Male Recombination Frequencies Research Articles

Drosophila ananassae: a species characterized by spontaneous male recombination in appreciable frequency

Mutation and recombination are primarily responsible for generating the genetic variability in natural populations of microorganisms, plant and animal species including humans. Upon such genetic variations, elemental forces of evolution such as natural selection, random genetic drift and migration operate to bring about micro-evolutionary changes. Recombination or crossing-over produces new combinations of genes due to interchange of corresponding segments between nonsister chromatids of homologous chromosomes, thus, it is an important evolutionary factor. Since the time of T. H. Morgan, Drosophila has been subjected to extensive investigations on crossing over while employing a number of markers, which were used for gene mapping. Interestingly, recombination occurs in females of D. melanogaster but not in males. Later on, male crossing over was investigated in various species and its occurrence was reported in D. melanogaster, D. ananassae, D. simulans, D. willistoni, D. littoralis and D. bipectinata. Recombination occurs at very low rate in all these species except for D. ananassae, which shows spontaneous male crossing over in appreciable frequency, which is meiotic in origin. This unusual phenomenon in D. ananassae is influenced by various genetic factors as well as it shows strain variation as far as frequency of male recombination is concerned. Further, the presence of chiasmata during meiosis in males at a frequency capable of accounting for the observed recombination frequency extends evidence for meiotic origin of recombination in males of D. ananassae.

Dynamics of male meiotic recombination frequency during plant development using Fluorescent Tagged Lines in Arabidopsis thaliana

Meiotic homologous recombination plays a central role in creating genetic variability, making it an essential biological process relevant to evolution and crop breeding. In this study, we used pollen-specific fluorescent tagged lines (FTLs) to measure male meiotic recombination frequency during the development of Arabidopsis thaliana. Interestingly, a subset of pollen grains consistently shows loss of fluorescence expression in tested lines. Using nine independent FTL intervals, the spatio-temporal dynamics of male recombination frequency was assessed during plant development, considering both shoot type and plant age as independent parameters. In most genomic intervals assayed, male meiotic recombination frequency is highly consistent during plant development, showing no significant change between different shoot types and during plant aging. However, in some genomic regions, such as I1a and I5a, a small but significant effect of either developmental position or plant age were observed, indicating that the meiotic CO frequency in those intervals varies during plant development. Furthermore, from an overall view of all nine genomic intervals assayed, both primary and tertiary shoots show a similar dynamics of increasing recombination frequency during development, while secondary and lateral shoots remain highly stable. Our results provide new insights in the dynamics of male meiotic recombination frequency during plant development.

The effect of temperature on the male and female recombination landscape of barley.

Barley (Hordeum vulgare) is a crop of global significance. However, a third of the genes of barley are largely inaccessible to conventional breeding programmes as crossovers are localised to the ends of the chromosomes. This work examines whether crossovers can be shifted to more proximal regions simply by elevating growth temperature. We utilised a genome-wide marker set for linkage analysis combined with cytological mapping of crossover events to examine the recombination landscape of plants grown at different temperatures. We found that barley shows heterochiasmy, that is, differences between female and male recombination frequencies. In addition, we found that elevated temperature significantly changes patterns of recombination in male meiosis only, with a repositioning of Class I crossovers determined by cytological mapping of HvMLH3 foci. We show that the length of synaptonemal complexes in male meiocytes increases in response to temperature. The results demonstrate that the distribution of crossover events are malleable and can be shifted to proximal regions by altering the growth temperature. The shift in recombination is the result of altering the distribution of Class I crossovers, but the higher recombination at elevated temperatures is potentially not the result of an increase in Class I events.

Linkage analysis and map construction in genetic populations of clonal F1 and double cross.

In this study, we considered four categories of molecular markers based on the number of distinguishable alleles at the marker locus and the number of distinguishable genotypes in clonal F1 progenies. For two marker loci, there are nine scenarios that allow the estimation of female, male, and/or combined recombination frequencies. In a double cross population derived from four inbred lines, five categories of markers are classified and another five scenarios are present for recombination frequency estimation. Theoretical frequencies of identifiable genotypes were given for each scenario, from which the maximum likelihood estimates of one or more of the three recombination frequencies could be estimated. If there was no analytic solution, then Newton-Raphson method was used to acquire a numerical solution. We then proposed to use an algorithm in Traveling Salesman Problem to determine the marker order. Finally, we proposed a procedure to build the two haploids of the female parent and the two haploids of the male parent in clonal F1. Once the four haploids were built, clonal F1 hybrids could be exactly regarded as a double cross population. Efficiency of the proposed methods was demonstrated in simulated clonal F1 populations and one actual maize double cross. Extensive comparisons with software JoinMap4.1, OneMap, and R/qtl show that the methodology proposed in this article can build more accurate linkage maps in less time.

