Sib - Sib Marriages in
the Egyptian Dynasties
Full sibs have a relatedness r = 1/2, and their offspring have
an inbreeding coefficient
F = 1/4. This means they are identical by descent
at one-quarter of their loci. If any of these loci
involve recessive homozygotes that affect pre- or
perinatal health (especially, novel mutations to
deleterious or lethal alleles), delays to time of
offspring and mortality rates of such children will
be higher then those from marriages between unrelated persons. The
expectation of reduced health of inbred offspring of such
marriages is called inbreeding
depression.
In most societies, the consequences of
inbreeding depression are recognized and discouraged or prohibited
by taboos against close marriages, sometimes including First
Cousins. In others, including Egyptian dynasties [above]
and Native Hawai'ian royal families, marriages between
close relatives were encouraged as a means of preserving power.
Homework:
Identify the number and type of consanguineous
marriages in the above pedigree. Recall the convention that
consanguineous marriages are indicated by double lines.