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Genetic diversity is the backbone of evolution

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Man became most important ecological factor 50000 years ago ... To boost breeding value when breeding population is creamed for production population, ... – PowerPoint PPT presentation

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Title: Genetic diversity is the backbone of evolution


1
Genetic diversity is the backbone of evolution !
2
Why do we need diversity?The large picture
  • Political demand for diversity
  • Mans activities may lead to extinction of
    populations and species
  • Mans influence seems to grow
  • Man became most important ecological factor
    ?50000 years ago
  • Diversity is the basis for evolution and thus life

3
Man destroys biodiversity
Not long ago, giant wingless birds like this moa
paced New Zealand's open country and brushy
woodlands. Without large native predators to
threaten them, moas evolved to be the biggest
land predators on their island home.
But moas couldn't stand up to human
hunting Humans first reached New Zealand by canoe
about 1000 years ago. These settlers quickly
learned to hunt the defenceless moas. In fact,
they learned too well--in only about 700 years,
every last moa was gone.
4
Biodiversity is appealing
5
Evolution
  • Diversity lost by selection and chance
  • Diversity created by mutation
  • Balance, population size 500 probably enough for
    sustainable diversity
  • Forests much larger than that
  • Forest tree breeding often operates with numbers
    larger than that (gt500)

6
Numeric example
  • The more A, the better'
  • Ranking for A
  • AAAAAA 6A
  • AAAA 4A
  • AAAA 4A
  • AA 2A
  • AA 2A
  • AA 2A
  • AA 2A
  • A 1A
  • The three top ranking has together only 8 A
  • If all are selected the potential for 10 A
    remains
  • Selecting best may mean missing something!

7
Variance in sample
A sample need not be large to preserve the
variance of the original population!
8
Rare alleles
  • What alleles are rare?
  • Almost all rare alleles are rather recent
    mutations and of no value
  • Little recent advantage
  • Most rare alleles in our forest trees will die
    away naturally.
  • Even if they are of potential value, it is not
    easy to utilise rare alleles
  • many generations to get effect
  • in few initial genomes ? inbreeding problems if
    utilised,
  • expensive screening to identify.

9
  • Mechanisms for important rare alleles
  • balanced polymorphism?
  • sometimes a little bad, sometimes very good?
  • better if in low frequency.

A gene with a frequency of 10 is likely to be
conserved but a gene with frequency of 2 is
likely to be lost in a random mating population
of size 20.
10
Limited impact of breeding
  • Areas never regenerated on purpose,
  • Natural regeneration 25,
  • Natural volunteers in plantations,
  • Pollen contamination (50 of pollen) in seed
    orchards.

11
Unimproved
12
Improved
13
Diversity in a stand
  • Genetic diversity in a stand is likely to favour
    biological production
  • A single genotype demands the same things at the
    same time, bad site use!
  • In a mix another genotype may take over the
    ecological space left by a failed genotype.
  • A disease spreads faster in a uniform crop.
  • This expectation has generally been confirmed by
    a number of experiments with different
    agricultural crops

 
14
Too much diversity in plantations?!
  • Most crop- and many forest managers do not like
    diversity,
  • Uniform trees better economy, simpler
    management - even if biological production is
    lost,
  • Genetic superiority of the best clones is much
    larger than the loss in biomass production by
    uniformity,
  • The current demand for diversity in intensively
    managed forests is in my opinion - unreasonable
    expensive in lost future gain,
  • Most of the benefits with diversity is obtained
    by five genotypes instead of an infinite number.

15
Seed orchard crops are diverse!
  • Phenotypic selection of plus trees are uncertain,
    preserves diversity,
  • Marker gene measurements indicate that seed
    orchard crops can be more diverse than stand
    seeds!
  • Seed orchard clones are recruited from a large
    area, which favours diversity compared to stands,
  • Pollen sources outside the seed orchard favours
    diversity,
  • Variances depends little on clonal number,
  • In a small piece of a natural forest, trees are
    as related as trees from a seed orchard
    plantation.

16
Measured with marker genes, most of the diversity
is within stands and little between stands, table
from (El-Kassaby 1991).   GST gives the share of
the genetic diversity that falls between stands.
17
Reasons to consider gene diversity in breeding
  • To boost breeding value when breeding population
    is creamed for production population,
  • To obtain a production population with little
    inbreeding,
  • To offer desirable gene diversity for production
    population (acceptability and production),
  • To allow more aggressive breeding in the first
    cycles,
  • To consume while accumulating additive effects,
  • To keep inbreeding manageable in the breeding
    stock,
  • To be prepared for changed emphasises,
  • To combine breeding and gene conservation,
  • Some intuitive feeling that diversity could be
    good to have,
  • To demonstrate that breeders care for
    sustainability, breeding is not mining,
  • A sense of respect,
  • Genetic diversity is the basis for the
    professions forest geneticist and tree breeder.

18
Too much diversity in breeding population?!
  • Expensive
  • In conflict with gain

19
Extremest value increases slowly with number
The most extreme value of a population is raising
extremely slow as a function of population size,
thus to increase numbers is rather unefficient!
20
Artificial selection is not a major short time
threat to diversity
  • Low heritability conserved variance also after
    intensive phenotypic selection (gets worse when
    selection is on genotype instead of phenotype),
  • 35000 genes interact to produce a phenotype. The
    influence of selection on the frequency of each
    gene must be small ,
  • Selection for quantitative traits are likely to
    be selection for different genes at different
    selection occasions.

21
Need of genetic diversity measure
  • Demonstration that we care,
  • For chiefs and "politicians" to demonstrate that
    they care,
  • To monitor operations,
  • To control operations,
  • Review and compare different options for
    operations,
  • Classify old and new forests, multiplication
    units, programs, development by time, diversity
    on stand, landscape, region and national level,
  • Trade off with other quantifiable variables in
    the breeding system, like genetic gain, cost and
    time,
  • Use for gene conservation purposes.

22
Coancestry
Coancestry is the probability that genes taken at
random from each of a pair of individuals origin
from the same gene in a common ancestor.
Group coancestry is the probability that two
genes taken at random from a population origin
from the same gene in a common ancestor
(genomsnittligt släktskap)
23
Group coancestry
  • Average coancestry including self-coancestry
    (genomsnittligt släktskap)
  • Loss of gene diversity group coancestry
  • Group coancestry is a measure of gene diversity!

24
Group coancestry and status number are useful as
diversity measures!
We need measures to control accumulation of
relatedness
25
Interaction conservation and breeding
Gene conservation can be said to keep group
coancestry low Breeding should combine a high
gain and a reasonable group coancestry or Breeding
is much the art of balancing gain and group
coancestry
26
Diversity changes at generation shifts because
  • Drift (unavoidable),
  • Balance of founder genes (can be optimised).
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