Reinforcement and sex linkage

We present a general model for the effect of sex linkage on the evolution of reinforcement of mating preferences on an island. We find that the level of reinforcement can vary up to 80% depending on the mode of inheritance of the female preference and male trait. When reinforcement is driven mainly by selection in the male trait and intrinsic hybrid incompatibilities are weak, sex-linked preferences and autosomal male traits are the most conducive to reinforcement, whereas autosomal preferences and X-linked traits are the least. Surprisingly, the effect of mode of inheritance on reinforcement is poorly predicted by its effect on the genetic correlation between the male trait and female preference. Sex-linkage of genetic incompatibility loci increases reinforcement, though this is not due solely to the occurrence of Haldane's rule. We find that reinforcement can lead to complete reproductive isolation in some cases but not others and that the mode of inheritance can determine which outcome occurs.     

Genomic analysis I: inheritance units and genetic selection in the rapid discovery of locus linked DNA markers.

We propose, and test using a Monte-Carlo analysis (a computer-based numerical analysis using a random number generator), a novel and efficient method to obtain sets of DNA markers linked to any inherited genetic locus. The method consists of a targeted search that is based on the common inheritance among members of an outbred pedigree, of discrete chromosome lengths, which we call inheritance units, to obtain DNA markers linked to the locus. In cases where two individuals inherit the same trait through two different lines of descent from a common ancestor, the set of inheritance units in each of the two genomes includes an inheritance unit that is identical in both individuals for a substantial distance on both sides of the DNA sequence which confers the trait. The power of the technique derives from the genetic selection that reduces the size and number of the inheritance units as the generational distance between the two individuals being compared increases.     

Homology across inheritance systems

Recent work on inheritance systems can be divided into inclusive conceptions, according to which genetic and non-genetic inheritance are both involved in the development and transmission of nearly all animal behavioral traits, and more demanding conceptions of what it takes for non-genetic resources involved in development to qualify as a distinct inheritance system. It might be thought that, if a more stringent conception is adopted, homologies could not subsist across two distinct inheritance systems. Indeed, it is commonly assumed that homology relations cannot survive a shift between genetic and cultural inheritance systems, and substantial reliance has been placed on that assumption in debates over the phylogenetic origins of hominin behavioral traits, such as male-initiated intergroup aggression. However, in the homology literature it is widely accepted that a trait can be homologous—that is, inherited continuously in two different lineages from a single common ancestor—despite divergence in the mechanisms involved in the trait’s development in the two lineages. In this paper, we argue that even on an extremely stringent understanding of what it takes for developmental resources to form a separate inheritance system, homologies can nonetheless subsist across shifts between distinct inheritance systems. We argue that this result is a merit of this way of characterizing what it is to be an inheritance system, that it has implications for adjudicating between alternative accounts of homology, and that it offers an important cautionary lesson about how (not) to reason with the homology concept, particularly in the context of cultural species.     

An Approximate Model of Polygenic Inheritance

The finite polygenic model approximates polygenic inheritance by postulating that a quantitative trait is determined by n independent, additive loci. The 3(n) possible genotypes for each person in this model limit its applicability. CANNINGS, THOMPSON, and SKOLNICK suggested a simplified, nongenetic version of the model involving only 2n + 1 genotypes per person. This article shows that this hypergeometric polygenic model also approximates polygenic inheritance well. In particular, for noninbred pedigrees, trait means, variances, covariances, and marginal distributions match those of the ordinary finite polygenic model. Furthermore as n -> &, the trait values within a pedigree collectively tend toward multivariate normality. The implications of these results for likelihood evaluation under the polygenic threshold and mixed models of inheritance are discussed. Finally, a simple numerical example illustrates the application of the hypergeometric polygenic model to risk prediction under the polygenic threshold model.     

Towards robust evolutionary inference with integral projection models

Integral projection models (IPMs) are extremely flexible tools for ecological and evolutionary inference. IPMs track the distribution of phenotype in populations through time, using functions describing phenotype‐dependent development, inheritance, survival and fecundity. For evolutionary inference, two important features of any model are the ability to (i) characterize relationships among traits (including values of the same traits across ages) within individuals, and (ii) characterize similarity between individuals and their descendants. In IPM analyses, the former depends on regressions of observed trait values at each age on values at the previous age (development functions), and the latter on regressions of offspring values at birth on parent values as adults (inheritance functions). We show analytically that development functions, characterized this way, will typically underestimate covariances of trait values across ages, due to compounding of regression to the mean across projection steps. Similarly, we show that inheritance, characterized this way, is inconsistent with a modern understanding of inheritance, and underestimates the degree to which relatives are phenotypically similar. Additionally, we show that the use of a constant biometric inheritance function, particularly with a constant intercept, is incompatible with evolution. Consequently, current implementations of IPMs will predict little or no phenotypic evolution, purely as artefacts of their construction. We present alternative approaches to constructing development and inheritance functions, based on a quantitative genetic approach, and show analytically and through an empirical example on a population of bighorn sheep how they can potentially recover patterns that are critical to evolutionary inference.     

