Errors in the Elimination of X Chromosomes in SCIARA OCELLARIS

It was previously assumed that the X-linked recessive mutation, sepia, induced errors in X-chromosome elimination during early embryogenesis of Sciara ocellaris. The results obtained in the present analysis corroborate this assumption and permit a further classification of the type of error this mutation induces. Among 85,244 individuals analyzed, three kinds of aberrant flies were identified: mosaics (0.01%), gynandromorphs (0.42%) and phenotypically exceptional individuals (0.25%). The origin of these abnormal flies could be ascribed to errors in selective elimination of X chromosomes that occur in male meiosis or during the early cleavages of the zygote nuclei. This last kind of error could be classified into three types: (a) error in number, (b) error in type, and (c) error in number and type of X chromosome eliminated. Evidence is provided indicating that sepia has no direct effect on the X chromosome; it has a maternal influence and exerts its effect only in the heterozygous condition.     

Semidominant effect of the l(1)ts403 (sbr10) mutation on nondisjunction of sex chromosomes in meiosis in Drosophila melanogaster females exposed to heat

The sbr gene of Drosophila melanogaster belongs to the NXF (nuclear export factor) family responsible for the mRNA transport from nucleus to cytoplasm. We have shown that in the heat-exposed (37 degrees C, 1 h) females, the l(1)ts403 (sbr10) mutation leads, in particular, to the high-frequency nondisjunction and loss of sex chromosomes in meiosis. For this trait, the incomplete dominance of the sbr10 mutation is observed. At the same time, the sbr10 mutation is recessive for many other traits of the heat-exposed flies: reduced viability, low fertility, impaired synthesis of the heat shock proteins, etc. The females heterozygous for the null allele (Df(1)vL4, a deletion eliminating gene srb) do not differ from females homozygous for the wild-type allele in frequency of the heat shock-induced nondisjunction and loss of sex chromosomes in meiosis. Because of this, the sbr10 mutation can be assigned to the gain-of-function alleles (those gaining the dominance function). Expression of the mutant sbr10 allele against the background of the wild-type allele suggests that in the heat shock-exposed females, the heat-modified product of this ts allele has a strong effect on sex chromosome disjunction in meiosis.     

Behavior of gynandromorphs of the wasp Habrobracon juglandis.

A study was made of sex behavior for 276 gynandromorphs of the wasp Habrobracon juglandis. In general, gynandromorphs with male heads behaved like males, those with female heads behaved like females, and those with mosaic heads as either male or female or both. These observations corroborate those made by P. W. Whiting in 1932 and confirm his view that the site of sex behavior is in the brain. Correlations between sex behavior and the sex of various body structures showed clearly that sex behavior is unrelated to the thorax, abdomen and genitalia. The sex behavior of gynandromorphs does not seem to be related to the sex of the external sensors of the head but rather to the genotype of the brain.     

Semidominant Effect of the l(1)ts403 (sbr 10) Mutation on Sex Chromosome Nondsjunction in Meiosis in Drosophila melanogaster Females Exposed to Heat

The sbrgene of Drosophila melanogasterbelongs to the NXF(nuclear export factor) family responsible for the mRNA transport from nucleus to cytoplasm. We have shown that in the heat-exposed (37°C, 1 h) females, the l(1)ts403(sbr ¹⁰) mutation leads, in particular, to the high-frequency nondisjunction and loss of sex chromosomes in meiosis. For this trait, the incomplete dominance of the sbr ¹⁰ mutation is observed. At the same time, the sbr ¹⁰ mutation is recessive for many other traits of the heat-exposed flies: reduced viability, low fertility, impaired synthesis of the heat shock proteins, etc. The females heterozygous for the null allele (Df(1)v ^L4, a deletion eliminating gene srb) do not differ from females homozygous for the wild-type allele in frequency of the heat shock-induced nondisjunction and loss of sex chromosomes in meiosis. Because of this, the sbr ¹⁰ mutation can be assigned to the gain-of-function alleles (those gaining the dominance function). Expression of the mutant sbr ¹⁰ allele against the background of the wild-type allele suggests that in the heat shock-exposed females, the heat-modified product of this ts allele has an active effect on sex chromosome disjunction in meiosis.     

New sex-linked mutation of wings fragility with age-depended expression (<Emphasis Type="Italic">fw</Emphasis>) in <Emphasis Type="Italic">Musca domestica</Emphasis> L.

A mutation of wing fragility that was not yet been revealed in adult housefly is described. Criss-cross inheritance of the character of fragility of the wing blade, which indicates localization of gene (fw) for this character in the X chromosome. Phenotypic expression of the mutant allele depends on sex. In male flies, the mutant allele in hemizygous state is expressed at the age of 2–3 weeks and older with penetrance close to 100%. In females, the mutant allele in homozygous state is lethal and in heterozygous state, totally recessive.     

