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PubMed1994

The costs of human inbreeding and their implications for variations at the DNA level.

An analysis of the world literature on the children of first cousin marriages reveals that the depression of survival in offspring followed from birth (including late miscarriages; at about six months gestation or later) to a median age of 10 years is constant (4.4% +/- 4.6) across a wide range of values for population prereproductive mortality. There is thus no evidence for the action of conditional lethals. On the basis of these data, it is calculated that the average human is heterozygous for only 1.4 lethal equivalents capable of acting over this portion of the life cycle. The implications of these results are discussed in the context of genetic counseling, and the biomedical significance of variation in DNA.

Adolescent↗
PubMed1978

Effect of inbreeding on IQ and mental retardation.

Both decline of IQ and increase of mental retardation are consistent with rare recessive alleles at about 325 loci. There is no suggestion of a discrepancy that might be due to polygenic dominance or confounding of consanguinity with unfavorable environment. These data indicate that the risk for mental retardation in matings of normal parents increases from 0.012 with random mating to 0.062 for first-cousin parentage but that dominance deviations are a negligible cause of family resemblance of IQ. Implications for frequencies, mutation rates, and radiation response are detailed.

Consanguinity↗
PubMed1996

How flowering plants discriminate between self and non-self pollen to prevent inbreeding.

Flowering plants have evolved various genetic mechanisms to circumvent the tendency for self-fertilization created by the close proximity of male and female reproductive organs in a bisexual flower. One such mechanism is gametophytic self-incompatibility, which allows the female reproductive organ, the pistil, to distinguish between self pollen and non-self pollen; self pollen is rejected, whereas non-self pollen is accepted for fertilization. The Solanaceae family has been used as a model to study the molecular and biochemical basis of self/non-self-recognition and self-rejection. Discrimination of self and non-self pollen by the pistil is controlled by a single polymorphic locus, the S locus. The protein products of S alleles in the pistil, S proteins, were initially identified based on their cosegregation with S alleles. S proteins have recently been shown to indeed control the ability of the pistil to recognize and reject self pollen. S proteins are also RNases, and the RNase activity has been shown to be essential for rejection of self pollen, suggesting that the biochemical mechanism of self-rejection involves the cytotoxic action of the RNase activity. S proteins contain various numbers of N-linked glycans, but the carbohydrate moiety has been shown not to be required for the function of S proteins, suggesting that the S allele specificity determinant of S proteins lies in the amino acid sequence. The male component in self-incompatibility interactions, the pollen S gene, has not yet been identified. The possible nature of the pollen S gene product and the possible mechanism by which allele-specific rejection of pollen is accomplished are discussed.

Alleles↗
PubMedDate not supplied

Inbreeding and fertility in a South Indian population.

Among 1913 women in Karnataka State, South India, 37.74% had married a relative (a consanguineous union), 60.79% were non-consanguineously married, and 1.46% did not know whether they had married a relative. Mean number of living offspring for consanguineously married women who had completed their reproduction was 3.89, and for the non-consanguineous 4.07. There is no significant difference in the mean level of fertility for the two groups measured in this way. Pre-natal mortality is lower (but not significantly) among consanguineously married women who have completed their reproduction than among the non-consanguineous group, but post-natal mortality is significantly higher among the conceptuses of the consanguineously married women. Although consanguineously married women conceive more frequently, that is, are more fecund than the non-consanguineous women (mean number of conceptions being 6.61 and 6.28, respectively), the difference is not significant. The differential survival of the offspring results in the consanguineous group having slightly lower net fertility, although the difference is not statistically significant. The lower sterility rates of the consanguineously married women (3.21% of all consanguineously married women show primary sterility compared to 3.47% of the non-consanguineous) may be due to greater compatibility of uniting gametes in the consanguineous marriages. The data reveal that women married to a relative and having completed their reproduction show higher fecundity, lower pre-natal mortality, higher post-natal mortality, lower sterility rates, and thus no significant difference in net fertility to those who had not married a relative.

Adolescent↗