Scholarly Literature

This is a database of scholarly literature that concentrates currently on natural and engineered selfish genetic elements (gene drives).  The latest are shown here.
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Evidence for B chromosome drive suppression in the grasshopper Eyprepocnemis plorans

4393
Herrera, JAL, M. D.; Cabrero, J.; Shaw, M. W.; Camacho, J. P. M.,  Heredity,  76:633-639. 1996-01-11 00:00:00.
The grasshopper Eyprepocnemis plorans is polymorphic for both a B chromosome and a heterochromatic segment of chromatin on the smallest autosome. Females transmit these to their offspring more frequently after copulating with a male from a population without Bs than after copulating with a male from their own population. Paternity analyses using the heterochromatic segment as a marker showed that the effect of male on female transmission does not depend on fertilization because it occurs even when all the eggs are fertilized by sperm from another mating. The possible mechanisms include behavioural differences in mating and transfer of substances affecting female meiosis in male ejaculate. The data support the idea that the B chromosome is initially subject to meiotic drive in populations in which it has not previously existed, and that genes which suppress this drive are then selected.

Segregation distortion of the CTG repeats at the myotonic dystrophy locus

4392
Chakraborty, RS, D. N.; Deka, R.; Yu, L. M.; Shriver, M. D.; Ferrell, R. E.,  American Journal of Human Genetics,  59:109-118. 1996-01-10 00:00:00.
Myotonic dystrophy (DM), an autosomal dominant neuromuscular disease, is caused by a CTG-repeat expansion, with affected individuals having greater than or equal to 50 repeats of this trinucleotide, at the DMPK locus of human chromosome 19q13.3. Severely affected individuals die early in life; the milder form of this disease reduces reproductive ability. Alleles in the normal range of CTG repeats are not as unstable as the (CTG)(greater than or equal to 50) alleles. In the DM families, anticipation and parental bias of allelic expansions have been noted. However, data on mechanism of maintenance of DM in populations are conflicting. We present a maximum-likelihood model for examining segregation distortion of CTG-repeat alleles in normal families. Analyzing 726 meiotic events in 95 nuclear families from the CEPH panel pedigrees, we find evidence of preferential transmission of larger alleles (of size less than or equal to 29 repeats) from females (the probability of transmission of larger alleles is .565 +/- 0.03, different from .5 at P approximate to .028). There is no evidence of segregation distortion during male meiosis. We propose a hypothesis that preferential transmission of larger CTG-repeat alleles during female meiosis can compensate for mutational contraction of repeats within the normal allelic size range, and reduced viability and fertility of affected individuals. Thus, the pool of premutant alleles at the DM locus can be maintained in populations, which can subsequently mutate to the full mutation status to give rise to DM.

The inheritance of B chromosomes in Allium schoenoprasum L

4391
Bougourd, SMP, A. B.,  Chromosome Research,  4:151-158. 1996-01-09 00:00:00.
The inheritance of B chromosomes has been investigated in Allium schoenoprasum from the River Wye, Powys; controlled crosses between plants of known B chromosome constitution were carried out, and the numbers of Bs present in the progenies scored. There was considerable heterogeneity in B chromosome transmission rates across the range of B chromosome numbers, through both the male and female lines, and in crosses involving odd and even numbers of Bs. The mean B number of the progeny was lower than the Mendelian expectation in 41 of the 57 crosses, significantly so in about a third of cases. No progeny had a mean B number significantly higher than expected. The mean transmission rate per B was not significantly different between parents with different numbers of Bs, in either the male or female line, or between plants carrying odd or even numbers of Bs. Transmission through the male line (0.43) was higher than through the female line (0.35), but not significantly so. The overall mean transmission rate per B (0.4), estimated from all crosses, was significantly lower than the expected rate of 0.5. This study provides conclusive evidence that B chromosomes in A. schoenoprasum from the River Wye lack an effective accumulation mechanism and, furthermore, show significant losses during transmission to the progeny of controlled crosses.

Low frequency of mouse t haplotypes in wild populations is not explained by modifiers of meiotic drive

4390
Ardlie, KGS, L. M.,  Genetics,  144:1787-1797. 1996-01-08 00:00:00.
t haplotypes are naturally occurring forms of mouse chromosome 17 that show non-Mendelian transmission from heterozygous +/t males. In laboratory studies, transmission ratios of greater than or equal to 0.90 or higher are typically observed. With transmission ratios of this level, theoretical analyses predict high frequencies of t haplotypes (similar to 75%) in wild populations. In contrast, empirical frequencies of only 15-25% are typically found. This has led to the suggestion that modifiers of drive may play a role in reducing t frequencies. We have measured transmission ratio distortion (TRD) levels in wild +/t mice to examine this hypothesis. TRD was very high in both litters collected from wild-caught pregnant females, and in wild litters bred in the laboratory (mean = 0.9). Contrary to the results of other studies, we found no difference in TRD levels between semilethal and lethal t haplotypes nor between litters conceived from cycling or postpartum estrus. We found three litters with aberrantly low TRDs that were all multiply sired, although the role this might play in natural populations is unknown. These findings show a general absence of modifiers of drive in natural populations and suggest that other factors are responsible for the low observed frequencies of wild t haplotypes.

