Fundamentals of Genetics

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Fundamentals of Genetics
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Gregor Mendel (1822-1884)

• Monk from Austria
• He bred pea plants in monastery gardens and used
  math to interpret his findings
• He is the Father of Genetics
• Even though he was never recognized in his
  lifetime!

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Mendels Garden Peas

• Mendel observed seven characteristics when using
  purebred pea plants. Each characteristic trait
  occurred in two contrasting alleles.
• Traits a distinguishing characteristic that is
  inherited such as eye color, leaf shape and tail
  length.
• Allele different forms of a trait

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Mendels Observations

• Mendel observed 7 characteristics of pea plants.
  ex - seed color (green or yellow)
• - seed texture (smooth or wrinkled)
• - flower color (purple or white)
• He used his knowledge of statistics to analyze
  his observations.
• Crossed plants (mated), collected seeds, recorded
  observations, then planted seeds, then recorded
  new plant characteristics.

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Mendels Methods

• Pollination occurs when pollen grains produced
  in the male reproductive parts of a flower
  (called anthers) are transferred to the female
  reproductive part of a flower (called stigma).
• 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.

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• Cross-pollination involves pollen transfer with
  flowers of two separate plants.
• First Mendel snipped off the anthers
• Then he dusted the stigma with pollen taken from
  the desired father.

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• Finally he tied bags over the flowers to keep out
  any stray pollen.
• ?This gave him control over the pollination of
  his pea plants (no wind or insects could
  interfere!)

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• He observed that purple-flowering plants grew
  from the seeds of purple plants, but he noticed
  that some white-flowering plants also grew from
  the seeds of purple-flowering plants.
• Mendel wanted to find an explanation for such
  variations.

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Mendels Laws

• AKA Patterns of Inheritance

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Mendel Discovered Dominance

• 1st Cross pure Tall x pure Short

Tall
All Tall
?
Short
X
Tallness Dominant Short Recessive
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• Dominance- allele expressed when present in
  genotype
• Recessive- allele expressed ONLY when two copies
  are present

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Now Breed the Hybrid

• 2nd Cross hybrid Tall x hybrid Tall. Plants
  self pollinate (self-fertilize)
• Hybrid- containing contrasting alleles

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• Tall x Tall ? ?
• Results in math
• 3/4 tall 1/4 short plant
• Recessive trait reappears!!!

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Law of Segregation

• Organisms inherit two copies of each gene/trait
  alleles.
• Alleles segregate (separate) during the formation
  of sperm and eggs.
• Organism donates ONE copy of each gene in
  fertilization.

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Alleles

• Def Allele is an alternative form of a gene (ex
  tall and short for PLANT HEIGHT)
• One allele T is for tallness
• One allele t is for shortness
• T allele is dominant over t allele.
• Tt Tall
• TT Tall
• tt short

Certain traits do not blend!! (no medium height)
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• Same Phenotype
• Different Genotype

TT
Tt
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• Homozygous when both alleles of a pair are
  alike. (Ex TT or tt)
• (can be homozygous dominant or homozygous
  recessive)
• Heterozygous when the two alleles in the pair
  are different. (ex Tt)

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Punnet Square

• A grid system to predicting all possible
  genotypes and phenotypes that result from a
  cross.
• Is a shorthand way of showing how the gametes
  behave in a cross.

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Monohybrid Cross

• a cross between one trait (ex plant height, OR
  hair texture)

t
T
Tt tt
Tt tt
t
t
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Testcross- cross between an organism with
homozygous recessive genotype and a second
organism with an unknown genotype.

• The offspring results will show whether the
  organism with unknown genotype is heterozygous or
  homozygous dominant.

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Dihybrid Cross

• a cross between two traits (ex plant height and
  seed color)
• Mendels question are traits inherited together?
• Ex Do people with Blond hair always have blue
  eyes? Do purple flowers always make smooth
  seeds?
• Do seeds that are round have to be yellow???

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2. Law of Independent Assortment

• Traits segregate (separate) independently during
  the formation of sperm and eggs.
• They then come together again in the new
  offspring (kid)