Control of Female Reproduction in Drosophila: Genetic Dissection Using Gynandromorphs

The sexual behavior of Drosophila melanogaster gynandromorphs was studied to analyze the relationship between different steps in the female reproductive pathway. It was assumed that, in some gynandromorphs, certain female functions are missing because the corresponding control sites (foci) are either composed of male tissue or did not develop. A given gynandromorph can show elements of both male and female reproductive pathways. None of the steps of the female reproductive pathway appeared to be dependent on any other, in contrast to male behavior where, for example, following of females is a prerequisite for attempted copulation. By correlating each of the behaviors with the genotype of the cuticle, we confirmed previous findings that the focus for the female sex appeal is located in the abdomen, but receptivity to copulation is controlled by a site in the head. Many of the gynandromorphs did not lay eggs, presumably because either the focus controlling egg transfer from the ovaries to the uterus or the one controlling egg deposition was composed of male tissue. Many of the nonovipositing gynandromorphs laid eggs while dying or could be induced to deposit eggs after implantation of hormone-producing glands or topical application of a juvenile hormone analog. Some of the noninseminated gynandromorphs laid eggs at the rate characteristic for inseminated females, suggesting that an oviposition focus (mapping in the head region) suppresses oviposition in virgin females, but not in gynandromorphs whose focus is composed of male tissue. Some of the inseminated gynandromorphs oviposited eggs at a low rate, possibly because the focus responsible for detection of insemination could not function properly. Some of the inseminated gynandromorphs laid unfertilized eggs, revealing the importance of the focus controlling sperm release from the seminal receptacle. Foci controlling egg transfer, egg deposition and sperm release are located in the thorax, according to mosaic fate mapping results and studies on the reproductive behavior of decapitated females. The location of egg deposition in the culture vial seems to be controlled by a brain site. Sexual behavior in Drosophila does not depend on the presence (or absence) of the ovary or germ line.     

Mating success of wild type and sepia mutants Drosophila melanogaster in different choice.

Mating behaviour of red-eyed (wt) and brown-eyed (sepia) Drosophila melanogaster was studied under light conditions. Mating success was directly observed in mating vials and techniques usually applied in the studies of sexual selection ("female choice" and "multiple choice"). The comparison of sexual activity of mutant and wild types clearly indicates that they are not equally successful in matings. Sepia eye colour mutation decreases sexual activity of Drosophila melanogaster males, influences the preference ability of females and decreases the number of progeny from homogamic mating of the se x se type, as well as from heterogamic copulations in which sepia females take part. Non-random mating of wild type males and sepia females (in "multiple-choice" situation), with genetically and phenotypically different individuals, could be another mechanism for conservation of genetic polymorphism in natural populations.     

Cultural inheritance of the desire for male offspring and the incidence of a sex‐linked lethal disease

Abstract

This paper studies the effect of having at least one male offspring on a sex‐linked recessive disease and the fraction of affected males due to fresh mutations. The equilibrium frequency of heterozygous females depends not only on the intensity of the reproductive compensation, but also on the time of mutational change. It has been shown that the frequency ranges from 4u without reproductive compensation to √2u or √3u with strict compensation, where u is the mutation rate from the wild type allele to lethal gene. The frequency √2u is achieved when mutation occurs in mature germ cells, whereas, √3u achieved when mutation occurs in early development of germ cells. This increased frequency of heterozygous females due to reproductive compensation reduces considerably the proportion of affected males due to fresh mutation.     

The use of compound heterozygotes and Hprt selection to analyze X-linked mottled alleles associated with prenatal lethality

X-linked mutant alleles associated with prenatal male lethality are difficult to analyze because only heterozygous females are readily available for study. Genomic analysis of the mutant allele is facilitated by the construction of somatic cell hybrids because this enables the segregation of the X Chromosomes (Chrs) that carry the mutant and wild-type alleles. We describe here a method that ensures that the X Chr carrying the mutant allele is retained in somatic cell hybrids in an active selectable state. This is achieved by mating heterozygous females to males that carry a mutation at the hypoxanthine phosphoribosyl transferase (Hprt) locus. The resultant F₁ females are compound heterozygotes, and when cells from these females are fused to HPRT− Chinese hamster cells and subjected to selection in HAT medium, the only survivors are those hybrid cells that retain an active X Chr carrying the mutant allele together with the wild-type Hprt allele. We use hybrids constructed by this method to demonstrate that there are no gross deletions or genomic rearrangements present in three mottled alleles associated with prenatal male lethality. Received: 8 January 1996 / Accepted: 29 February 1996     