Gene transfer into the Medfly, Ceratitis capitata, using a Drosophila hydei transposable element.

6269
T. G. Loukeris, I. Livadaras, B. Arca, S. Zabalou and C. Savakis,  Science,  270:2002-2005. 1995-12-22 16:35:47.
Exogenous functional DNA was introduced into the germline chromosomes of the Mediterranean fruit fly (medfly) Ceratitis capitata with a germline transformation system based on the transposable element Minos from Drosophila hydei. Transformants were identified as phenotypic revertants of a white-eyed mutation carried by the recipient strain. Clusters of transformants were detected among the progeny of 390 individuals screened for germline transformation. Five independent and phenotypically active integration events were identified, in each of which a single copy of the transposon was inserted into a different site of the medfly genome. Molecular analysis indicates that they represent transposase-mediated insertions of the transposon into medfly chromosomes.

Meiotic drive in female mice: An essay

4407
Ruvinsky, A,  Mammalian Genome,  6:315-320. 1995-01-05 00:00:00.
Since the rediscovery of Mendel's laws, geneticists have accumulated various examples in which equal meiotic segregation in heterozygotes is violated. However, only a few natural meiotic drive systems have been characterized in detail and the majority of these are sex chromosome linked (Hurst and Pomiankovski 1991a). In animals, only two autosomal meiotic drive systems have been thoroughly investigated: the t complex in Mus musculus (Lyon 1991; Silver 1993) and the Segregation Distorter system (SD) in Drosophila melanogaster (Lyttle 1991). Both affect heterozygous males. Recently Agulnik and associates (1990a, 1993c, 1993d) have found and described a new meiotic drive system that disturbs normal segregation in heterozygous female mice. The system is the main target of this review, which also includes a comparative analysis of other drive systems to establish a likely scenario of their origin, evolution, and stability in natural populations.

Sex-ratio distortion in Drosophila simulans – cooccurrence of a meiotic drive and a suppressor of drive

4406
Mercot, HA, A.; Jacques, M.; Montchampmoreau, C.,  Journal of Evolutionary Biology,  8:283-300. 1995-01-04 00:00:00.
A sex-ratio distortion factor was found at high frequency in D. simulans strains from Seychelles and New Caledonia. This factor is poorly or not expressed within those strains which are resistant to it. Its presence was detected by crossing females from New Caledonia or the Seychelles with males from a different geographic origin. Most of the Fl males obtained produced an excess of females (up to 99%) in their progeny. The two strains are infected with Wolbachia, but these micro-organismms are not involved in the sex-ratio distortion. The sex-ratio factor is shown to be an X-linked meiotic driver; nuclear resistance factor(s) act by suppressing the drive. It is likely that the same X-located driver invaded the two populations, which subsequently developed resistance factor(s) against it.

Tctex2 – a sperm tail surface protein mapping to the t-complex

4405
Huw, LYG, A. S.; Willison, K.; Artzt, K.,  Developmental Biology,  170:183-194. 1995-01-03 00:00:00.
Transmission ratio distortion (TRD) in mouse t-haplotypes remains the most significant example of meiotic drive in vertebrates. While the underlying mechanism that fuels it is still mysterious, TRD is clearly a complex multigene phenomenon. The characterization of Tctex2 (t-complex testis expressed 2) shows it to be one of several candidates for involvement in TRD, Tctex2 maps to the t-complex and encodes a membrane-associated protein found exclusively on the sperm tail. The t-haplotype form of Tctex2 is aberrant in both the level of its expression and its primary amino acid sequence, but is nonetheless translated and transported to its normal location. The multiple amino acid changes in the t-form make it extremely unlikely that it can function normally and, since it is found on sperm tails, suggest that it may actively interfere with the development of normal gamete function in males. The possible role of Tctex2 in t-complex transmission ratio distortion and sterility is discussed. (C) 1995 Academic Press, Inc.

