Mendels Legacy

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Mendels Legacy

• Section 9.1

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Gregor Mendel

• Gregor Mendel his knowledge of statistics later
  proved valuable in his research on heredity the
  transmission of characterizes from parent to
  offspring
• Mendel traced inheritance of individual traits
  and kept careful records of numbers.

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Mendels Garden Peas

• Observed seven characteristics of pea plants
• Occurs in two contrasting traits
• plant height (long or short stems),
• flower position along stem (axial or terminal),
• pod color (green or yellow),
• pod appearance (inflated or constricted),
• seed texture (smooth or wrinkled),
• seed color (yellow or green)
• flower color (purple or white)

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• He chose the garden pea, Pisum sativum, because
  peas were easy to cultivate, had a short
  generation time, and could be cross-pollinated.
• From many varieties, Mendel chose 22
  true-breading varieties for his experiments.
• True-breeding varieties had all offspring like
  the parents and like each other

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Mendels Methods

• Documented traits by controlling how pea plants
  were pollinated
• Pollination occurs when pollen grains produced in
  the male reproductive parts of a flower, called
  the anthers, are transferred to the female
  reproductive part of a flower called the stigma

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• Self-pollination occurs when pollen is
  transferred from the anthers of a flower to the
  stigma of either the same flower or a flower on
  the same plant (pea plants normally reproduce
  this way)
• Cross-pollination involves flowers of two
  separate plants

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• Cross-pollination occurs by removing the anthers
  from a flower and manually transferring the
  anther of a flower on one plant to the stigma of
  a flower on another plant
• Mendel was able to protect his flowers from
  receiving any other pollen that may be
  transferred from wind or insects

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Mendels Experiments

• Plants that are pure for a trait always produce
  offspring with that trait
• Strain denotes plants that are pure for a
  specific trait
• Mendel produced strains by allowing the plants to
  self-pollinate for several generations
• Obtained 14 strains, one for each of the 14
  traits he observed
• He called each strain a parental generation or P1
  generation

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• He then cross-pollinated these strains by
  transferring pollen from the anthers of a plant
  pure for one trait to the stigma of another plan
  pure for the contrasting trait
• Once plants matured, he recorded the number of
  each type of offspring produced by each P1 plant.
• Called the offspring of the P1 generation the
  first filial generation or F1 generation

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• Allowed the flowers from the F1 generation to
  self-pollinate and collected the seeds
• Mendel called the plants in this generation
  second filial generation or F2 generation

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Results and Conclusions

• Whenever he crossed strains, one of the P1 traits
  failed to appear in the F1 plants
• That trait reappeared in a ratio of 31 in the F2
  generation
• Found that F1 plants resembled only one of the
  parents
• Characteristics of the other parents reappeared
  in about ¼ of F2 plants and ¾ of offspring
  resembled the F1 plants

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Recessive and dominant traits

• Hypothesized that the trait appearing in the F1
  generation was controlled by a dominant factor
  because it masked or dominated, the other factor
  for a specific characteristic
• Trait that did not appear in the F1 generation
  but reappeared in the F2 generation was through
  to be controlled by a recessive factor

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Law of segregation

• States that a pair of factors is segregated, or
  separated, during the formation of gametes
• Each reproductive cell, or gamete, receives only
  one factor of each pair.
• When the two gametes combine during
  fertilization, the offspring then have two
  factors controlling a specific trait

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Law of independent assortment

• States that factors for different characteristics
  are distributed to gametes independently
• Crossed plants with 2 different characteristics,
  seed color and flower color

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Chromosomes and Genes

• Molecular genetics study of the structure and
  function of chromosomes and genes
• Because chromosomes occur in pairs so do genes
• Allele each of several alternative forms of a
  gene
• Mendels law of independent assortment is
  supported by the fact that chromosomes segregate
  independently to gametes during meiosis
• Law of independent assortment is observed only
  for genes located on separate chromosomes or
  located far apart on the same chromosome