Genetics

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Genetics

• Mendel And His Peas

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Genetics the scientific study of heredity

• Gregor Mendel 1800s
• His monastery garden pea plant experiments
  laid the foundations of the science of genetics.

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Summary of the pea plant experiments

• 1) Mendel developed pure-bred (true-breeding)
  plants by allowing plants to self-pollinate.
  (always produce identical offspring)

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In order to discuss whats next we must look at
the structure of a pea plant flower
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• (a) stigma traps pollen e) stamen
  anther filament
• (b) anther makes pollen (f) carpel (or
  pistil)
• 
  stigma, and style
• (c ) ovary eggs and seeds g) sepal (bud
  leaf)
• form here
• (d) filament lifts anther

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• 2) Mendel crossed-pollinated pure bred plants and
  then crossed their offspring. (anther cut off one
  plant to eliminate its pollen, and then dusted
  pollen from another plant.)

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• 3) After numerous
• experiments,
• Mendel analyzed
• data and drew
• conclusions
• about
• inheritance.

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WHAT EXACTLY DID MENDEL DO?

• First, Mendel crossed a pure-bred (true
• breeding) TALL plant with a pure-bred SHORT
  plant.
• Result The offspring were all TALL.

about 6 feet tall
under two feet
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• Second, Mendel crossed two of the TALL
  offspring.
• Result ¾ of the offspring were TALL
• ¼ of the offspring were SHORT

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• (This same result happed
• for other characteristics
• such as seed shape,
• seed color, position
• of flowers etc.
• --pg 264) Seven
• pea plant traits
• studied by Mendel

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WHY DID THIS HAPPEN?

• Mendel found that some
  genes for specific traits
  are dominant over other
  genes.
• Contrasting genes for a
  particular trait are called
  alleles, so they are dominant
  alleles.
• The genes that are not expressed because dominant
  alleles are present, are said to be recessive
  alleles.

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Using Punnett Squares to explain Mendels
results

• They were
• developed by

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• Actual pollen grains

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• Try this
• What if Mendel crossed an
  F1offspring
  pure-bred tall
• (heterozygous) with a (homozygous)
  plant.
• X
• What would be the phenotypic genotypic ratios?

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Monohybrid Dihybrid Crosses
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• The principle of dominance some alleles are
  dominant and some are recessive. Dominant allele
  blocked the expression of recessives. (Mendel
  called alleles or genes factors)

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• The principle of segregation alleles separate
  during the formation of gametes.
• The principle of independent assortment- genes
  for different traits can segregate independently
  during the formation of gametes.
• (where one allele goes does not affect where the
  other goes.)

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• He was a mathematician and
• statistician he was better
• able to analyze his data.
• He worked with large
  
• numbers of plants etc..
• He luckily chose plant traits to
• observe, in which the alleles for
• those traits were on separate
• chromosomes, or at least not
• close together.