Meiotic drive an Myotonic Dystrophy – Reply

4404
Carey, NJ, K.; Nokelainen, P.; Peltonen, L.; Savontaus, M. L.; Juvonen, V.; Anvret, M.; Grandell, U.; Chotai, K.; Robertson, E.; Middletonprice, H.; Malcolm, S.,  Nature Genetics,  10:133-133. 1995-01-02 00:00:00.
Myotonic dystrophy (DM) is a trinucleotide disorder and in sub-clinical individuals there is considerable variation in the length of the CTG repeat. Two groups have recently analysed the patterns of segregation of different sized alleles at this locus and both report an excess of the longer version of the allele in the progeny of sub-clinical individuals1•2• This excess they claim to be due to meiotic drive1•2• Our re-analysis of these two studies indic

Ascoycete spore killers: Chromosomal elements that distort genetic ratios among the products of meiosis

4417
Raju, NB,  Mycologia,  86:461-473. 1994-01-15 00:00:00.
Spore killers (Sk), studied most extensively in Neurospora, are also known in Podospora, Gibberella and Cochliobolus. Spore killers are no doubt present in natural populations of other fungi. Criteria are outlined here for recognizing their presence and distinguishing them from other causes of ascospore death. Killing occurs when one parent carries the killer element (Sk(K)) and the other carries the sensitive counterpart (Sk(S)). When heterozygous, every ascus contains four normal-sized, viable ascospores and four ascospores that are tiny, undeveloped, and inviable. Spore killers are expressed postmeiotically causing the death of ascospores that do not receive the killer element and resulting in gross distortion of allele ratios for Sk-linked genes. There is little or no ascospore death in homozygous killer x killer or sensitive x sensitive crosses. Sk(K) is centromere-linked in linkage group III of Neurospora crassa and N. intermedia. When Sk is heterozygous, crossing over is blocked in a 30 map unit region that spans the centromere. A sensitive nucleus that would otherwise die is rescued, unchanged, if a killer nucleus is also included in the same ascospore. This has been shown for a developmental giant-ascospore mutant of N, crassa and for the naturally heterokaryotic ascospores of N. tetrasperma and Podospora anserina. As with other segregation-distorters in animals and plants, fungal Spore killers have been found only among strains from nature. Spore killers are fairly common in N. sitophila and Gibberella fujikuroi, but none have been found among natural isolates of N. crassa. In N. intermedia, most strains are sensitive to killing and killers are extremely rare. Some neutral strains are found in nature. These neither kill nor are killed. Resistance to killing is conferred by loci linked to the Sk region. The significance of fungal Spore killers for the individual organism and for populations is discussed.

Characterization of 2 Segregation Distorter revertants: Evidence that the tandem duplication is necessary for SD activity in Drosophila melanogaster

4416
Palopoli, MFD, P.; Wu, C. I.,  Genetics,  136:209-215. 1994-01-14 00:00:00.
Segregation Distorter (SD) is a naturally occurring system of meiotic drive in Drosophila melanogaster. Males heterozygous for an SD second chromosome and a normal homolog (SD+) transmit predominantly SD-bearing sperm. To accomplish this, the Segregation distorter (Sd) locus induces the dysfunction of those spermatids that receive the SD+ chromosome. Recently, P. A. Powers and B. Ganetzky isolated overlapping DNA clones spanning the region of DNA known to contain the Sd gene and identified a 5-kb tandem duplication that is present on all SD chromosomes examined, but is apparently absent from wild-type chromosomes. Here we report a molecular analysis of two spontaneous revertants from an Australian SD chromosome (SD-Arm28). Both of these revertants have lost the 5-kb tandem duplication along with the ability to distort transmission; the critical observation, however, is that they retain the DNA haplotype in the flanking regions (both proximally and distally) that is characteristic of the original SD-Arm28. We propose unequal sister chromatid exchange between the tandem repeats as the only plausible explanation for loss of a repeat while retaining flanking markers. This provides direct evidence that the tandem duplication is indeed necessary for the Sd phenotype. Further, we examined testes-specific levels of both RNA and protein for the nearby Topoisomerase 2 gene. Neither revealed a consistent difference between SD and SD+ strains. We also measured testes-specific levels of RNA using the tandem duplication itself as probe. Our results suggest that there is strong up-regulation of one or several 2.0-2.3-kb transcripts from the duplicated region in the testes of an SD strain. Whether it is this overexpression of transcripts that causes segregation distortion remains to be investigated.

