Phenotypic response to selection for traits with direct and maternal components when generations overlap

Summary Prediction of response to selection for traits with direct and maternal components is described for discrete and overlapping generations. Expected phenotypic response is the sum of direct and maternal contributions, the latter having a genetic and an environmental component. With overlapping generations the selection differentials achieved on these components are added to respective updated vectors containing age-sex distributions with values of previous selection rounds. An example demonstrates that in the early stages, results may be considerably affected by environmental correlations between direct and maternal effects. The method could be helpful in interpreting phenotypic changes in a population selected for traits with maternal effects.     

Selection in a cycling population: differential response among skeletal traits

Abstract Population density cycles influence phenotypic evolution through both density‐dependent selection during periods of high density and through enhanced genetic drift during periods of low density. We investigated the response of different phenotypic traits to the same density cycles in a population of the yellow‐necked mouse, Apodemus flavicollis, from Bia?owieza National Park in Poland. We examined nonmetric skull traits, skull and mandible size, skull and mandible shape, and transferrin allele frequencies. We found that all of the traits changed significantly over the seven‐year study period. The greatest changes in nonmetric traits and mandible size occurred during periods of increasing density, and the magnitude of changes in skull and mandible shape was correlated with the magnitude of density changes. Frequencies of transferrin alleles changed the most when population density was in decline. Changes among the five phenotypic traits were generally uncorrelated with one another, except for skull and mandible shape. Nonmetric traits were selectively neutral when assessed with Q_ST/F_ST analysis, whereas mandible size, mandible shape, and skull shape showed evidence of fairly strong selection. Selection on skull size was weak or nonexistent. We discuss how different assumptions about the genetic components of variance affect Q_ST estimates when phenotypic variances are substituted for genetic ones. We also found that change in mandible size, mandible shape, skull size, and skull shape were greater than expected under a neutral model given reasonable assumptions about heritability and effective population size.     

Parallel evolution and inheritance of quantitative traits

Parallel phenotypic evolution, the independent evolution of the same trait in closely related lineages, is interesting because it tells us about the contribution of natural selection to phenotypic evolution. Haldane and others have proposed that parallel evolution also results from a second process, the similarly biased production of genetic variation in close relatives, an idea that has received few tests. We suggest that influence of shared genetic biases should be detectable by the disproportionate use of the same genes in independent instances of parallel phenotypic evolution. We show how progress in testing this prediction can be made through simple tests of parallel inheritance of genetic differences: similar additive, dominance, and epistasis components in analysis of line means and similar effective numbers of loci. We demonstrate parallel inheritance in two traits, lateral plate number and body shape, in two lineages of threespine stickleback that have adapted independently to freshwater streams on opposite sides of the Pacific Ocean. Notably, reduction of plate number in freshwater involves a substitution at the same major locus in both lineages. Our results represent only a first step in the study of the genetics of parallel phenotypic evolution in sticklebacks. Nevertheless, we have shown how such studies can be employed to test the genetic hypothesis of parallel evolution and how study of parallel evolution might yield insights into the roles of both selection and genetic constraint in phenotypic evolution.     

Paternal inheritance of chloroplast DNA and maternal inheritance of mitochondrial DNA in loblolly pine

Summary The inheritance of organelle DNAs in loblolly pine was studied by using restriction fragment length polymorphisms. Chloroplast DNA from loblolly pine is paternally inherited in pitch pine x loblolly pine hybrids. Mitochondrial DNA is maternally inherited in loblolly pine crosses. The uniparental inheritance of organelle genomes from opposite sexes within the same plant appears to be unique among those higher plants that have been tested and indicates that loblolly pine, and possibly other conifers, must have special mechanisms for organelle exclusion or degradation or both. This genetic system creates an exceptional opportunity for the study of maternal and paternal genetic lineages within a single species.     