Three Cycles of Recurrent Selection for Altered Recombination Frequency in Maize

The variability among progeny in a plant breeding population depends on the amount of recombination that occurs in meiosis preceding selection. The recombination arises either from the independent assortment of chromosomes or from crossing over during chromosome synapsis. Crossing over is not a constant value; it differs based on background genotype. This research determined the effectiveness of three cycles of recurrent selection for increased or decreased crossing over in Zea mays L. Testcrosses measured male recombination frequency on three chromosomes: 4, su1‐c2; 5, a2‐bt1‐pr1; and 9, sh1‐bz1‐wx1 Sixty plants from each of three populations (cycle 0 [C0], cycle 3 high recombination [C3HR], and cycle 3 low recombination [C3LR]) were evaluated. The mean recombination frequency changes between C0 and C3HR are significant at all chromosome regions (su1‐c2, +5%; a2‐pr1, +24%; sh1‐wx1, +8%). The mean recombination frequency changes between C0 and C3LR are significant at the chromosome 4 (su1‐c2,‐15%) and 5 (a2‐pr1,‐27%) linkage groups. The mean recombination frequency did not change significantly from C0 to C3LR at either of the chromosome 9 regions. Compared to the C0 population, the sum of the genetic distances at these chromosome regions increased 9.5% in the C3HR population and decreased 14.9% in the C3LR population. Selection for high or low recombination frequency successfully modified recombination frequency.

Pseudoautosomal Linkage of Hodgkin Disease

Heritable factors appear to account for much of the risk for Hodgkin disease (HD). There is evidence for an HLA-linked gene, but other predisposing loci remain unaccounted for. The observation of a family coinheriting both HD and Leri-Weill dyschondrosteosis (LWD) suggests that a gene conferring risk for HD resides adjacent to the LWD locus. The gene responsible for LWD, SHOX, localizes to the short-arm pseudoautosomal region (PAR) of the X and Y chromosomes. A unique segregation pattern for PAR-linked genes has been predicted-that affected sibs will tend to be same sex. An excess of sex-concordant affected sib pairs with HD has been noted but has been attributed to an environmental etiology. These two observations-sex concordance in sib pairs with HD and cosegregation of HD and LWD-impelled a test of the hypothesis that there is a PAR-localized gene for HD. By first scoring recombinations dissociating sex from phenotype in individuals from pedigrees with LWD, we determined a male maximum recombination frequency (thetamax) of.405. This places SHOX near the short-arm telomeres of the sex chromosome and supports the prediction that PAR recombination is obligatory for spermatogenesis. By inferring recombinations between HD and sexual phenotype in sib pairs, we predict, for the postulated HD gene, a male thetamax as high as .254, which places it in proximity to SHOX. Morton's nonparametric affected-sib-pair "beta" model was used in the evaluation of linkage between HD and phenotypic sex and gave a LOD score of 2.41. Using this approach, we reevaluated evidence for HLA linkage in HD in haplotyped sib pairs and found a LOD score of 2.00. The resulting beta values indicate that the putative PAR- and HLA-linked loci account for 29% and 40%, respectively, of the heritability of HD in an American population.

Repeatability and heritability of divergent recombination frequencies in the Iowa Stiff Stalk Synthetic (Zea mays L.)

Variability in recombination frequency was reported in the Iowa Stiff Stalk Synthetic. The objectives of the present research were to verify the differences in recombination frequency among individuals in the Iowa Stiff Stalk Synthetic maize population and to determine if the recombination frequency differences persisted among the S1 progeny. Testcrosses to measure male recombination frequency on three chromosomes (4, su1-c2; 5, a2-bt1-pr1; 9, sh1-bz1-wx1) were repeated for eight S0 individuals. Recombination frequencies were repeatably divergent among those individuals which were selected based on high or low recombination frequencies on specific chromosomes. Individuals which had been selected for long and short total map distances across the three chromosome regions produced repeatably divergent recombination frequencies only at the su1-c2 region. The recombination frequencies of the S1 lines, derived from the S0 individuals which had the most divergent recombination frequencies on a single chromosome, were significantly different. The broadsense heritability estimates derived from the regression of six S1 lines on six S0 individuals ranged from 0.69 to 0.20 for the five chromosome regions. We conclude that genetic differences for recombination frequency exist in this population and that modification by selection should be possible.

