Types of Variation

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• Types of Variation
• Mendelian
• Centers of Origin/Domestication (Vavilov)
• Epicenter (greatest diversity)
• As one moves away from epicenter diversity
  decreases and specialization increases
  (speciation)
• Examples
• Soybean native to China (Domesticated lt 2800
  BC)
• Varieties (land race or cultigens) selected by
  time of Christ
• Varieties selected for medicinal purposes, food,
  and feed

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• Types of Variation
• Mendelian
• Examples
• Soybean
• Grain Sorghum
• Evolved/domesticated in NE Africa
• Transported by man across Africa where new
  species/races selected in West and Southern
  Africa
• Corn
• Evolved and selected in Mexico/C. America
• By the time of Columbus, Ameridians had selected
  types specialized for roasting, popping, and
  boiling, Today gt250 naturally occurring races in
  S. America

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• Types of Variation
• Centers of Origin/Domestication (area of greatest
  diversity)
• Chinese Center Soybean Cucumber, Pear, Sugarcane
• Indian center
• a. Main Rice, Cucumber, OW Cotton, Hemp
• b. Indo Malayan Banana, Cocoanut Palm, Black
  Pepper
• Central Asiatic Wheat, Flax, Upland Cotton,
  Onion, Apple
• Near Eastern Wheat, Barley, Alfalfa, Fig, Cherry
• Mediterranean Wheat, Clovers, Cabbage,
  Peppermint
• Abyssinian Wheat, Grain Sorghum, Okra
• South Mexican/Central Am. Maize, Lima Bean, NW
  Cotton
• South American Potato, Tomato, Pima Cotton

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• Types of Variation
• Mendelian variation that exist naturally
• Interspecific hybrids (Genus species1 x Genus
  species2)
• Development of sterile or veg. reproducable
  (incld. Apomixis) hybrids. Opportunity to develop
  huge amount of heterosis and never loose it.
  Examples of interspecific hybrids includes
  cultivars of pears, cherries, grapes, roses, and
  others.
• Modern strawberry resulted from the chance
  hybridization of Fragaria virginiana/F.
  chiloensis.
• virginiana N.A. east coast chiloensis
  N.A. west coast
• A Frenchman took collected plants of
  chiloensis to France from Chile where it was
  planted and it accidently outcrossed to
  virginiana producing the modern strawberry

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• Types of Variation
• Mendelian variation that exist naturally
• Interspecific hybrids (Genus species1 x Genus
  species2)
• a. Development of sterile or veg. reproducable
  (incld. Apomixis) hybrids.
• b. Introgression
• species 1 has resistance to some disease
• species 2 is cultivated
• Sp.1/Sp.2 gtgtF1 interspecific hybrid and in
  some cases these are fertile and we backcross
  to the cultivated type and select for the
  resistance from the donor species OR we
  introgress the trait.

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• Types of Variation
• Mendelian variation that exist naturally
• Interspecific hybrids (Genus species1 x Genus
  species2)
• Polyploidy
• a. Auto an organism with more than 2 sets of
  chromosomes derived from the same species
  (i.e. itself)
• Probably results from a failure of meiosis
  resulting in unreduced egg and/or pollen
  gametes (i.e. gametes2n)
• 2n n 3n and sterile triploid
• 2n 2n tetraploid and maybe fertile
• Autopolyploids have not been very important in
  nature because there are problems usually with
  aberrant chromosome behavior and therefore a high
  degree of sterility (if vegno problem)

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Types of Variation Pondering points about of
autopolyploids a. tend to have greater veg.
growth (thus best for crops grown for their
vegetative parts b. most successful
autoployploids come from diploids with low
chromosome numbers c. those from x-pollinated
crops may be more successful bec. x-pollination
fosters extensive gene recombination d. suggested
that optimum autoploidy levels
exist corn diploid max vigor/////tetraploids
ame phenotype but inferior agronomically banan
a diploid hard seed//////triploidseedless bl
ackberry 2x 12x no difference
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Uses of autoploidy To find superior
autotetraploid Convert a large number of
diploid genotypes and then start a crossing and
selection program (i.e. dont take a superior
diploid and expect it to be a superior
tetraploid) ex. Sugar beets cms diploid x
autotetraploid gt triploid that is sterile but
the root is the economic product Bridging or
introgression to move traits in wild diploids
into cultivated tetraploid, ex.
Cotton artificial tetraploid x G. hirsutum
Colchicine or other spindle poison
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• Types of Variation
• Mendelian variation that exist naturally
• Interspecific hybrids (Genus species1 x Genus
  species2)
• Polyploidy a. Auto
• b. Allo an organism with more than 2 sets of
  somatic chromosomes derived from the different
  species
• Probably results from a failure of meiosis
  resulting in unreduced egg and/or pollen
  gametes (i.e. gametes2n)
• ex. wheat
• T. monococcum (AA)/T. tauschii (DD)/unknown
  (BB)
• ex NW cotton G. herbaceum (AA)/G. raimondii
  (DD)

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Uses of Alleloploids More common that
autoploids Used to identify ancestoral parents
(interspecific fertility indicates genomic
relationship and allows breeders/geneticists to
determine if wild relatives can be useful in
breeding programs Used to produce new genotypes
and maybe species. Consider Triticale or
Triticosecale Secale cereal 14 Chr RR
rye Triticum turgidue 28 Chr AABB
durum wheat T. aestivum 42 Chr
AABBDD common wheat Triticosecale 42
Chr AABBRR triticale Triticosecale
56 Chr AABBDDRR triticale First recorded
successful wheat/rye cross in 1888 (Germany)
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Uses of Alloploids (contd) Facilitate the
transfer of genes from related species ex.
Genes for fiber strength in cotton G. thurberi
(D1D1) / G. arboreum (A2A2)
Colchicine
A2A2D1D1 / G. hirsutum (AADD)1 Fertile
Offspring selected higher fiber
strength Note that you could not make G. sturtian
/ G aboreum // hirsutum Because it would be
CC/AA//(AADD)1 (no pairing of C D)
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Types of Variation Aneuploidy, e.g. Chromosome
addition lines Chromosome deletion lines
primary trisomic2n 1A monosomic2n-1A
double trisomic2n 1A 1B
nullisomic2n-2A secondary
trisomic2nisochromosome A A or B represents
a complete chromosome a chromosome with
identical chromosome arms Uses 1. locating genes
to chromosomes 2. linkage studies 3.
chromosome substitution lines (i.e. insertion of
entire extra chromosome. A lot of their uses
have been circumvented by molecular genetics.
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• Types of Variation
• Haploidy haploid plants contain the haploid
  number of chromosomes in their somatic cells.
  Obviously they will be sterile. However, they
  have some use
• Prod. Of a completely homozygous diploid or pure
  line
• Mutation studies (mutations are immediately
  observable because they are not masked by the
  other allele)
• Genetic studies
• In self-incompatible spp. They can be used to
  produce inbred lines
• Deriving haploids they do occur naturally (1 in
  10,000 in corn) arising from an unfertilized egg
  developing into an embryo similar to apomixis.
  They also can be developed by anther culture in
  some species.

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• Sources of Variation (where does the breeder go
  for variation?)
• Curent cultivars
• Curent inbred lines from public programs
• Germplasm from public programs
• Colleagues
• Obsolete cultivars/germplasm lines/inbred lines
• Material from location where variability is the
  greatest.
• cold tolerant cotton northern fringes of the
  temperate zone
• boll weevil resistance center of origin
• turkey wheat 1874-1890 the desirability of
  turkey wheat for making bread spurred numerous
  collection trips
• DO YOU HAVE TO PERSONALLY GO?????