An estimate of heterosis in<i>Drosophila melanogaster</i>

Ja, Sved

doi:10.1017/s0016672300012453

Cited by 95 publications

(72 citation statements)

References 7 publications

(1 reference statement)

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“…The rationale behind this experiment is outlined by Sved and Ayala (1970) and has been successfully applied by Bijlsma et al (1999). In short, balancer homozygotes are lethal and the wildtype homozygotes may also have a decreased fitness because of inbreeding depression.…”

Section: Balancer Chromosome Introgression Experimentsmentioning

confidence: 99%

Dynamics of genetic rescue in inbred Drosophila melanogaster populations

et al. 2010

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Genetic rescue has been proposed as a management strategy to improve the fitness of genetically eroded populations by alleviating inbreeding depression. We studied the dynamics of genetic rescue in inbred populations of Drosophila. Using balancer chromosomes, we show that the force of heterosis that accompanies genetic rescue is large and allows even a recessive lethal to increase substantially in frequency in the rescued populations, particularly at stress temperatures. This indicates that deleterious alleles present in the immigrants can increase significantly in frequency in the recipient population when they are in linkage disequilibrium with genes responsible for the heterosis. In a second experiment we rescued eight inbred Drosophila populations with immigrants from two other inbred populations and observe: (i) there is a significant increase in viability both 5 and 10 generations after the rescue event, showing that the increase in fitness is not transient but persists long-term. (ii) The lower the fitness of the recipient population the larger the fitness increase. (iii) The increase in fitness depends significantly on the origin of the rescuers. The immigrants used were fixed for a conditional lethal that was mildly deleterious at 25°C but lethal at 29°C. By comparing fitness at 25°C (the temperature during the rescue experiment) and 29°C, we show that the lethal allele reached significant frequencies in most rescued populations, which upon renewed inbreeding became fixed in part of the inbred lines. In conclusion, in addition to the fitness increase genetic rescue can easily result in a substantial increase in the frequency of mildly deleterious alleles carried by the immigrants. This can endanger the rescued population greatly when it undergoes recurrent inbreeding. However, using a sufficient number of immigrants and to accompany the rescue event with the right demographic measures will overcome this problem. As such, genetic rescue still is a viable option to manage genetically eroded populations.

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Section: Balancer Chromosome Introgression Experimentsmentioning

confidence: 99%

Dynamics of genetic rescue in inbred Drosophila melanogaster populations

et al. 2010

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“…14). For example, in natural populations of Drosophila, approximately 30% of chromosomes carry a recessive lethal, and chromosomes that do not carry a recessive lethal suffer from at least 30% depression in homozygous fitness (15)(16)(17)(18)(19)(20)(21)(22)(23)(24). These data suggest that many, if not most, deleterious mutations are likely to be fully or partially recessive, and such mutations can have a moderate to strong fitness effect in the homozygote.…”

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confidence: 99%

Obstruction of adaptation in diploids by recessive, strongly deleterious alleles

Assaf¹,

Petrov²,

Blundell

2015

Proc. Natl. Acad. Sci. U.S.A.