Estimation and visualization of identity-by-descent within pedigrees simplifies interpretation of complex trait analysis

Linkage analysis identifies markers that appear to be co-inherited with a trait within pedigrees. The inheritance of a chromosomal segment may be probabilistically reconstructed, with missing data complicating inference. Inheritance patterns are further obscured in the analysis of complex traits, where variants in one or more genes may contribute to phenotypic variation within a pedigree. In this case, determining which relatives share a trait variant is not simple. We describe how to represent these patterns of inheritance for marker loci. We summarize how to sample patterns of inheritance consistent with genotypic and pedigree data using gl_auto, available in MORGAN v3.0. We describe identification of classes of equivalent inheritance patterns with the program IBDgraph. We finally provide an example of how these programs may be used to simplify interpretation of linkage analysis of complex traits in general pedigrees. We borrow information across loci in a parametric linkage analysis of a large pedigree. We explore the contribution of each equivalence class to a linkage signal, illustrate estimated patterns of identity-by-descent sharing, and identify a haplotype tagging the chromosomal segment driving the linkage signal. Haplotype carriers are more likely to share the linked trait variant, and can be prioritized for subsequent DNA sequencing.     

Linkage analysis and the inheritance of arches in a Habbanite isolate.

A pedigree and linkage analysis was performed on a corrected version of the Habbanite pedigree 2 of Slatis et al. [1]. The trait "arch on any digit" was examined for major gene inheritance and possible linkage to several blood and serum group markers. The results confirm the proposed dominant major gene inheritance of this trait with almost complete penetrance. In addition, the analysis suggests linkage with the haptoglobin locus with evidence against linkage with Pl and Rhesus. These results are of particular interest in view of recently reported dermatoglyphic associations with haptoglobin.     

The use of exclusive trios in human pedigrees to determine autosomal or X-linked dominance or recessiveness

Four rules of judgement, each involving one child and its parents, can rule out one common mode of inheritance each, namely dominance, or recessiveness, autosomal or sex-linkage. A large pedigree usually provides three different groups of ? particular child and its parents. Each such trio may rule out one particular mode of inhe itance. When both parents show a trait but one daughter does not, the trait cannot be recessive. When no parent shows the trait but one son or daughter does, the trait cannot be dominant. Again, if a father shows a trait but his daughter and her mother do not show it, the trait cannot be sex-linked dominant. And when a mother shows a trait, but her son and his father do not, the trait cannot be sex-linked recessive. A pedigree having three of these four different sets of “parents-and-child” groups, rules out three modes of inheritance for the trait in question, and thereby confirms that the mode of inheritance for the trait is, as a rule, the single remaining mode of the four.     

Estimating the power of a proposed linkage study for a complex genetic trait.

Many genetic traits have complex modes of inheritance; they may exhibit incomplete or age-dependent penetrance or fail to show any clear Mendelian inheritance pattern. As primary linkage maps for the human genome near completion, it is becoming increasingly possible to map these traits. Prior to undertaking a linkage study, it is important to consider whether the pedigrees available for the proposed study are likely to provide sufficient information to demonstrate linkage, assuming a linked marker is tested. In the current paper, we describe a computer simulation method to estimate the power of a proposed study to detect linkage for a complex genetic trait, given a hypothesized genetic model for the trait. Our method simulates trait locus genotypes consistent with observed trait phenotypes, in such a way that the probability to detect linkage can be estimated by sample statistics of the maximum lod score distribution. The method uses terms available when calculating the likelihood of the trait phenotypes for the pedigree and is applicable to any trait determined by one or a few genetic loci; individual-specific environmental effects can also be dealt with. Our method provides an objective answer to the question, Will these pedigrees provide sufficient information to map this complex genetic trait?     