Mode of inheritance of primary metabolic traits in tomato

To evaluate components of fruit metabolic composition, we have previously metabolically phenotyped tomato (Solanum lycopersicum) introgression lines containing segmental substitutions of wild species chromosome in the genetic background of a cultivated variety. Here, we studied the hereditability of the fruit metabolome by analyzing an additional year's harvest and evaluating the metabolite profiles of lines heterozygous for the introgression (ILHs), allowing the evaluation of putative quantitative trait locus (QTL) mode of inheritance. These studies revealed that most of the metabolic QTL (174 of 332) were dominantly inherited, with relatively high proportions of additively (61 of 332) or recessively (80 of 332) inherited QTL and a negligible number displaying the characteristics of overdominant inheritance. Comparison of the mode of inheritance of QTL revealed that several metabolite pairs displayed a similar mode of inheritance of QTL at the same chromosomal loci. Evaluation of the association between morphological and metabolic traits in the ILHs revealed that this correlation was far less prominent, due to a reduced variance in the harvest index within this population. These data are discussed in the context of genomics-assisted breeding for crop improvement, with particular focus on the exploitation of wide biodiversity.     

The maternal inheritance of proteins synthesized in mammalian mitochondria

Interspecific variations between the proteins synthesized in the mitochondria of two closely related mammalian species were demonstrated to be maternally inherited by examination of their hybrid progeny. This, in accordance with the documented uniparental inheritance of mitochondrial DNA (mtDNA) would indicate that the latter codes for the products of mitochondrial translation.     

Ovary-autonomous maternal inheritance at a developmental locus in Drosophila

The sex-linked temperature-sensitive mutation shibire^ts of Drosophila melanogaster shows a maternal effect causing embryonic lethality at 29°C. The maternal influence is due to gene action autonomous to the ovary. Embryos carrying the paternally derived wild-type gene can survive at 29°C but only if heat pulses are begun at least 9 hr after oviposition. The paternal rescue is presumably due to zygotic gene action at this locus beginning part way through embryogenesis. A maternal wild-type genome, however, can produce shi embryos that have sufficient shi⁺ product to support embryogenesis up to the hatching stage even at 29°C.     

Paternal inheritance of chloroplast DNA and maternal inheritance of mitochondrial DNA in the genus Actinidia

PCR amplification of four chloroplast DNA (cpDNA) and two mitochondrial DNA (mtDNA) regions followed by restriction of the amplified products was used to identify restriction fragment length polymorphisms in 21 Actinidia taxa. Subsequently, the mode of organelle inheritance was investigated in both interspecific and intraspecific controlled crosses made between genotypes showing different cpDNA and/or mtDNA haplotypes. Fifty-six seedlings produced from three interspecific crosses, including in one case the pseudo reciprocal (different genotypes of the same species used as opposite parents), were checked for cpDNA inheritance, and 102 seedlings from the same interspecific crosses and 32 seedlings from two intraspecific crosses within the species A. deliciosa were checked for mtDNA inheritance. In all cases, cpDNA was inherited from the father and mtDNA was inherited from the mother. Maternal inheritance of mtDNA was expected, being the rule in plants, but A. deliciosa is the first genus in angiosperms for which a widespread and strictly paternal inheritance of cpDNA has been reported. Transmission of chloroplastic and mitochondrial genomes through opposite parents provides an exceptional opportunity for studying the paternal and maternal genetic lineages of species in the genus Actinidia.     

Selection for male-enforced uniparental cytoplasmic inheritance

In most sexually reproducing species, including humans, mitochondria and other cytoplasmic elements are uniparentally (usually maternally) inherited. This phenomenon is of broad interest as a mechanism for countering the proliferation of selfish mitochondria. Uniparental inheritance can be enforced either by the female gametes excluding male cytoplasm or male gametes excluding their own from the zygote. Previous studies have shown that male-enforced uniparental inheritance is unlikely to evolve as a primary mechanism, because unlike female enforcement, the positive linkage disequilibrium between the modifier for eliminating the gamete’s own mitochondria and a wild-type mitochondrial complement is broken from one generation to the next. However, it has been proposed that with a sufficiently high mutation rate and strong selection, elimination of the gamete’s own mitochondria could be favored by selection. In this article, a series of numerical simulations confirm that this is indeed the case, although the conditions where male enforcement is favored are quite restrictive. Specifically, in addition to a high mutation rate to selfish mitochondria and strong selection against them, the cost of uniparental inheritance must be negligible.     