Sex Differences in Polymorphism and Expression of AAT-1 in the Hiroshima Population of Buergeria buergeri (Anura, Rhacophoridae)

Buergeria buergeri is female heterozygous in sex determination; chromosome pair No. 7 in this species is a pair of sex chromosomes of the ZZ/ZW type. Genetic analysis of AAT-1 variants was carried out to elucidate the mode of inheritance of this locus by starch-gel electrophoresis using field-caught females and males and their offspring produced by artificial crossings. The results showed that the AAT-1 locus is sex-linked and that alleles are expressed on the Z chromosome, but not the W chromosome. It is evident that the AAT-1 gene of female offspring is hemizygous and that the allele present is on the Z chromosome, which is derived from the male parent.     

A common Lithuanian mutation causing familial hypercholesterolemia in Ashkenazi Jews.

Familial hypercholesterolemia (FH) is an autosomal dominant disease caused by mutations in the low-density-lipoprotein (LDL) receptor. Here we characterize an LDL-receptor founder mutation that is associated with a distinct LDL-receptor haplotype and is responsible for FH in 35% of 71 Jewish-Ashkenazi FH families in Israel. Sixty four percent (16/25) of the Ashkenazi patients who carry this mutant allele were of Lithuanian origin. The mutation was not found in 47 non-Ashkenazi FH families. This mutation was prevalent (8/10 FH cases) in the Jewish community in South Africa, which originated mainly from Lithuania. The mutation, a 3-bp in-frame deletion that would result in the elimination of Gly197, has been previously designated FH-Piscataway. PCR amplification of a DNA fragment that includes the mutation in heterozygous individuals results in the formation of a heteroduplex that can be demonstrated by PAGE and used for molecular diagnosis.     

Mutation in a sex-determining gene in rainbow trout: detection and genetic analysis

In rainbow trout (Oncorhynchus mykiss), the acknowledged sex-determining system is genetic sex determination (GSD) with female homogamety (female symbolXX-male symbolXY). Subsequently, mitotic gynogens are all expected to be females. Unexpected maleness was fortuitously observed in a mitotic gynogenetic family of rainbow trout (13 males out of 27). An equal ratio of males and females suggested the possible segregation of some Mendelian sex-influencing factor. In order to perform a comprehensive analysis of the inheritance and expression of the factor involved, the transmission of maleness was studied across the next three generations, using both conventional and/or meiotic and mitotic gynogenetic offspring. On the whole, males as well as intersexes were observed in crosses between two expected carrier parents, and in gynogenetic offspring of expected carrier females, but not in crosses between one expected carrier parent and one normal XX control. Sex ratios in the different crosses often fitted Mendelian proportions, but not always. Both excess and lack of maleness were observed. The simplest hypothesis consistent with most results is a one-locus model, assuming the existence of a mutation (termed mal) of a sex-determining gene, which is able to override the primary XX mechanism of sex determination and to induce the development of testicular tissue in the gonads of expected XX individuals. The one-locus model requires that the mal mutation usually, but not systematically, behave as a recessive mutation and have a limited penetrance, that is, heterozygous (mal/+) may be sex reversed, homozygous (mal/mal) may remain female, and carrier individuals may undergo partial masculinization alone (many intersexes were recorded). Inconsistency in sex ratios among offspring of parents expected to respond the same way was recorded, indicating that other modifier loci may also be involved. Finally, the occurrence of both males and females in clonal progenies showed that epigenetic factors also likely influence the expression of maleness. The effects of the mal mutation are compared to similar mutations recently described in other fish species. The nature and location of the mal gene (carried by heterochromosomes or an autosomal pair) is briefly discussed in view of the knowledge recently acquired on the subject.     

Sexual Differences in Parental Investment in Response to Parent‐Absent Calls

Begging in birds is a complex behaviour used by nestlings to solicit feeds from caregivers. Besides calling when parents are present, nestlings of some species also perform less conspicuous repeat calls when parents are absent. The fact that these calls are produced when parents are not at the nest does not mean that parents cannot hear them when they approach the nest or forage in its vicinity. In this study, we experimentally investigated the relationship between parent‐absent repeat calls (ARC) and frequency of parental visits, considering parent/offspring communication as a possible implication of these acoustic signals. A playback experiment was conducted to detect changes in parental investment in response to increases in parent‐ARC, expecting a differential sexual response. Results showed that females clearly responded to repeat calls, increasing their visit rate significantly with respect to females that received the control treatment. Males, on the contrary, did not change their visit rate in response to the treatment. This result provides evidence for a role of parent/offspring communication in parent‐absent repeat calling, an additional function to sibling negotiation processes. The sex‐specific response that we found is in agreement with previous studies that have found that females are more responsive than males to variation in solicitation and hunger signals performed by nestlings.     