Segregation distortion for seed testa color in Mungbean (Vigna radiata L. Wilcek)

Genetic segregation experiments with plant species are commonly used for understanding the inheritance of traits. A basic assumption in these experiments is that each gamete developed from megasporogenesis has an equal chance of fusing with a gamete developed from microsporogenesis, and every zygote formed has an equal chance of survival. If gametic and/or zygotic selection occurs whereby certain gametes or zygotic combinations have a reduced chance of survival, progeny distributions are skewed and are said to exhibit segregation distortion. In this study, inheritance data are presented for the trait seed testa color segregating in large populations (more than 200 individuals) derived from closely related mungbean (Vigna radiata L. Wilcek) taxa. Segregation ratios suggested complex inheritance, including dominant and recessive epistasis. However, this genetic model was rejected in favor of a single-gene model based on evidence of segregation distortion provided by molecular marker data. The segregation distortion occurred after each generation of self-pollination from F1 thru F7 resulting in F7 phenotypic frequencies of 151:56 instead of the expected 103.5:103.5. This study highlights the value of molecular markers for understanding the inheritance of a simply inherited trait influenced by segregation distortion.     

Why are most organelle genomes transmitted maternally?

Why the DNA‐containing organelles, chloroplasts, and mitochondria, are inherited maternally is a long standing and unsolved question. However, recent years have seen a paradigm shift, in that the absoluteness of uniparental inheritance is increasingly questioned. Here, we review the field and propose a unifying model for organelle inheritance. We argue that the predominance of the maternal mode is a result of higher mutational load in the paternal gamete. Uniparental inheritance evolved from relaxed organelle inheritance patterns because it avoids the spread of selfish cytoplasmic elements. However, on evolutionary timescales, uniparentally inherited organelles are susceptible to mutational meltdown (Muller's ratchet). To prevent this, fall‐back to relaxed inheritance patterns occurs, allowing low levels of sexual organelle recombination. Since sexual organelle recombination is insufficient to mitigate the effects of selfish cytoplasmic elements, various mechanisms for uniparental inheritance then evolve again independently. Organelle inheritance must therefore be seen as an evolutionary unstable trait, with a strong general bias to the uniparental, maternal, mode.     

质量性状和数量性状含义的辨析

植物或动物的性状一般分为质量性状和数量性状,而实际上,许多性状并不是绝对的质量性状或数量性状,而是同时受到一个或少数几个主基因和或数量性状多基因的控制.因此,在遗传学教学中,有必要对此类性状进行分析.为加深学生对此类性状的遗传及这两个概念的理解,通过性状次数分布图分析,结合最新的遗传学研究成果,对之进行了分析和讨论.     

Possibility of major gene control over scale E of Cattel's test

The segregation analysis is made of inheritance of the E factor of the Cattell's 16PF Questionnaire on the basis of a population sample consisting of 108 free-structured pedigrees. The possibility of major gene control of inheritance for this quantitative trait is confirmed.     

The relative importance of genetic and nongenetic inheritance in relation to trait plasticity in Callosobruchus maculatus

A trait's response to natural selection will reflect the nature of the inheritance mechanisms that mediate the transmission of variation across generations. The relative importance of genetic and nongenetic mechanisms of inheritance is predicted to be related to the degree of trait plasticity, with nongenetic inheritance playing a greater role in the cross‐generational transmission of more plastic traits. However, this prediction has never been tested. We investigated the influence of genetic effects and nongenetic parental effects in two morphological traits differing in degree of plasticity by manipulating larval diet quality within a cross‐generational split‐brood experiment using the seed beetle Callososbuchus maculatus. In line with predictions, we found that the more plastic trait (elytron length) is strongly influenced by both maternal and paternal effects whereas genetic variance is undetectable. In contrast, the less plastic trait (first abdominal sternite length) is not influenced by parental effects but exhibits abundant genetic variance. Our findings support the hypothesis that environment‐dependent parental effects may play a particularly important role in highly plastic traits and thereby affect the evolutionary response of such traits.     

Evidence for a new major gene influencing meat quality in pigs

The present investigation primarily deals with the inheritance of a pigmeat quality trait, the Napole technological yield (RTN), a measure of cooked weight to fresh weight. This trait as well as lean percentage at 100 kg liveweight and fattening length from 20 to 100 kg liveweight were recorded on 3459 offspring from 67 sires and 433 dams, and 3052 offspring from 64 sires and 405 dams in Penshire (P66) and Pen Ar Lan (P77) composite lines respectively. The hypothesis of a major 2-allele locus contributing to RTN was tested by use of a segregation analysis method. Highly significant likelihood ratios (mixed vs. polygenic transmission models) lead us to conclude that a major gene RN- exerting an unfavourable effect on RTN is segregating in both lines. Maximum likelihood estimates of the parameters under the hypothesis of mixed (monogenic + polygenic) inheritance show that the difference between the means of the 2 homozygotes amounts to about 3 phenotypic standard deviations of the trait, whereas the complete dominance of RN- cannot be rejected. The frequency of RN- is about 0.6 in both lines. These results are discussed in connection with the previously reported 'Hampshire effect' on pigmeat quality, as the Hampshire breed is a common component of the foundation stock of the 2 composite lines under study.     

