Mendelian Genetics 1. Gregor Mendel (1822-1884) Father of genetics Austrian Monk Between 1856 –...

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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 true-breeding peas by allowing them to self-fertilize

• 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 GenerationAll tall

F1 Generation

F2

Generation3 tall, one short

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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