Genetic and cytological mapping of a "Y-2" translocation in the Mediterranean fruit fly Ceratitis capitata.

In this paper we analyze genetically and cytologically a Y-chromosome 2 translocation with several markers, some of which are potentially useful for large scale sex separation. The breakpoint of this Y-2 translocation is located at region 6B on the trichogene polytene chromosome map. It is found that, in strains carrying this TY-2, only 40% of the fertilized eggs survived to the adult stage, 26% of them dying as embryos, 27% as larvae, and 7% as pupae. Early lethality is explained by the nonviability of adjacent-1 products of meiosis containing a deletion of section 1A-6B. The reciprocal segregation products, carrying this chromosome segment in triplicate, survive until late stages. By analyzing the phenotype of the individuals we conclude that all markers used in this study are located outside the triplicated region and that the male determining factor is not included in the piece of the Y chromosome translocated to chromosome 2. The male recombination frequencies of several genes located on chromosome 2 relative to the breakpoint of translocation T5038 have also been studied here.

A comparison of male and female recombination frequency in wheat using RFLP maps of homoeologous group 6 and 7 chromosomes

A novel approach was used to compare male and female recombination rates in wheat. Doubled haploid lines were developed from an F1 using two distinct approaches: the anther-culture technique and the Hordeum bulbosum system, from which sets of lines were developed from "male" and "female" meioses, respectively. The genotype of the lines was established at RFLP and isozyme markers polymorphic on chromosomes of homoeologous groups 6 and 7, and "male" and "female" linkage maps were calculated using this information. The markers in one segment of chromosome 6B exhibited disturbed segregation frequencies in the anther-culture population. The "male" and "female" maps differed significantly in recombination frequency between some markers on two chromosomes, and these were consistent in direction within chromosomes and inconsistent in direction between chromosomes. In two of the four chromosomes studied the "male" map was much longer than the "female" map. These results suggest that significant differences may exist in male and female recombination frequencies in bread wheat which are specific to certain chromosomal segments but are inconsistent in direction between chromosomes. Other factors, such as environmental influences, may also be important in creating differences.

RFLP mapping inBrassica nigraindicates differing recombination rates in male and female meioses

A genetic linkage map of Brassica nigra, comprised of 288 loci in eight linkage groups, was constructed. The linkage groups varied in size from 72 to 159 cM and the total map length was 855 cM. The recurrent parent used in the backcross was extremely heterozygous. This allowed recombination to be estimated separately for female (recurrent parent) meiosis and male (F1) meiosis over a large proportion of the genome. Significant differences between male and female recombination frequencies were observed on all six linkage groups where data was available for both sexes. Enhanced male recombination frequencies were observed that were associated with proterminal regions, while enhanced female recombination frequencies were adjacent to putative centromeres. It is possible that the distinct genotypes of the F1 (male) and recurrent (female) parents contributed to the observed differences in recombination. However, this study emphasizes the need to consider potential sex differences, in both the rate and the position of recombination, when planning genetic experiments and breeding programmes.

Variability of recombination frequencies in the Iowa Stiff Stalk Synthetic (Zea mays L.)

Variability in recombination frequency has been reported in several plant populations. The objectives of the present research were to establish the range in variability in recombination among genotypes in the important corn population Iowa Stiff Stalk Synthetic and to identify individual genotypes which produced increased or decreased recombination frequencies. Approximately 150 individual S0 plants were testcrossed to measure male recombination frequency on three chromosomes: 4, sul-c2; 5, a2-btl-pr1; and 9, sh1-bz1-wx1. Although the variance component for individuals accounted for only 20-33% of the total variation, highly significant variability among individuals was present at all chromosome regions. Thus the environmental effects did not prevent measurement of differences between S0 individuals. At each chromosome region, individual genotypes with recombination frequencies at least two standard deviations above or below the population mean were isolated. Reports in the literature suggest that the variability reported here for the BSSS population should be representative of that present in other corn breeding populations. Recombination frequencies were positively correlated between adjacent regions of chromosome 9 and also between adjacent regions of chromosome 5. Recombination frequencies were positively correlated between both regions on chromosome 5 with the su1-c2 region of chromosome 4. Negative correlations were observed between chromosome 9 recombination and recombination in each region of chromosomes 4 and 5. Thus rankings of S0 individual recombination frequencies were not consistent for all three chromosomes.

