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Results for “Sex Ratio--statistics”

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At least 19 recordsLinked to original sources
PubMed1985

Fetal mortality in sibships with one or more affected members with oral clefts.

We investigated the fetal mortality in 903 sibships with at least one member having cleft lip with or without cleft palate [CL(P)] and 213 with at least one individual affected with cleft palate (CP) derived from three different data sources in México. The frequency of fetal wastage (abortion and/or stillbirth) was not increased in sibships where the propositi had cleft lip and palate (CLP) as compared with cleft lip (CL) nor in those where index cases had a bilateral lesion as compared to a unilateral one, nor when the index cases with CL(P) were female rather than males, nor when the index case was a female with bilateral lesion as compared to males with a unilateral one. Similarly fetal mortality was not increased in sibships in which the propositus had CP compared to those in which the index case was a female. These findings are contrary to some reports that claim to support a two-threshold model according to which individuals reaching the first one would be born with an oral cleft, and those reaching the second would be aborted. Our results, together with others, suggest the possibility that liability to oral clefts is independent of liability to fetal wastage.

Abortion, Spontaneous↗
PubMed1989

Genetic analysis of the cause of exencephaly in the SELH/Bc mouse stock.

A new mouse stock, SELH/Bc, having a high liability to exencephaly has been developed. About 17% of SELH fetuses are exencephalic. The genetic cause of this exencephaly was investigated in a cross to a normal related ICR/Bc strain and in subsequent classical genetic crosses (F2, first and second backcrosses). The data were compared with a number of genetic models, including that of a single recessive mutation with 17% penetrance. The data did not fit single-locus inheritance. The expectations from the multifactorial threshold model based on an underlying quantitative liability trait with additive inheritance were found to fit the data very well. The number of loci involved was estimated to be about two or three. About 70% of exencephalic SELH fetuses are female, and there is no overall deficiency of males. The relatively higher risk in females was constant across the genetic backgrounds in the experiment. In summary, the liability to exencephaly in SELH mice appears to be a multifactorial threshold trait, and it therefore resembles human neural tube defects in type of genetic etiology. SELH therefore may be a valuable animal model in the study of neural tube defects.

Animals↗
PubMed1984

On the optimal sex-ratio: a stability analysis based on a characterization for one-locus multiallele viability models.

Theoretical one-locus multiallele sex-determination models are found to admit even sex ratio equilibrium surfaces besides the equilibria for corresponding one-locus multiallele viability models. Both types of equilibria can be defined in terms of a single spectral radius function, the former corresponding to level surfaces and the latter to critical points. The stable equilibria in the corresponding viability models are associated with the local maxima, and the equilibrium structures for the sex-determination models can be fully described. Several optimality properties of the even-sex-ratio equilibrium surfaces can be deduced.

Alleles↗
PubMed1992

Population studies of INV(9) chromosomes in 4,300 Japanese: incidence, sex difference and clinical significance.

Population incidence of a chromosome 9 with an inversion of qh, inv(9), was surveyed using C-banding in a total of 4,367 Japanese which consisted of five patient groups and a normal control group. The inv(9) incidence was 1.65% in the normal control group (n = 1,513) and 1.52% in the Down syndrome patient group (n = 1,246). The incidence of female carriers was 1.7 times higher than that of male carriers in the above two groups. The sex difference was significant (p < 0.05). Moreover, the incidence in the 47,XXY male group (n = 277) was slightly higher than female carrier incidences. The excess of carriers about 2 times was observed in the habitual abortion couple group (n = 694) and the spontaneous abortus group (n = 181), both having normal karyotypes. The present data probably indicate the existence of a genetic effect of inv(9) on human reproductive performance, while they could not explain the sex difference found in inv(9) carriers. Our speculation for the sex difference has been presented.

Abortion, Habitual↗
PubMed1986

Hierarchical selection theory and sex ratios. I. General solutions for structured populations.