Functional identification of the Segregation Distorter locus of Drosophila melanogaster by germline transformation

4415
McLean, JRM, C. J.; Powers, P. A.; Ganetzky, B.,  Genetics,  137:201-209. 1994-01-13 00:00:00.
Segregation Distorter (SD) is a meiotic drive system in D. melanogaster that results in the failure of SD/SD+ males to transmit SD+ homologs owing to the induced dysfunction of spermatids carrying the normal chromosome. Segregation distorter (Sd), the gene primarily responsible for this distorted transmission, is associated with a novel 12-kb restriction fragment containing a tandem duplication of a 5-kb wild-type segment of genomic DNA. When introduced into appropriate genetic backgrounds by germline transformation, this 12-kb fragment causes full levels of distortion and directs the expression of an Sd-specific 4-kb transcript. Transformants that have lost part of this segment are unable to cause distortion and do not express the 4-kb transcript. These results identify the tandem duplication as Sd.

Selfish DNA as method of pest control

4414
Hastings, IM,  Philosophical Transactions of the Royal Society B-Biological Sciences,  344:313-324. 1994-01-12 00:00:00.
The inheritance of most genes is tightly controlled, governed by the rules of mendelian inheritance if nuclear or uniparental inheritance if cytoplasmic. A few notable genes and cytoplasmic genomes have escaped this regulation. Such genes may spread by increasing their own rate of transmission despite reducing host fitness and may be regarded as 'selfish'. Their population genetics are described and it appears they may impose a significant genetic load on the host population. Modern molecular techniques may enable similar loads to be imposed on pest species either by transferring selfish genes between species, or by linking deleterious genes to a selfish locus. Alternatively, 'modifier' genes that eliminate the virulent, or disease vectorial capacity, of the pest population may be introduced by linkage to a selfish locus. Selfish elements present in multiple copies may be preferable to single-copy elements as the former are capable of a larger reduction in host fitness. The practical application of these agents depends on five factors: (i) the rate of 'reversion' to a non-selfish form; (ii) the evolution of host repressor systems; (iii) their effect on host fitness, which determines their rate of invasion; (iv) the mechanism regulating host population size in the field; and (v) their ease of manipulation in the laboratory. The first two factors are the most uncertain in most systems, but should be amenable to experimental analysis. It is proposed that the development of such techniques may result in powerful new methods of population control which may be applied to both agricultural pests and disease vectors.

Meiotic drive at the myotonic dystrophy locus

4413
Gennarelli, MD, B.; Baiget, M.; Martorell, L.; Novelli, G.,  Journal of Medical Genetics,  31:980-980. 1994-01-11 00:00:00.
The mutation underlying myotonic dystrophy (DM, MIM* 160900) is the expansion of a CTG trinucleotide repeat sequence at the 3' untranslated region of a protein kinase gene (MT-PK).' The kinetics of this process is influenced by the sex of the transmitting parent and size of the parental allele.2 Congenital DM (CDM) occurs almost always with maternal transmission. Only two patients with CDM have proven paternal inheritance.5' Maternal transmission is considered to be the result of a large intergenerational increase of the CTG repeat size,7 while repeat length contractions are more likely inherited if the mutated allele is of paternal origin.8 However, the range of expansions is wider for alleles transmitted by fathers with fewer than 100 repeats (range 41 to 95).9 This has suggested a male bias in the generation of new contracted or expanded DM alleles.'° Carey et all' described an unusual segregation of the MT-PK alleles with a CTG number > 19 in healthy persons heterozygous for repeats in the wild type size range, and suggested the possibility of meiotic drive at the DM locus

Y-linked suppressors of the sex-ratio trait in Drosophila mediopunctata

4412
Decarvalho, ABK, L. B.,  Heredity,  73:573-579. 1994-01-10 00:00:00.
X-linked meiotic drive causing female-biased progenies is known to occur in nine Drosophila species and is called 'sex-ratio'. In D. mediopunctata this trait is associated with the X:21 chromosome inversion and has variable expression. We describe here a powerful Y-linked suppressor system of sex-ratio expression in this species. There are two types of Y chromosomes (suppressor and nonsuppressor) and two types of X:21 chromosomes (suppressible and unsuppressible). Sex-ratio expression is suppressed in males with the 21 (suppressible)/Y-suppressor genotype, whereas the remaining three genotypes produce female-biased progenies.