A Continuous Linkage Map of 22 Short Tandem Repeat Polymorphisms on Human Chromosome 12

A continuous linkage map consisting of 22 short tandem repeat polymorphisms has been constructed for human chromosome 12 using 23 non-CEPH pedigrees. The markers were distributed at an average distance of 9.35 cM (3.1-33.9 cM). Eighteen of the markers could be positioned uniquely with a likelihood of > 1000:1. The physical locations of some of the markers suggest that the map covers 85-95% of the chromosome. This framework map of 18 markers has a female length of 213 cM and a male length of 131 cM. Female recombination frequencies were greater than male recombination frequencies except in the distal portion of the short arm. The map provides confirmatory evidence for orders established previously on CEPH pedigrees and uniquely positions 4 additional markers (CD4, ATPSB, D12S56, PLA2).

Chromosome interactions in P-M dysgenic male recombination of Drosophila melanogaster.

The frequency, distribution and structure of P elements on the second and third chromosomes of Texas 1, a wild-type inbred strain of Drosophila melanogaster, were investigated by in situ hybridization. These autosomes were isolated individually and used as P-element donors to study the frequency and distribution of male recombination events generated on recipient chromosomes which were originally devoid of P sequences. The P-element array of chromosome 2 was shown to generate higher male recombination frequencies on chromosome 3 than vice versa, despite having fewer P factors and fewer P elements in general. This is likely to be due to the presence and distribution of specific P-deletion derivatives, which vary in their ability to repress P mobility. The male recombination generated on recipient chromosomes is associated with the insertion of donated P sequences, but only in a small minority of cases could a novel P-element site be detected at, or near, the recombination breakpoint. The majority of such breakpoints appear to be associated either with unsuccessful P insertion, or with the action of P transposase attracted by P elements newly inserted elsewhere on the recipient chromosome. Recent evidence also suggests that a small proportion of the breakpoints may be associated with the action of P transposase alone. Male recombination breakpoints appear to be distributed effectively at random along the recipient autosomes, and their frequency of occurrence was shown to correlate with the physical length of DNA available between markers, as revealed by the polytene map distance.

Continuous linkage map of human chromosome 14 short tandem repeat polymorphisms

Nine moderately to highly informative short tandem repeat polymorphisms were assigned to chromosome 14 using somatic cell hybrids and were mapped using linkage analysis. The nine markers formed a continuous linkage map covering almost the entire long arm from 14q11.2 to q32. The markers filled a large gap within previously reported linkage maps for this chromosome. Best order of the new loci from q11.2 to q32 was D14S50, D14S54, D14S49, D14S47, D14S52, D14S53, D14S55, D14S48, and D14S51. The order shown for all adjacent pairs of loci was very strongly favored with the exception of loci pair D14S55 and D14S48, for which the order was moderately favored. Map lengths for the nine loci were 142 cM in females and 72 cM in males. Female recombination frequencies exceeded male recombination frequencies in the middle and distal portions of the map.

Male crossing over and genetic sexing systems in the Australian sheep blowfly Lucilia cuprina

Field-female killing (FK) systems based on deleterious mutations and Y-autosome translocations are being evaluated for genetic control of the Australian sheep blowfly, Lucilia cuprina. Experience during field trials has shown that mass-reared colonies of FK strains are subject to genetic deterioration, caused mainly by genetic recombination in males. A previous study found higher male recombination frequencies in two Y-linked translocation strains than in chromosomally normal males. However, the results of the present study indicate that breakage of the Y chromosome is neither sufficient nor necessary for increased levels of male recombination. The frequency of male recombination appears to be unrelated to the presence of specific chromosome rearrangements.

Molecular cloning and analysis of forked locus in Drosophila ananassae

Drosophila ananassae, in spite of its unique genetic characters including high mutability and high frequency of male recombination has been little studied at the molecular level. Since the species is very similar to D. melanogaster, it is natural to expect that the high spontaneous mutation rate and male recombination may be caused by inserted mobile DNA elements, as in D. melanogaster. The present study was designed to determine whether or not most spontaneous mutations of the forked locus of D. ananassae are caused by insertion sequences as is found in D. melanogaster. I cloned the forked locus of D. ananassae, using forked DNA from D. melanogaster as a probe and investigated the molecular structure and transcription of the gene by Southern and Northern analyses. The results suggest that the restriction map and transcriptional patterns of the forked locus of D. ananassae are similar to those of D. melanogaster, while the spontaneous mutations available in D. ananassae are induced quite differently from those that have been described in D. melanogaster; in four (f;cd, f10-14, f49 and f86) out of eight forked alleles, neither insertions nor deletions were detected around the forked coding region. Forked transcripts are expressed in a pattern which is very similar to that of D. melanogaster and were all of normal size in these mutants. The other four mutants (f10-3, f9-10, f83i and f79b) had insertion sequences upstream of the forked coding region, while transcripts of the forked gene were of normal size. Hence, none of the eight mutations studied appear to affect the structure of the forked transcripts.

