Evolutionary change

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Evolutionary change

• strategies
• genetic conflicts
• imprinting
• epigenetics

Whats new
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evolution
Genetic variation
Selection
environment
development
Phenotypic variation
environment
Fitness variation
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Evolution
To study the evolution of a sharks body it is
sufficient to look at the environment (prey,
properties of sea water etc.)
To study the evolution of mating behaviour we
have to consider the set of strategies played by
all members of the population.
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Evolution
Evolutionary Stable Strategy a strategy that
cannot be beaten by any mutant playing a
different strategy
Analogy Nash Equilibrium in economics (beautiful
mind)
PC Hooft Tractor
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Strategies S/R ratio
What will happen if we take away the division?
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Strategies S/R ratio

• Prediction when plants compete for nutrients
  they should increase their root to shoot ratio
  even if the total amount of nutrients available
  per plant is the same as in a situation without
  competition.

• Result without the separation total seed
  production is 30 lower

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Strategies Sex ratios

• In humans we have a simple XX XY sex
  determination system

Genotype Phenotype XX x XY f x m XX XY XX
XY f m f m
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Strategies sex ratios

• In humans sex ratio seems fixed
• In many animals and plants the sex ratio can be
  highly variable in stinging nettles it varies
  among mothers from producing almost only sons to
  almost only daughters

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Strategies sex ratios

• A line of descendents that produces only females
  multiplies at a faster rate than a line with both
  males and females

f f x m f f f x m f f f f f x m

• Questions why are so many males produced?

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Strategies sex ratios
Answer if all mothers produce daughters a mother
that produces sons would have a strong advantage
because her sons fertilize all the females in the
population and thus passes on much more genes to
the next generation In a well mixed population
with random mating the evolutionary stable sex
ratio is 50 sons
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Genetic conflict

• Cytoplasmatic genes are only passed on through
  the mother plant and have a selective advantage
  if only females are produced
• A genetic element in the cytoplasm that shifts
  the sex ratio towards more daughters will sweep
  through the population
• If its frequency has increased and there are a
  lot of females in the population there is a
  selective advantage for a nuclear gene to restore
  the effect of the cytoplasmatic gene.

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Genetic conflict
Cytoplasm

• Evolutionary theory predicts a complicated system
  of nuclear and cytoplasmatic genes with opposing
  effects
• the sex determination system will depend on the
  history of the population and will differ among
  populations of the same species
• example Plantago lanceolata, drosophila

Feminising elements
restorer genes
nucleus
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Genetic conflict Seed size

• The optimal investment of a mother in each of her
  offspring is a compromise between quality and
  offspring number
• An individual offspring mostly benefits from a
  very large investment

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Genetic conflict seed size

• Prediction among the genes of the mother there
  is a conflict between genes that give the mother
  control over offspring size and genes transmitted
  to the offspring that give the offspring control
  over their size

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Genetic conflict seed size

• However, if you take more resources yourself,
  this is at the expense of the other offspring to
  whom you are genetically related
• The latter reduces the rate at which your genes
  are transmitted to the next generation. It
  reduces your inclusive fitness.
• The degree of relatedness with the other
  offspring matters.

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Genetic conflict seed size
Seed mass Selfing species 0.036 partly selfing
species 0,590 outcrossing species 0,620
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Genomic imprinting

• Generally, genes transmitted through the father
  are less related than genes transmitted through
  the mother because multiple fathers may have
  sired the offspring of a single mother
• Prediction a gene in the embryo that leads to
  excess resources should be on when it comes
  from the father and off when it comes from the
  mother.

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Genomic imprinting

• Genes are differently expressed when they come
  from the mother or the father

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Genomic imprinting
Crossing between tetraploid and diploid
Arabidopsis thaliana
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Epigenetics
The study of heritable changes in gene function
that occur without a change in the sequence of
nuclear DNA. This includes the study of how
environmental factors affecting a parent can
result in changes in the way genes are expressed
in the offspring
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Epigenetics
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Epigenetics
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Epigenetics
Changes to the structure of the chromatin have a
profound influence on gene expression if the
chromatin is condensed, the factors involved in
gene expression cannot get to the DNA, and the
genes will be switched off. Conversely, if the
chromatin is open, the genes can be switched on
if required. DNA methylation is a chemical
modification of the DNA molecule itself it is
carried out by an enzyme called DNA
methyltransferase. Methylation can directly
switch off gene expression by preventing
transcription factors binding to promoters.
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Epigenetics