Transcript Mendelian Genetics - Edmonds School District

Mendelian Genetics
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Gregor Mendel
(1822-1884)
• Father of genetics
• Austrian Monk
• Between 1856 – 1863 he
studied ~28,000 pea
plants
• Importance of his work
not realized until 20th
century, ~20 years after
death
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Mendel’s Experiments
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The Peas
• Advantages of Pea
Plants:
– Grown in small areas
– distinct heritable
features
– Each feature has two
variants
– Lots of offspring
– Can self-fertilize or
cross fertilize
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Reproduction in Flowering Plants
• Pollen (produced by
stamen) contain sperm
• Ovary contains egg
• Pollen grows tube down
style to carry sperm to
egg
• Self-fertilization - sperm
and egg from same
flower
• Cross-fertilization - sperm
and egg from different
flower
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His Experiments
• First created truebreeding peas by
allowing them to selffertilize
• True breeding = only
produces offspring with
one specific trait
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His Experiments
• Then, he cross-fertilize
(hybridized) two
contrasting,
true-breeding varieties
(P1 generation - parent)
• Offspring is the F1
Generation – first filial
• Then allowed the F1
hybrids
to self-pollinate to produce
an F2 generation – 2nd filial
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His Experiments
P1
Generation
F1
Generation
All tall
F1
Generation
F2
Generation
3 tall, one
short 8
His Experiments
• Results:
• F1 generation: all dominant phenotypes
• F2 generation: 3:1 ratio of dominant to recessive phenotypes
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His Experiments
• Created three Laws of Inheritance
– Law of Dominance
– Law of Segregation
– Law of Independent Assortment
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Mendel’s Laws of Inheritance
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Law of Dominance
• In a cross of true-breeding parents, only one form
of the trait will appear in the next generation
• The apparent trait is dominant, the other is
recessive
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Law of Segregation
• The pair of factors (alleles) is segregated, or
separated, during formation of gametes (sperm and
egg)
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Law of Independent Assortment
• Factors (alleles) for different traits are distributed in
gametes independently of each other
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Applying Mendel’s Laws – Punnet
Squares
• Two types – used to show
expected genotype of offspring
• Monohybrid
– 2 gametes from each parent
– 2x2 grid
• Dihybrid
– 4 gametes from each parents
– 4x4 grid
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Applying Mendel’s Laws – Test Cross
• A mating between an organism with unknown
genotype and a homozygous recessive
organism
• Example:
– Mice can either be brown (B) or white (b). You
have a mouse with a brown coat.
– Can be BB or Bb
– If Bb: offspring half
brown/half white
– If BB: offspring all
brown
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