A refined linkage map for DNA markers around the pericentromeric region of chromosome 10

A refined genetic linkage map for the pericentromeric region of human chromosome 10 has been constructed from data on 12 distinct polymorphic DNA loci as well as the locus for multiple endocrine neoplasia type 2A (MEN 2A), a dominantly inherited cancer syndrome. The map extends from D10S24 (at 10p13–p12.2) to D10S3 (at10q21–q23) and is about 70 cM long. Overall, higher female than male recombination frequencies were observed for this region, with the most remarkable female excess in the immediate vicinity of the centromere, as previously reported. Most of the DNA markers in this map are highly informative for linkage and the majority of the interlocus intervals are no more than 6 cM apart. Thus this map should provide a fine framework for future efforts in more detailed mapping studies around the centromeric area. A set of ordered crossovers identified in this work is a valuable resource for rapidly and accurately localizing new DNA clones isolated from the pericentromeric region.

Sex-related differences in crossing over in Caenorhabditis elegans.

In the nematode Caenorhabditis elegans, hermaphrodite recombination has been characterized and is the basis of the genetic map used in this organism. In this study we have examined male recombination on linkage group I and have found it to be approximately one-third less than that observed in the hermaphrodite. This decrease was interval-dependent and nonuniform. We observed less recombination in the male in 5 out of 6 intervals examined, and no observable difference in one interval on the right end of LG I. Hermaphrodite recombination frequencies are the result of recombination in two germlines; oocyte and hermaphrodite spermatocytes. We have measured recombination in the oocyte and have found it to be approximately twofold lower than that calculated for hermaphrodite spermatocytes and not significantly different from the male spermatocyte frequency. Thus, recombination frequencies appear to be a function of gonad physiology rather than the sex of the germline. Evidence from experiments examining the effect of karyotype on recombination in males sexually transformed by the her-1 mutation into XO hermaphrodites (normally XX), suggests the sexual phenotype rather than genotype determines the recombination frequency characteristic of a particular sex. Hermaphrodite recombination is known to be affected by temperature, maternal age, and the rec-1 mutation. We have examined the effect of these parameters on recombination in the male and have found male recombination frequency increased with elevated temperatures and in the presence of Rec-1, and decreased with paternal age.

Male Recombination in a Genetic Sexing Strain of Ceratitis capitata (Diptera: Tephritidae) and Its Effect on Stability

Male recombination was studied between the Y-translocated loci or (orange eye) and wp (white pupae) in a genetic sexing strain of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann). This strain normally produces wild type males, whereas females are homozygous for the or and wp alleles. In previous mass rearing, another strain with the same translocation was highly unstable. In this study, an overall male recombination frequency of 0.07 and 0.24% was observed between the or gene and the translocation breakpoint (T) and between wp and T, respectively. Only one of the two alleles appeared to be physically linked to the Y chromosome. All aberrant male phenotypes still contained the translocation, indicating that no reversal to the normal karyotype had taken place. A strong positive interference on recombination was observed; a recombinant event between T and wp led in one-third of the cases to a recombinant event also occurring between T and or . Male recombination appeared to be responsible for the initiation of the breakdown of the mass-reared genetic sexing strain, but it could not by itself account for the subsequent rate of breakdown of this strain. The possible role of other factors in accelerating the rate of this breakdown is discussed.

Cytoplasmic suppressor effect on male crossing over in Drosophila ananassae.

A reciprocal cross difference in the frequency of male recombination was detected in progeny of hybrids between e se; bri ru and Tonga stocks of Drosophila ananassae. A chromosomal enhancer-cytoplasmic suppressor system determining male crossing over in D. ananassae was identified that appeared to be similar to, but distinct from, that described previously by Hinton (1974). The higher the temperature at which males were reared, the less reciprocal cross ratio in the frequency of male recombination was found. The reciprocal cross differences might be explained by a cytoplasmic suppressor of the Tonga stock and a nuclear chromosomal gene(s). This chromosomal gene is dominant for the reducing the frequency of male recombination, and is located on the 2nd chromosome of the Tonga stock. The maternally transmitted cytoplasmic suppressor was maintained by other chromosomal regions (genes) on both 2nd and 3rd chromosomes of the Tonga stock.