Search PubMed⌕ Search

Biomedical subjects

M Kirkpatrick

Publications and source records attributed to M Kirkpatrick.

At least 37 records · Page 2Linked to original sources
PubMed1990

Selection response in traits with maternal inheritance.

Maternal inheritance is the non-Mendelian transmission of traits from mothers to their offspring. Despite its presence in virtually all organisms, acting through a variety of mechanisms, the evolutionary consequences of maternal inheritance are not well understood. Here we review and extend a model of the inheritance and evolution of multiple quantitative characters with complex pathways of maternal effects. Extensions of the earlier model include common family environmental effects not associated with maternal phenotype, sexual dimorphism, and paternal effects (non-Mendelian influence of the father on offspring traits). We find that, in contrast to simple Mendelian inheritance, maternal inheritance produces qualitatively different evolutionary dynamics for two reasons: (1) the response to selection on a set of characters depends not only on their additive genetic variances and covariances, but also on maternal characters that influence them, and (2) time lags in the response to selection create a form of evolutionary momentum. These results have important implications for evolution in natural populations and practical applications in the economic improvement of domesticated species. We derive selection indices that maximize either the economic improvement in a single generation of artificial selection or the asymptotic rate of improvement in long-term selection programmes, based on individual merit or a combination of individual and family merit. Numerical examples show that accounting for maternal inheritance can lead to considerable increases in the efficiency of artificial selection.

Animals↗
PubMed1990

Analysis of the inheritance, selection and evolution of growth trajectories.

We present methods for estimating the parameters of inheritance and selection that appear in a quantitative genetic model for the evolution growth trajectories and other "infinite-dimensional" traits that we recently introduced. Two methods for estimating the additive genetic covariance function are developed, a "full" model that fully fits the data and a "reduced" model that generates a smoothed estimate consistent with the sampling errors in the data. By decomposing the covariance function into its eigenvalues and eigenfunctions, it is possible to identify potential evolutionary changes in the population's mean growth trajectory for which there is (and those for which there is not) genetic variation. Algorithms for estimating these quantities, their confidence intervals, and for testing hypotheses about them are developed. These techniques are illustrated by an analysis of early growth in mice. Compatible methods for estimating the selection gradient function acting on growth trajectories in natural or domesticated populations are presented. We show how the estimates for the additive genetic covariance function and the selection gradient function can be used to predict the evolutionary change in a population's mean growth trajectory.

Animals↗
PubMed1989

Genetic segregation and the maintenance of sexual reproduction.

Sexual reproduction confronts evolutionary biology with a paradox: other things being equal, an asexual (all-female) population will have twice the reproductive potential of a competing sexual population and therefore should rapidly drive the sexual population to extinction. Thus, the persistence of sexual reproduction in most life forms implies a compensatory advantage to sexual reproduction. Work on this problem has emphasized the evolutionary advantages produced by the genetic recombination that accompanies sexual reproduction. Here we show that genetic segregation produces an advantage to sexual reproduction even in the absence of an advantage from recombination. Segregation in a diploid sexual population allows selection to carry a single advantageous mutation to a homozygous state, whereas two separate mutations are required in a parthenogenetic population. The complete fixation of advantageous mutations is thus delayed in a heterozygous state in asexual populations. Calculation of the selective load incurred suggests that it may offset the intrinsic twofold reproductive advantage of asexual reproduction and maintain sexual reproduction in diploid populations.

Animals↗
PubMed1989

A quantitative genetic model for growth, shape, reaction norms, and other infinite-dimensional characters.

Infinite-dimensional characters are those in which the phenotype of an individual is described by a function, rather than by a finite set of measurements. Examples include growth trajectories, morphological shapes, and norms of reaction. Methods are presented here that allow individual phenotypes, population means, and patterns of variance and covariance to be quantified for infinite-dimensional characters. A quantitative-genetic model is developed, and the recursion equation for the evolution of the population mean phenotype of an infinite-dimensional character is derived. The infinite-dimensional method offers three advantages over conventional finite-dimensional methods when applied to this kind of trait: (1) it describes the trait at all points rather than at a finite number of landmarks, (2) it eliminates errors in predicting the evolutionary response to selection made by conventional methods because they neglect the effects of selection on some parts of the trait, and (3) it estimates parameters of interest more efficiently.

