The work of Gregor Mendel

1
The work of Gregor Mendel

• Austrian monk
• Father of Genetics
• Previous views of Inheritance
• Blending
• Spermists
• Ovists

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Father of Genetics

• Mendel performed breeding experiments with garden
  peas
• Found mathematical patterns of inheritance
• His work was not appreciated until 1900, 16 years
  after his death

3
Mendels work

• Why breed peas?
• They were available in many varieties,
  inexpensive, short life cycle, simple procedures,
  easy to grow.
• The use of plants also allowed strict control
  over the mating.
• He chose to study only characters that varied in
  an either-or rather than a more-or-less
  manner.

4
Tracking heritable characteristics

• Mendel tracked heritable characters for 3
  generations.
• When F1 hybrids were allowed to self-pollinate a
  31 ratio of the 2 varieties occurred in the F2
  generation.

5
Interpreting Mendels Data
Parent Cross F1 generation F2 generation Actual Ratio Probability Ratio
Round x wrinkled 100 round 5,474 round 1,850 wrink. 2.961 31
Yellow x green pea 100 yellow 6,022 yell 2,001 green 3.011 31
Long x short stem 100 long stem 787 long 277 short 2.841 31
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Mendels Observations

• dominant vs recessive
• Before genes and meiosis was thought of,
  Mendel theorized that inheritance factors
• are in the pollen and ova of peas as alternate
  forms for different traits.
• occur in pairs, (equal contribution from both
  parents)
• separate during gamete formation and pair up
  again at fertilization

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Mendels Law of Segregation

• Each hereditary characteristic is controlled by
  two factors (alleles) that separate and pass into
  reproductive cells (gametes).

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Mendels Law of Independent Assortment

• Pairs of inheritance factors (alleles) segregate
  independently of each other when sex cells
  (gametes) are formed.

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Mendelian Inheritance in Humansdominant
recessive

• Tongue Roller (T)
• Free Earlobes (F)
• Dimples (D)
• Widows Peak (P)

• Cant roll tongue (t)
• Attached lobes (f)
• No dimples (d)
• Straight hairline (w)

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Genetics and Probability

• See handout and discuss
• Coin flipping
• Card picking
• Grab colored marbles

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Some Vital Vocab.

• Genetics
• Gene vs Chromosome
• Alleles
• Dominant vs Recessive

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Some Vital Vocab.

• Genotype vs Phenotype
• Homozygous vs Heterozygous
• Diploid vs Haploid
• Mitosis vs Meiosis
• Zygote

13
Problem Solving from Mendelian Genetics

• Consider inheritance patterns for
• Cystic fibrosis
• Huntingtons disease
• Hemophelia
• Colorblindness pedigree

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Exceptions to Complete Dominance

• Polygenic Traits
• Intermediate Expression (aka incomplete
  dominance)
• Multiple Alleles
• Several described at this link!