Novel compound heterozygous mutations in SLC5A2 are responsible for autosomal recessive renal glucosuria

Familial renal glucosuria is an inherited renal tubular disorder. A homozygous nonsense mutation in the SLC5A2 gene, encoding the sodium/glucose co-transporter SGLT2, has recently been identified in an affected child of consanguineous parents. We now report novel compound heterozygous mutations in the son of non-consanguineous parents. One allele has a p.Q167fsX186 mutation, which is expected to produce a truncated protein, and the other a p.N654S mutation involving a highly conserved residue. These findings confirm that mutations in the SLC5A2 gene are responsible for recessive renal glucosuria.     

Sexual dimorphism,survival, and parental investment in relation to offspring sex in a precocial bird

Differential growth rate between males and females, owing to a sexual size dimorphism, has been proposed as a mechanism driving sex‐biased survival. How parents respond to this selection pressure through sex ratio manipulation and sex‐biased parental investment can have a dramatic influence on fitness. We determined how differential growth rates during early life resulting from sexual size dimorphism affected survival of young and how parents may respond in a precocial bird, the black brant Branta bernicla nigricans. We hypothesized that more rapidly growing male goslings would suffer greater mortality than females during brood rearing and that parents would respond to this by manipulating their primary sex ratio and parental investment. Male brant goslings suffered a 19.5% reduction in survival relative to female goslings and, based on simulation, we determined that a female biased population sex ratio at fledging was never overcome even though previous work demonstrated a slight male‐biased post‐fledging survival rate. Contrary to the Fisherian sex ratio adjustment hypothesis we found that individual adult female brant did not manipulate their primary sex ratio (50.39% male, n = 645), in response to the sex‐biased population level sex ratio. However, female condition at the start of the parental care period was a good predictor of their primary sex ratio. Finally, we examined how females changed their behavior in response to primary sex ratio of their broods. We hypothesized that parents would take male biased broods to areas with increased growth rates. Parents with male biased primary sex ratios took broods to areas with higher growth rates. These factors together suggest that sex‐biased growth rates during early life can dramatically affect population dynamics through sex‐biased survival and recruitment which in turn affects decisions parents make about sex allocation and sex‐biased parental investment in offspring to maximize fitness.     

Transmission ratio distortion in offspring of mouse heterozygous carriers of a (7.18) Robertsonian translocation

Transmission ratio distortion (TRD) is defined as a significant departure from expected Mendelian ratios of inheritance of an allele or chromosome. TRD is observed among specific regions of the mouse and human genome and is frequently associated with chromosome rearrangements such as Robertsonian (Rb) chromosomes. We intercrossed mice heterozygous for a (7.18) Rb translocation and genotyped chromosomes 7 and 18 in 1812 individuals, 47% of which were informative for chromosome segregation. We substantiated previous findings that females were less likely than expected to transmit the Rb chromosome to their offspring. Surprisingly, however, we report that heterozygous males transmitted the Rb translocation chromosome significantly more frequently than the acrocentrics. The transmission of the Rb chromosome was not significantly influenced by either the sex of the Rb grandparent or the strain of the Rb.     

Polymorphism of M factors in populations of the housefly, Musca domestica L., in Turkey

M factors, which determine maleness in Musca domestica, were found on the second, third, fourth and fifth linkage groups in housefly populations of Turkey. As in European populations, the male-determining factor was more frequently located on linkage group III (MIII). Some males homozygous or double heterozygous for M factors were identified. Deviations from a 1:1 sex ratio in favour of males, as well as mosaics for somatic marker mutations and sexual mosaics (gynandromorphs), were also observed. The results reveal an extensive polymorphism in the sex-determining system.     

No patrigenes required for femaleness in the haplodiploid wasp Nasonia vitripennis

The parasitoid wasp Nasonia vitripennis is an emerging model organism for developmental and behavioral genetics. It reproduces by haplodiploidy; males typically develop parthenogenetically from haploid eggs and females from fertilized diploid eggs. A polyploid mutant strain is available in which females are triploid and lay haploid and diploid eggs that normally develop into males when unfertilized. In contrast to previous reports, approximately 2% of triploid females were found to occasionally produce daughters as well as gynandromorphs from diploid unfertilized eggs. Daughter production increased with age and differed among familial lineages. This is the first report of parthenogenetic female development in Nasonia. The results show that a paternally provided genome is not required for femaleness and call for modifications of existing models of sex determination in Nasonia.