Cytogenetic Observations in Infertile Men Working with Insecticidal Compounds

The negative influence of some insecticides on male fertility has been noted. We report our cytogenetic observations on a group of infertile insecticide workers. Increased chromosomal breakage was a constant finding and the Y chromosome was especially damaged. This may account for impaired spermatogenesis. Furthermore, the involvement of heterochromatic chromosomal variants both in the individual susceptibility to the chemically induced damage and in the reproductive fitness is emphasized.

Inbreeding Effects in a Coastal Village and Other Parts of Andhra Pradesh

A survey was carried out among fisher-women in Pallepalam, in Nellore District of Andhra Pradesh, to determine the prevalence and pattern of consanguinity and its effects on fertility, mortality, and morbidity. Of the 106 marriages investigated, 54.72% were consanguineous with predominant proportions of first cousin (36.79%) and uncle-niece (13.21%) marriages. The average inbreeding coefficients for autosomal and sex-linked genes were found to be 0.0405 and 0.0448 respectively. The differences between consanguineous and nonconsanguineous marriages were studied with respect to fertility, mortality and morbidity.

Bibliography on Prenatal and Natal Influences in Twins

The author agrees with earlier writers that most of the differences observed in monozygotic pairs are due to unusual or extreme environmental factors acting before or during the twins' birth. Although they are typical of development in twins, these environmental factors can hardly be considered typical of development in other individuals. This point, as a review of the literature shows, is often overlooked by those who study twins in the childhood or adult age ranges. As a result the inferences drawn from twin differences are frequently mistaken, or at least quite exaggerated so far as the significance of postnatal influences in non-twins is concerned. At the same tihe, if allowance is made for the environmental biases peculiar to twin studies, the findings may be said to establish more about the importance of heredity in the medical and behavior sciences than most investigators have thought. In the author's opinion the largest single source of bias is the mutual circulation that exists during prenatal development of the majority of monozygotic pairs. Data on that circulation's difference-producing effects are reviewed and related to studies of mature twins. Effects of lateral inversions (asymmetry reversals) and of “natal” factors (chiefly conditions of delivery) are also reviewed, and methods of judging the importance of all three of the biasing conditions are outlined. Need for obtaining systematic and complete information about the natal factors is stressed.

Heritability Estimates from Twin Studies. I. Formulae of Heritability Estimates

Over the past 50 years a large number of methods have been proposed for estimating heritability from twin studies. The present paper describes the most commonly cited of these estimates as a first step in evaluating their usefulness. A critical review will then follow.

Double Trisomy as a Mosaic. Case History (48,XYY,+21/47,XY,+21) and Survey of the Literature of Mixed Autosomal-Gonosomal Trisomies

The case of a boy is reported showing the typical symptoms of Down's syndrome, in whom the chromosome analysis revealed a mosaic karyotype: 50% 48,XYY,+21/50% 47,XY,+2l. Findings of 92 cases from the literature are summarized to show the frequencies of double gonosome-autosome aneuploidies compared with single trisomies. Referring to the different chromosomes involved, the aneuploid cell formation, the frequencies of combinations, as well as the tendency to mosaic formation are analyzed. The age of parents at the time of birth and the life expectancy are described as well as the clinical symptoms. Theories concerning the origin of double aneuploidies are discussed.