Mendel

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Mendels Legacy

• Section 9.1

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• Genetics- the field of biology devoted to
  understanding how characteristics are transmitted
  from parents to offspring
• Genetics was founded with the work of Gregor
  Johann Mendel

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Gregor Johann Mendel

• Austrian monk who experimented with garden peas
• 1842- age 21 entered a monastery in Brunn
• 1851- entered the University of Vienna
• Heredity- the transmission of characteristics
  from parents to offspring

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Mendels garden peas

• Mendel observed 7 characteristics of pea plants,
  each occurring in 2 contrasting traits.
• 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), flower color (purple or white)

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• Mendel collected seeds from his pea plants
• He observed that both purple-flower and
  white-flower plants grew from the seeds of
  purple-flower plants

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• He also observed that both tall and short plants
  grew from seeds obtained from tall plants
• Mendel wanted to find an explanation for the
  variations

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Mendels methods

• Mendel documented the traits of each generations
  parents by controlling how much the plants were
  pollinated
• Pollination- occurs when pollen grains produced
  in the male reproductive parts of the flower
  (anthers) are transferred to the female
  reproductive part of the flower (stigma)

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• Self-pollination- occurs when pollen is
  transferred from the anthers of a flower to
  either the stigma of the same flower or a flower
  on the same plant
• Cross-pollination- involves flowers of 2 separate
  plants

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• Self-pollination can be interrupted (and
  cross-pollination performed) by removing the
  anthers from a flower and manually transferring
  the anther to the stigma of another plant
• By doing this, Mendel was able to protect his
  flowers from receiving pollen that might be
  transferred by wind or insects, giving him more
  control over the pollination of his pea plants

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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 trait
• P1 generation- each parental generation

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• F1 generation- the first filial generation
• F2 generation- the second filial generation

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• Mendels Crosses Results
• P cross F1 generation F2
  generation Actual ratio Probability ratio
• Axial X Terminal Axial 651
  axial 3.141 31
• 
  207 terminal
• Tall X Short tall
  787 tall 2.841 31
• 
  277 short
• Inflated X inflated 882
  inflated 2.951 31
• Constricted
  299 cons.
• Green X yellow green 428
  green 2.821 31
• (pods)
  152 yellow
• Smooth X smooth
  5,474 sm. 2.961 31
  
• Wrinkled
  1,850 wrink.
• Yellow X Green yellow 6,022
  yellow 3.011 31
• (seeds)
  2,001 green
• Purple X White purple 705
  purple 3.151 31
• 
  224 white

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Recessive Dominant traits

• Dominant factor- dominates the other factor of a
  specific characteristic
• Recessive factor- the trait that did not appear
  in the F1 generation but reappeared in the F2
  generation

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Law of segregation

• States that a pair of factors is segregated, or
  separated, during the formation of gametes.

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Law of independent assortment

• States that factors for different characteristics
  are distributed to gametes independently.

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Chromosomes Genes

• Molecular genetics- the study of the structure
  and function of chromosomes and genes
• Allele- each of several alternatives of a gene
  (Mendel's factors are now called alleles.)