Analysis of Variance↗
PubMed1989

Symptoms and signs of progressive hydrocephalus.

The clinical features of 107 cases of children with hydrocephalus and measured raised intraventricular pressure were analysed retrospectively. Fifty one children had recently been diagnosed as having hydrocephalus, and the remainder had had shunts injected to direct the cerebrospinal fluid. The most common symptoms in the group were vomiting, behavioural changes, drowsiness, and headaches. The most common clinical signs were inappropriately increasing occipitofrontal head circumferences, tense anterior fontanelles, splayed sutures, and distension of the scalp veins. Half the infantile cases of hydrocephalus were without symptoms, and a quarter of the cases with cerebrospinal fluid shunts and measured raised intraventricular pressure were without signs. There were no fewer than 33 different clinical signs including several unusual ones, such as macular rash and sweating. We believe that the presentation of hydrocephalus with raised intraventricular pressure is sufficiently variable, unusual, or even absent to justify the direct measurement of intracranial pressure.

Cerebrospinal Fluid Shunts↗
PubMed1989

The evolution of growth trajectories and other complex quantitative characters.

Growth trajectories differ from many other quantitative characters in that they are characterized by a continuous function rather than by a finite number of discrete measurements. We review here recently developed methods for predicting the evolution of growth trajectories under the influence of natural or artificial selection. Using our method, analysis of genetic data from mice shows that the patterns of genetic variation arising from developmental processes impose constraints on evolution of growth trajectories. These constraints can be quantified to reveal the families of growth trajectories that can be produced by selection and those families that cannot. The data suggest there may be relatively few evolutionary degrees of freedom for growth trajectories despite the presence of abundant additive genetic variation to alter size and (or) growth rate at every age. The description of these constraints may be useful to both biologists who would like to determine the evolutionary options available to natural populations and to breeders who would like to alter growth trajectories to economically improve domesticated species. Our methods and conclusions can be generalized to other kinds of "infinite-dimensional" or complex characters, including morphological shapes and norms of reaction.

Age Factors↗
PubMed1988

Ecological speciation by sexual selection.

Quantitative genetic models are used to investigate a mechanism of speciation involving natural and sexual selection on a population with more than one ecological niche available. Female choice of mates, based on ecologically important characters, can initiate a sudden shift into a new niche. Whether males alone or both sexes make the transition depends strongly on the genetic correlation between homologous male and female characters. This mode of speciation rapidly produces premating and postmating isolating barriers, as well as ecological separation, between populations that can then coexist in the same area as distinct species.

Ecology↗
PubMed1988

Directional selection and the evolution of breeding date in birds.

In many bird species, those pairs that breed earlier in the season have higher reproductive success than those that breed later. Since breeding date is known to be heritable, it is unclear why it does not evolve to an earlier time. Under assumptions outlined by Fisher, a model is developed that shows how breeding date may have considerable additive genetic variance, appear to be under directional selection, and yet not evolve. These results provide a general explanation for a persistent correlation of fitness with a variety of traits in natural populations.

Animals↗
PubMed1987

Clinical implications of lesbian mother studies.

Recent surveys of lesbians have revealed that one-third have been heterosexually married, and one-half of these have had children. Studies comparing lesbian mothers and their children with divorced heterosexual mothers and their children provide data of value to clinicians preparing to evaluate or treat members of this population. Studies show similarities between the two groups in marital history, pregnancy history, child-rearing attitudes, and lifestyle. Motherhood, not sexual orientation, is the most salient factor in both group's identity. Lesbian mothers had more congenial relations with ex-spouses and included men more regularly in their children's lives. Coupled lesbians had greater economic and emotional resources and provided children with a richer family life than did mothers of either group living alone with children. No difference in frequency not type of psychological problem was found in the children. Children benefited from group discussions to relieve anxiety about changes in their lives and in their mothers' sexual orientation.

Adult↗