Genetic studies in mental subnormality.

Date:
1973
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Genetic studies in mental subnormality. Source: Wellcome Collection.

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    GENETIC STUDIES IN MENTAL SUBNORMALITY The expected number of affected males per sibship = i sA-j-sB Number of affected males _ ^sA = ^A-¡-B Number of affected males s and females This is independent of's' and in all sibships of different sizes the proportion of affected males = i-iA. However, from the present data in 150 sibships: Number of affected males 178 Number of affected males 271 and females = 0-66 — I - ^ A. A = 0-68 and Б =0-32 Therefore it is postulated that in a proportion A (o-68) of sibships males and females would have an equal chance of being affected and in a proportion В (0-32) of sibships only males would be affected. In this and future considera¬ tions, use will be made of the fact that if '/>' is the probability of an affected individual being male and 'ç' the probability of being female so that p-hç = I, then in a proportion A of sibships with 's' affected individuals, these affected individuals will be distributed by sex according to the formula (p-j-ç)'' = i- Sibships with only one affected member There were 60 sibships with only one affected member. Л Expected no. of sibships where males and females would have an equal chance of being affected = о • 68 x 60 — 40 • 8 Expected no. of sibships where only males would be affected =0-32x60 = I9'2 (X^ = 1-44 I degree of freedom, о •30>P>o-20) Sibships with two affected members There were 63 sibships with two affected members. Expected no. of sibships where males and females would have an equal chance of being affected = о • 68 x 63 = 42 • 84 Expected no. of sibships where only males would be affected = о • 32 X 63 = 20 • 16 MM MF FF Total Expected No. (Proportion у4) .. .. io-7i 21-42 iO'7i 42-84 Expected No. (Proportions) .. .. 20-16 — — 20* 16 Total Expected No. .. .. .. .. 30-87 21-42 10-71 63-0 Observed No. .. .. .. .. 33о 19о ii-o 63-0 (^2 = 0-44 2 degrees of freedom o-90>P>o-8o.) Sibships with three affected members There were 23 sibships with three affected members. Expected no. of sibships where males and females would have an equal chance of being affected =0-68x23 = 15-64 Expected no. of sibships where only males would be affected = 0-32 X23 = 7 - 36