The evolution of lethals in the t-haplotype system of the mouse

4411
Charlesworth, B,  Proceedings of the Royal Society B-Biological Sciences,  258:101-107. 1994-01-09 00:00:00.
The evolution of lethal haplotypes in the t-haplotype segregation distortion system of Mus is examined by mathematical and computer models. The models assume that there is reproductive compensation for the loss of lethal embryos, such that the net reproductive success of a female is not reduced in proportion to the frequency of lethal offspring which she produces. The initial population consists of a mixture of wildtype and homozygous male-sterile t-haplotypes. The failure of sterile males to reproduce may cause a higher fitness cost to mothers heterozygous for t-haplotypes than does elimination of a recessive lethal. Under certain conditions, a recessive lethal will spread and come to a polymorphic equilibrium. Wildtype, lethal and non-lethal haplotypes are all present at this equilibrium. Ifa second lethal mutation arises on a non-lethal t-haplotype in such an equilibrium population, it will increase in frequency and eventually displace the non-lethal t-haplotypes. A third lethal t-haplotype introduced at a low frequency into an equilibrium with two lethals can sometimes be selected for, although this is less likely if compensation is strong. The theoretical predictions are compared with data on natural populations.

Hypothetical sisterkiller

4409
Butcher, DLD, H. W.,  Nature,  369:26-26. 1994-01-07 00:00:00.
It was premature of Hurst in his News and Views article I to accept Haig's claim2 that a hypothetical meiotic drive element, SisterKiller, can lead to evolution from one-step to multi-step meiosis. The basis of Haig's claim is that a SisterKiller allele that causes a gamete to kill its sister gamete can invade and go to fixation in a population using one-step meiosis, whereas in a population using multi-step meiosis, Sister Killer cannot invade. Hurst concludes that SisterKiller could have caused the evolution of multi-step meiosis. The conditions under which this is true are more restrictive than Haig suggests.

Bewildering Bs – An impression of the 1st B-chromosome conference

4408
Beukeboom, LW,  Heredity,  73:328-336. 1994-01-06 00:00:00.
Ever since their first discovery B chromosomes have attracted attention. Why are they so appealing? The standard chromosomes of an organism are A chromosomes; B chromosomes are extra to this normal complement. In the B chromosome 'bible' (Jones & Rees, 1982) Bs are defined as dispensable supernumerary chromosomes that are not homologous and do not pair with A chromosomes. They have been further characterized as (1) morphologically different from As (usually smaller), (2) being inherited in a nonMendelian fashion, (3) not (or only rarely) having nucleolus organisers, (4) often displaying nondisjunction at anaphase of mitosis resulting in frequencies varying between organs in the same individual, (5) reducing fertility and growth when present in high numbers, and (6) carrying no genes with major effects. These features of Bs were recently discussed at an international conference and the main ideas presented by the participants are reported here. From 21 to 25 September 19

Eradication of the screwworm from Libya using the sterile insect technique

25558
M. Vargas-Terán, B. S. Hursey and E. P. Cunningham,  Parasitology Today,  10:119-122. 1994-01-01 09:06:27.
The introduction in 1988 of the New World screwworrn into Libya presented a serious threat to the livestock and wildlife sectors of the African continent Mediterranean and the region. In this article, MoisPs Vargas-Terin, Brian 8. Hursey and Edward P. Cunningham describe the action taken to determine the extent of the problem, to prevent the spread of the infestation and to eradicate the fly from the region using the sterile insect technique. New World screwworm hominivorax; myiasis is caused by the larval stage of the fly (Cochliomyia Coquerel) infesting the tissues of living animals. It is an obligate parasite and the female may oviposit in any wound or abrasion in mammals, including humans. Its natural distribution extends from the state of Minnesota, USA, southwards as far as Buenos Aires, A.rgentina, and includes the Caribbean region.

The Segregation Distorter (SD) complex and the accumulation of deleterious genes in laboratory strains of Drosophila melanogaster

4423
Dominguez, AS, E.; Albornoz, J.; Gutierrez, A.,  Theoretical and Applied Genetics,  87:479-486. 1993-01-21 00:00:00.
Segregation Distorter (SD) associated with the second chromosome of D. melanogaster is found in nature at equilibrium frequencies lower than 5%. We report extremely high frequencies of SD (30-50%) in two selected strains, established in 1976, and show it to be responsible for the accumulation of deleterious genes in chromosome II. Samples of chromosomes extracted over a 4-year period were characterized with respect to distortion, sensitivity, lethality, sterility, and inversions. SD chromosomes were inversion-free as they have been shown to be in the Mediterranean area. The cosmopolitan inversion In(2L)t was found associated with SD+ chromosomes. Lines polymorphic for SD have accumulated linked lethal and female-sterile genes approaching a near balanced system. It is proposed that deleterious genes linked in coupling to SD were accumulated by the balancing effect of distortion, while drift and restricted recombination account for the accumulation of deleterious genes linked in repulsion by a mechanism similar to Muller's ratchet. Our results should not be viewed as a particular case as SD chromosomes associated with detrimental genes and inversions are present in almost all populations around the world. The system could evolve in the way we describe whenever equilibrium conditions are broken down in small populations and lead to an increase in SD frequency.

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