"Генеалогические" и "случайные" совпадения сегментов хромосом

[I2a1a]

Expected distributions of IBD chromosomal segments between pairs of
individuals.
(A) The process underlying the pattern of IBD segments. Two homologous
autosomal chromosomes are shown for two parents, each colored differently. Meiosis and
recombination occurs and two sibling offspring inherit recombinant chromosomes (just
one crossover per homologous pair for each meiosis event is depicted, marked by an ‘X’).
For some segments of the chromosome in question, the siblings share a stretch that was
inherited from one of the four parental chromosomes. The three IBD segments are
identifiable as regions that share the same color (boxed and marked at right by black
bars). The siblings mate with unrelated individuals and the offspring each inherit an
unrelated chromosome (tan or gray) and one that is a recombinant patchwork of the
grandparental chromosomes. These first cousins share one segment IBD at this
chromosome (red, boxed).


(B) The number of segments that a pair of individuals shares
IBD, across all chromosomes, is approximately Poisson distributed with a mean that
depends on the degree of relationship d between the individuals (d = 2, 4, 6, 8,
corresponding to siblings through third cousins).

(C) The lengths of the IBD segments are
approximately exponentially distributed, with mean length depending on the relationship
between individuals (theoretical distributions shown for d = 2d, 4th, 6th, 8th cousins).

[I2a1a]

Characteristics of HapMap CEU parents as a background reference
population.

......


(B) Distribution of the number of segments with length > 2.5 cM that are inferred to be shared IBD by GERMLINE in pairs of CEU individuals (Observed), with fitted Poisson distribution (Expected).

(C) Distribution of the lengths of IBD segments longer than 2.5 cM in CEU pairs (Observed), with fitted exponential distribution (Expected).

(D) Scatterplot of the number of IBD segments per pair vs. mean length of segments in the pair.