Manifestation of "hairy leaf" trait in mangel beet

New morphological trait, "Hairy leaf", of mangel beet has been picked out. Dominant character and monogenic inheritance of the trait were found. Comparative analysis of manifestation of this trait in mangel and sugar beets was done. It is shown that the gene of "hairiness" (Hl) in sugar beet is not allelic to the Hlvar gene in mangel beet. This trait can be used as a marker in selection-genetical investigation.     

How to model a complex trait. 1. General considerations and suggestions

Usually, when complex traits are at issue, not only are the loci of the responsible genes a priori unknown; the same also holds for the mode of inheritance of the trait, and sometimes even for the phenotype definition. The term mode of inheritance relates to both the genetic mechanism, i.e., the number of loci implicated in the etiology of the disease, and the genotype-phenotype relation, which describes the influence of these loci on the trait. Having an idea of the genetic model can crucially facilitate the mapping process. This holds especially in the context of linkage analysis, where an appropriate parametric model or a suitable nonparametric allele sharing statistic may accordingly be selected. Here, we review the difficulties with parametric and nonparametric linkage analysis when applied to multifactorial diseases. We address the question why it is necessary to adequately model a genetically complex trait in a linkage study, and elucidate the steps to do so. Furthermore, we discuss the value of including unaffected individuals into the analysis, as well as of looking at larger pedigrees, both with parametric and nonparametric methods. Our considerations and suggestions aim at guiding researchers to genotyping individuals at a trait locus as accurately as possible.     

Sex inheritance in gynodioecious species: a polygenic view

Gynodioecy is defined as the coexistence of two different sexual morphs in a population: females and hermaphrodites. This breeding system is found among many different families of angiosperms and is usually under nucleo-cytoplasmic inheritance, with maternally inherited genes causing male sterility and nuclear factors restoring male fertility. Numerous theoretical models have investigated the conditions for the stable coexistence of females and hermaphrodites. To date, all models rest on the assumption that restoration of a given male sterile genotype is controlled by a single Mendelian factor. Here, we review data bearing on the genetic determinism of sex inheritance in three gynodiecious plant species. We suggest that restoration of male fertility is probably best viewed as a quantitative trait controlled by many loci. We develop a threshold model that accommodates an underlying polygenic trait, which is resolved at the phenotypic level in discrete sexual morphs. We use this model to reanalyse data in Thymus vulgaris, Silene vulgaris and Plantago coronopus. A simple Mendelian inheritance of sex determinism is unlikely in all three species. We discuss how our model can shed additional light on the genetics of restoration and point towards future efforts in the modelling of gynodioecy.     

Cross-cultural patterns of marriage and inheritance: A phylogenetic approach

There is a strong correlation between marriage system and wealth inheritance pattern across societies (Hartung 1982); as the degree of polygyny increases, so too does the degree of male bias in inheritance. In this paper, we reevaluate this pattern using a new technique in cross-cultural analyses that effectively controls for the nonindependence of cultures (Galton's problem) through the identification of independent instances of cultural change (Mace and Pagel 1994). First, we produce cultural phylogenetic trees for the societies under study, from phylogenies previously constructed on the basis of linguistic similarity (Ruhlen 1987). Then, following standard methods for the analysis of discrete characters on phylogenetic trees, we use parsimony to determine the ancestral condition of both marriage and inheritance, and subsequently tally the number of independent instances of cultural change in each trait. The results show that transitions to polygyny are much more commonly associated with male-biased inheritance than are transitions to monogamy across human societies in our sample. They illustrate how the degree of change in the evolution of these traits differs considerably between divergent cultural groups. The advantages of this technique are discussed.     

An allelism test for quantitative trait genes

Analytical modeling has been used to test assumptions on the mode of inheritance of a quantitative trait in the course of diallel crossing between pure lines that are sufficient for adequacy of a simple regression model. This model frequently proved to be adequate in analysis of numerous data on diallel crossings of wheat and maize. An allelism test for quantitative trait genes has been suggested. Computer simulation has been used to estimate the effect of random experimental errors and deviations from the model assumptions.