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Recessive deleterious mutations are common, causing many genetic disorders in humans and producing inbreeding depression in the majority of sexually reproducing diploids. The abundance of recessive deleterious mutations in natural populations suggests they are likely to be present on a chromosome when a new adaptive mutation occurs, yet the dynamics of recessive deleterious hitchhikers and their impact on adaptation remains poorly understood. Here we model how a recessive deleterious mutation impacts the fate of a genetically linked dominant beneficial mutation. The frequency trajectory of the adaptive mutation in this case is dramatically altered and results in what we have termed a "staggered sweep." It is named for its threephased trajectory: (i) Initially, the two linked mutations have a selective advantage while rare and will increase in frequency together, then (ii), at higher frequencies, the recessive hitchhiker is exposed to selection and can cause a balanced state via heterozygote advantage (the staggered phase), and (iii) finally, if recombination unlinks the two mutations, then the beneficial mutation can complete the sweep to fixation. Using both analytics and simulations, we show that strongly deleterious recessive mutations can substantially decrease the probability of fixation for nearby beneficial mutations, thus creating zones in the genome where adaptation is suppressed. These mutations can also significantly prolong the number of generations a beneficial mutation takes to sweep to fixation, and cause the genomic signature of selection to resemble that of soft or partial sweeps. We show that recessive deleterious variation could impact adaptation in humans and Drosophila.I n diploids, the fitness effect of having a single copy of a mutation depends not only on the mutation's selective effect, s, but also on its heterozygous effect, h. A fully recessive mutation (h = 0) is hidden in the heterozygote (hs = 0), and a fully dominant mutation (h = 1) is completely exposed (hs = s). Although it is generally agreed that beneficial mutations that reach fixation tend to be dominant (i.e., h ≥ 0.5) (1, 2), both empirical data and theoretical models (3-6) suggest that many strongly and even moderately deleterious mutations are likely to be recessive (i.e., h < 0.5). For example, studies of de novo mutations from both mutation accumulation and mutagenesis experiments in Drosophila melanogaster, Saccharomyces cerevisiae, and Caenorhabditis elegans have repeatedly found that strongly deleterious mutations tend to be completely recessive (h ≈ 0) and more weakly deleterious mutations tend to be partially recessive (h ≈ 0.1) (7-13). Furthermore, studies of natural populations have found that inbreeding depression is pervasive across sexually reproducing diploids and is mainly caused by recessive deleterious variation (reviewed in ref. 14). For example, in natural populations of Drosophila, approximately 30% of chromosomes carry a recessive lethal, and chromosomes that do not carry a recessive lethal suffer fro...

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“…+ heterozygote is detected in cages of low modifier background (averages of fertility estimates were 0.63 and 0.44 in cages L1 and L2, respectively). This is not an unusual result because there are many cases in the literature where fertility selection is an important component of total selection (Polivanov & Anderson, 1969;Sved & Ayala, 1970;Sved, 1971;Bundgaard & Christiansen, 1972;Anderson et al, 1979). On the other hand, our experimental design for fitness estimation splits total fitness into a component of preadult survival or egg-to-adult viability and into an adult fitness component or fertility.…”

Section: Discussionmentioning

confidence: 82%

“…For fitness estimation the zygotic frequency of Ba! + heterozygotes was corrected as this frequency is estimated at the adult stage rather than the egg stage (see Sved, 1971). The null hypothesis of no selective differences between Ba!+ and +/+ genotypes was tested by means of two different statistical approaches: an approximate significance test based on the x2 distribution (see Materials and methods) and the 95 per cent bootstrap confidence intervals (Efron & Tibshirani, 1986).…”

Section: Discussionmentioning

confidence: 99%

Measuring selective effects of modifier gene polymorphisms on the Bare locus of Drosophila subobscura

Álvarez

1996

Heredity

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An attempt to quantify the effects of modifier gene polymorphisms on the operation of natural selection on a major locus has been carried out. The modifier system we have investigated is constituted by a set of polygenic modifier loci affecting the morphological expression of the Bare (Ba) bristle mutant of Drosophila subobscura. Ba is a dominant mutant that is lethal in homozygous condition and both the polygenic modifiers and Ba are located on the 0 chromosome of this species. Experimental populations were founded with Ba! + individuals and two different types of populations were started according to their modifier genetic background: populations with wild 0 chromosomes of either high or low modifier effect (cages H and L, respectively). Fitness estimates (total fitness, viability and fertility) for genotypes of the Ba locus were obtained under the two different modifier backgrounds. In the populations with high modifier background the total fitness of the Ba! + heterozygote was very similar to that of the +/+ homozygote (fitness equal to 1). However, in cages with low modifier background a strong selection against the Ba! + heterozygote was detected (average of total fitnesses over generations was 0.66±0.10), and fertility appears to be the fitness component responsible for this effect (mean fertility was 0.55 0.08). These findings demonstrate that modifier gene polymorphisms affecting the expression of the Ba mutant may be associated with large selective effects on the major locus.

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An estimate of heterosis inDrosophila melanogaster

Cited by 95 publications

References 7 publications

Dynamics of genetic rescue in inbred Drosophila melanogaster populations

Dynamics of genetic rescue in inbred Drosophila melanogaster populations

Obstruction of adaptation in diploids by recessive, strongly deleterious alleles

Measuring selective effects of modifier gene polymorphisms on the Bare locus of Drosophila subobscura

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