Studies on maternal inheritance in polyploid wheats with cytoplasmic DNAs as genetic markers

Summary Restriction fragment patterns of DNA fragments obtained after EcoRI cleavage of chloroplastic (cp) and mitochondrial (mt) DNAs isolated from different wheat species were compared. T. aestivum, T. timopheevi, Ae. speltoides, Ae. sharonensis and T. urartu gave species specific mt DNA patterns. Consequently, the cytoplasmic genomes of wheat cannot have originated from contemporary Ae. speltoides, Ae. sharonensis and T. urartu species. It is shown that cp and mt DNAs of Ae. ventricosa, a tetraploid used to transfer eyespot resistance into T. aestivum, contains cp and mt DNAs differing from DNAs isolated from T. aestivum and other wheats. In contrast, the cytoplasmic DNAs of Ae. ventricosa and Ae. squarrosa reveal an important homology, suggesting that Ae. squarrosa was the female parent of Ae. ventricosa. Disomic addition lines (T. aestivum — Ae. ventricosa) in both Ae. ventricosa cytoplasm and T. aestivum cytoplasm contained cytoplasmic DNAs identical to those of the maternal parent. Restriction patterns of the cp and mt DNAs isolated from eight lines of Triticale differing in their cytoplasm have been compared to those of the maternal parent. A strict maternal inheritance has been observed in each case.     

Unisexual reproduction: Either maternal or paternal inheritance

Parthenogenesis is usually recognized as the most accepted mechanism of cloning, i.e., reproduction without genetic recombination. Transfer from bisexual to parthenogenetic propagation causes the appearance of all-female populations, races, and species. It was ascertained in natural populations of numerous of reptile and insect species. Clonal and hemiclonal species of fishes and amphibians propagate by means of gynogenesis and hybridogenesis. Less known are instances of androgenesis found in some insects and mollusks. In this case offspring develops only under control of male genes supplied by spermatozoa. Mother’s genes included into the egg nucleus have to be entirely lost. Androgenesis may be called mirroring of parthenogenesis.     

The placental gateway of maternal transgenerational epigenetic inheritance

While much of our understanding of genetic inheritance is based on the genome of the organism, it is becoming clear that there is an ample amount of epigenetic inheritance, which though reversible, escapes erasing process during gametogenesis and goes on to the next generation. Several examples of transgenerational inheritance of epigenetic features with potential impact on embryonic development and subsequent adult life have come to light. In placental mammals, the placenta is an additional route for epigenetic information flow. This information does not go through any meiotic reprogramming and is, therefore, likely to have a more profound influence on the organism. This also has the implication of providing epigenetic instructions for several months, which is clearly a maternal advantage. Although less well-known, there is also an impact of the embryo in emitting genetic information to the maternal system that remains well beyond the completion of the pregnancy. In this review, we discuss several factors in the context of the evolution of this mammal-specific phenomenon, including genomic imprinting, micromosaicism, and assisted reproduction. We also highlight how this kind of inheritance might require attention in the modern lifestyle within the larger context of the evolutionary process.     

Evidence for maternal inheritance of mitochondrial DNA in allotetraploid.

The complete mitochondrial DNA (mtDNA) sequences of the allotetraploid and red crucian carp were determined in this paper. We compared the complete mtDNA sequences between the allotetraploid and its female parent red crucian carp, and between the allotetraploid and its male parent common carp. The results indicated that the complete mtDNA nucleotide identity (99.7%) between the allotetraploid and its female parent red crucian carp was higher than that (89.0%) between the allotetraploid and its male parent common carp. Moreover, the analysis on the start and stop codons, overlaps and spacers, and phylogeny of the mt genomes indicated the genetic relationship between the allotetraploid and its female parent red crucian carp was closer than that between the allotetraploid and its male parent common carp. Our results indicated that the allotetraploid mt genome was strictly maternally inherited. Through maternal inheritance, the mt genome in the F(11) allotetraploid displayed extremely high similarity to that in the female parent red crucian carp after 11 generations (from F(1) to F(11) hybrids). Such results indicated that the F(11) allotetraploid possessed the stable inheritance characteristic. Thus the tetraploid stocks possessed the good base to form a new tetraploid species in the future. Since the establishment of the new tetraploid stocks has the great significance in analyzing evolutionary theory of vertebrate and in improving aquaculture industry, analysis of the mt genome and the elucidation of the variation of the mt genome in the allotetraploid and its parents proved that it was a useful genetic marker to monitor the variations in the progeny of the crosses.     

