoTof > Figure 81 Marriage to Father-in-law

Figure 82 Marriage to Sister-in-law

Figure 83 Marriage to Niece-in-law

Figure 84 Marriage to Grandfather-in-law (Husband's Grandfather)

Figure 85 Marriage to Stepmother

Figure 86 Marriage to Stepsister

Figure 87 Marriage to Father-in-law

Figure 88 Marriage to Mother-in-law

Figure 89 Marriage to Son-in-law

Figure 90 Marriage to Daughter-in-law