Modes of selection

Modes of selection

Modes of selection Stabilizing Selection Cumulative effects of disruptive selection can be large Chose high and low oil

plants to breed Disruptive selection Selected only flies with high or low number of bristles to reproduce

Selection Does Not Mean Evolution!!! Evolution is a change in the frequencies of alleles in a population Selection can lead to evolution if the difference in reproductive success is tied to genetic variation Speed of change (evolution) depends on Amount of variation

Selection differential (S) Heritability (h2) Evolutionary response to selection Imagine a lake stocked with bluegills Evolution only results if the difference in size is due to additive genetic differences between individuals

If difference in size is due to environment (temperature or crowding competition) h2 = 0, If only the larger ones reproduce Offspring will still have same size distribution as parents No evolution Selection can be weak or strong still no evolution

Selection differential measures the strength of selection Fish example. Fig 7.9 Evolutionary response to selection If h2 = 0, then selection will result in larger fish because breeding parents were larger etc.

R = h2 x S Evolution occurs High heritability results in larger change Calculating the evolutionary response to

selection R = h2 x S Key Concepts Evolution and selection are not the same Selection can occur without evolution

The magnitude of change depends on: Strength of selection (selection differential) Heritability Quantitative trait locus (QTL)analysis links traits with genes Can use technique to map loci of interest map genome (if desired)

Mate two purebred fish parents Mate F1 x F1 to get many, many F2 fish Identify large number of short segments of DNA Single nucleotide polymorphisms SNPs Simple sequence repeats

Transposable elements QTL Analysis Markers selected so that alleles at each one are different depending on whether they are inherited from male or female chromosome Examine F2 offspring for these genetic markers and test whether the genotype at particular markers is associated

with the phenotypic trait of interest. Markers that have a statistically significant association with the expression of a phenotypic trait are called quantitative trait loci QTLs QTL analysis of coat color in mice QTL analysis of coat color in mice

Much of variation in coat color explained by differences in two genes Epistatic interaction Corin only explains a small amount of variation

Expression of Agouti during development influences coat color Expression of Agouti during development influences coat color Agouti is expressed in mouse embryo 12 days after conception

Mice are not making pigment this early, Agouti lays down a pre-pattern As embryo develops, certain cells in epithelium differentiate into pigmentproducing melanocytes and migrate into hairs, Agouti delays maturation of melanocytes. Expression strongest on ventral side of embryonic mouse, weakest on dorsal side.

So, slow-maturing melanocytes on belly fail to reach hairs and cannot color them Dorsal melanocytes turn the hairs brown Genetic manipulation of dark mice makes them lighter Engineered mainland mice to be homozygous for lite color

of Agouti. Offspring showed movement of Agouti furthur towards the dorsal side. Key Concepts QTL analysis identifies regions of the genome associated with phenotypic variation Environmental influences on quantitative

traits VP = V G + V E Total phenotypic Variance due to Variance due to variance in genetic environmental population differences

differences Phenotypic plasticity A single genotype produces different phenotypes de-pending on the environment

Reaction norm First two rows difference due to phenotypic plasticity; no genetic effects

Phenotype determined by G and E Genotype x environment interaction

Phenotypic plasticity in Caenorhabditis elegans Shows genetic basis of Phenotypic Plasticity Plasticity can evolve Mate biggest body size difference

Mate smallest body size difference Random mating Result Plasticity evolved Bigger difference Smaller difference

S. Scheiner Rapid change can lead to mismatch between plastic traits and environment Key Concepts When plasticity is heritable, the response can evolve

Recently Viewed Presentations

  • Presentación de PowerPoint

    Presentación de PowerPoint

    Además su diseño responsive permite una perfecta visualización tanto en dispositivos de mesa como en dispositivos móviles. Como nuestro objetivo es crear comunidad en Medios Sociales sugeriría revisar los íconos de Redes Sociales porque actualmente no redirigen a sus perfiles...
  • Transcription factors - introduction

    Transcription factors - introduction

    Transcription factors II ... diagnostics are becoming very widespread as genes are matched with diseases huge growth area for the future big pharma is dumping billions into diagnostics room for great benefit and widespread abuse diagnostics will enable early identification...
  • Surpluses in the hydrological cycle Today we are

    Surpluses in the hydrological cycle Today we are

    Also known as the flood recurrence interval. Estimate of the likelihood of a flood of a certain size recurring. A flood likely to happen once in ten years has a 10% chance of happening in any one year. However…. This...
  • Status Report on the 2015/17 Drought PRESENTATION TITLE

    Status Report on the 2015/17 Drought PRESENTATION TITLE

    Desiltationsystems to be installed in future e.g assessment of various sand traps options available for raw water; ... small scale desalination where water quality is not acceptable and the carting of water by tanker. The most severe drought effected towns...
  • Types of Geography: - Paulding County School District

    Types of Geography: - Paulding County School District

    Types of Geography: Population Geography Political Geography Urban Geography Economic Geography Population Geography Population Geography studies aspects of population such as birth and death rates, population distribution, and population density.
  • Writing the Report - Higher Ed eBooks &amp; Digital Learning ...

    Writing the Report - Higher Ed eBooks & Digital Learning ...

    Do you find any errors in grammar, spelling, punctuation, and word usage? Does a colleague catch any errors you may have overlooked? Have you excluded extraneous information?
  • ROMANTICISM Think-Pair-Share: What does it mean to call


    Statement 1. The answers to life's most puzzling questions can be found through discussions with a simple person who lives in the country close to nature - not with a sophisticated, well-educated person from the city.
  • The Spanish alphabet - Yola

    The Spanish alphabet - Yola

    The Spanish "d" is similar to the English "d" but is pronounced with the tongue farther forward against the upper teeth. When initial or after the letters n or l, it is harder; Daniel es mi hermano. andar ¡Buena idea!...