Passing the message on: inheritance of epigenetic traits

Epigenetic modifiers play an important role in genome organization, stability and the control of gene expression. Three research groups that are exploring the transfer of epigenetic information between generations have recently published papers. Mary Alleman et al. have shown that RNA-directed chromatin changes mediate paramutation in maize, and Minoo Rassoulzadegan et al. have demonstrated that RNA also plays a role in paramutation in mice. A new aspect of epigenetic regulation has been revealed by Jean Molinier et al. - they have demonstrated that the memory of exposure to stress is transferred through several generations.     

Simple inheritance of key traits distinguishing maize and teosinte

The segregation of key traits distinguishing maize and teosinte was analyzed in three F₂ and three backcross populations derived from crosses of the modern maize inbred T232 withZea mays ssp.parviglumis. These traits were (i) paired vs. single female spikelets; (ii) two-ranked vs. many-ranked ears; (iii) non-indurated vs. indurated glumes; (iv) inclination of the kernels toward the rachis, and (v) distichous vs. polystichous central staminate spike. All traits showed a simple mode of inheritance except for paired female spikes, which appeared to be controlled by two genes. The loci controlling these major changes were mapped with RFLP markers to four chromosomal regions. These results support the suggestion that maize became differentiated from teosinte with as few as five major gene changes.This paper is dedicated to the memory of Professor Jean Pernes     

The inheritance of organogenic response in melon

Previous studies have demonstrated variation in organogenic competence among plants within a population ofCucumis melo. In order to determine if leaf explant response is under genetic control, we investigated the distribution of the shoot regeneration frequency in F₁ and F₂ generations from parents representing extreme values forin vitro organogenic response. Results suggest a genetic model with two genes, partial dominance, independent segregation and similar effects for both genes.     

Strict paternal inheritance of chloroplast DNA and maternal inheritance of mitochondrial DNA in intraspecific crosses of kiwifruit

 Previous studies have established that chloroplasts are inherited paternally in Actinidia interspecific crosses. However, fertilisation problems in interspecific crosses may affect the transmission of organelles. Six female clones, i.e. ‘Abbott’, ‘Bruno’, ‘Greensill’, ‘Hayward’, ‘Jones’, ‘Monty’, and four male clones were used to identify cpDNA polymorphisms within the cultivated kiwifruit species A. deliciosa. The restriction patterns by HpaII of a chloroplast fragment amplified by PCR with a pair of universal primers revealed a polymorphism at the intraspecific level. The inheritance of cpDNA in 143 seedlings from three intraspecific crosses in kiwifruit (Actinidia deliciosa) was studied. All offspring displayed the restriction pattern of the paternal parent, indicating that maternal inheritance of cpDNA in kiwifruit is rare at best. Strict maternal inheritance of mtDNA was confirmed in the same crosses used to investigate cpDNA transmission. Studies of cytoplasmic inheritance in the Actinidia genus represent to date the best documented report of differential organelle inheritance of cpDNA and mtDNA in angiosperms. Received: 10 November 1998 / Accepted: 14 December 1998     

Selection explanations of token traits

The “negative view” is the claim that natural selection cannot explain why a particular individual has one trait, rather than another. Here, I modify an example from Lewens (2001) to show that this claim is sometimes false. I then advance a variation on the negative view. It is the claim that selection at the organism level within a lineage cannot explain why a particular individual in that lineage has one allele, rather than another. This formulation better describes the explanatory role of selection.