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Analysis of sex distribution within families in a large Latin American sample

Mary Furlan Feitosa^I; Henrique Krieger^II

^IDepartamento de Genética, Fundação Oswaldo Cruz, Rio de Janeiro, RJ, Brasil
^IIDepartamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, Cidade Universitária, 05508-900 São Paulo, SP, Brasil. Send correspondence to H.K.

ABSTRACT

A sample of 59,496 Latin American individuals belonging to 28,545 sibships was taken from a large case-control Collaborative Study on Congenital Malformations (ECLAMC). Newborn babies with congenital malformations, and their respective controls, were excluded from the sample in order to avoid biases associated with malformation. On the assumption that Poisson and Markovian effects are not important in determing the overall population distribution of sibships, some statistical models were applied. The general model was a double binomial with one-tail excess. This model can be simplified to a double binomial, a simple binomial with one-tail excess or a simple binomial. The first three distributions fitted the data well (c²₁₅ = 16.46, P = 0.35; c²₁₆ = 20.92, P = 0.18; c²₁₇ = 19.88, P = 0.28), while the simple binomial did not (c²₁₈ = 35.01, P = 0.009). The same models were also applied to several studies carried out in different countries at different times, with similar results. The most parsimonious model that fits most data sets is the double binomial, the results from which suggest that 9% of couples segregate X-linked recessive lethals, since the two segregation proportions of the model are closely in line with the genetic prediction.

Keywords: sex distribution; families; Latin American.

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