Models of sex-ratio evolution in structured populations are derived with G.R. Price's covariance form for the hierarchical analysis of natural selection (1970, Nature 227, 520-521). Previous work on competition among related males for mates (local mate competition), competition among related females for a limiting resource (local resource competition), inbreeding, group selection, and asymmetry of genetic inheritance between males and females, are subsumed under a general formulation for sex-ratio biases in structured populations. I found that the evolutionarily stable strategy sex ratio (males:females) for diploids is 1 - rho m:1 - rho f, where rho m is the regression coefficient of relatedness of the controlling genotypes on males competing for mates, rho f is the regression of controlling genotypes on females that compete for a fixed, limiting resource, and there is no inbreeding. For inbreeding and no competition among females, the evolutionarily stable strategy is 1 - rho m:1 + rho mf, where rho mf is the regression of controlling genotypes on females' mates.

Animals↗
PubMed1986

The two-sex multiethnic stable population model.

A two-sex multiethnic stable population is a model with fixed mortality and fertility parameters that explicitly recognizes the behavior of males and females in at least two distinct ethnic groups. The presence of intergroup fertility may allow the different ethnic groups to grow at a constant rate in a population with a fixed sex-ethnic composition. The present paper considers a variety of rules for determining the ethnicity of intergroup births based on the ethnicities of the mother and father, and examines the mathematical models implied by those rules. Numerical examples are presented for a two-ethnic-group population in cases where intergroup births are shared equally by the two groups, are all considered members of one particular group, and are all members of the father's group. A special case of a more general model, where sons become members of the father's group and daughters become members of the mother's group, is also considered. The results suggest that when intergroup fertility is not uncommon, how ethnicity is determined can substantially influence the ethnic composition of the population.

Ethnicity↗
PubMed1987

The monozygotic twinning rate: is it really constant?

Weinberg's difference method, applied to twin birth statistics, usually shows a dependence of the MZ rate on maternal age, like a thin shadow of the DZ rate. Some of this MZ variation could be explained away by James' finding of more same-sex (SS) than opposite-sex (OS) DZ twins, the excess being mistakenly classified as MZ by Weinberg's assumption of equal numbers. By several methods one can extract a constant value for the MZ rate and a constant or nearly constant value for the DZ SS/OS ratio, but these "constants" are actually arbitrary and they vary between populations.

Birth Order↗
PubMed1975

Sex ratio in twin births.

1. Data on more than 2 1/2 million twin births suggest that the regression of sex ratio in twins on maternal age does not decline monotonically like that of singletons, but, like the incidence of dizygotic twinning, seems to rise and then fall with maternal age. 2. Accordingly it is hypothesized that the sex ratio in monozygotic twins is lower than that in dizygotic twins or that in singletons. This would account also for the low overall sex ratio in twins. 3. The data are consistent with the hypotheses that the monozygotic twin sex ratio is constant for all maternal ages at a value of about 0.496, and that the dizygotic twin maternal age-specific sex ratios are the same as the singleton sex ratios for the same maternal ages. 4. The hypothesized low sex ratio in monozygotic twins is reminiscent of that in some congenital malformations: possibly some aetiological factor is common to monzygotic twins and such congenital malformations. 5. It is suggested that the total-birth sex ratio of triplets is underestimated in national vital statistics records.

Female↗
PubMedDate not supplied

Maternal factors in dizygotic twinning: evidence from interracial crosses.

In the USA, Blacks have been shown to have a higher incidence of DZ twinning than Whites. We studied maternal and paternal race determinants of the rates of like-sex and unlike-sex twinning using US live-birth certificate data for 1973-78. After adjustment was made for father's race, Black mothers had a higher rate of unlike-sex twinning than White mothers (odds ratio, OR = 1.74, P less than 10(-8]. This maternal race effect persisted after further adjustments were made for maternal age, parity, education, and marital status and did not apply to the rates of like-sex twinning (OR = 1.06). On the other hand, after adjustment was made for mother's race, Black fathers did not have higher rates of unlike-sex (OR = 0.93) or like-sex (OR = 1.11) twinning than White fathers. The study shows that the high rate of DZ twinning in Blacks is associated with maternal race and not paternal race. The data further support the importance of maternal determinants of dizygotic twinning in humans.

Black People↗