10.1 Mendel

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10.1 Mendels Laws of Heredity

• Part 1

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Heredity

• Why do we look the way we look?

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Heredity

• We are all unique, but we have things in common
  with our family members.

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Heredity

• Characteristics that are inherited are called
  traits.
• Bent pinky
• Tongue rolling
• Detached earlobe
• Hitchhikers thumb
• Widows peak

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Heredity

• These are traits you got from your parents.
• The passing on of characteristics from parents to
  offspring is called heredity.
• Genetics is the branch of biology that
  studies heredity.

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Mendels Research

• Austrian Gregor Mendel wanted to know why
  offspring look like their parents.
• Mendel began to breed pea plants to study the
  inheritance of their traits.

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Mendels Research

• Garden pea plants reproduce sexually.
• Plants make two different sex cells, male and
  female
• Sex cells are called gametes.

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Mendels Research

• A pea plant makes both male and female gametes.
• Male pollen
• Female ovule
• located in pistil

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Mendels Research

• Pollination is the transfer of male pollen grains
  to the pistil.

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Mendels Research

• Fertilization happens when the male and female
  gametes meet and develop into a seed.

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Mendels Research

• Mendel could let a plant pollinate itself or he
  could take pollen from one and place on pistil
  of another

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Mendels Research

• Mendel studied one trait at a time
• Monohybrid crosses study breeding of plants
  that are the same except for one trait
• A hybrid is the offspring of parents that have
  different forms of a trait, tall or short height

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Mendels Research

• Mendel started with two plants, one tall and
  one short.
• He cross-pollinated them and planted the seeds
  that formed.

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Mendels Research

• The first generation of offspring were all tall.

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Mendels Research

• He let those plants self pollinate and planted
  the seeds again.
• The second generation of offspring were mostly
  tall, but there were a few short ones.
• 3 tall 1 short

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Mendels Research

• Mendel found seven different traits that showed
  the same pattern, 31 in the second offspring
  generation

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Mendels Research

• Mendel concluded that each plant has two factors
  that control each trait, one from each parent.
• He did not know what these factors were, we now
  call them alleles.
• Alleles are alternative forms of a gene that
  determine the visible trait.

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Mendels Research

• So, why did the first offspring generation (F1)
  have all tall plants?
• Why did the second offspring generation have 3
  tall 1 short plant?

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Mendels Research

• So, why did the first offspring generation (F1)
  have all tall plants?
• Mendel called the form that showed dominant
• The trait that disappeared he called recessive

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Mendels Research

• Why did the second offspring generation have 3
  tall 1 short plant?
• The plants in F1 had one allele for tall
  and one for short.
• Since tall is dominant all were tall.

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Mendels Research

• When F1 pollinated and produced seeds, some of
  the next generation (F2) had two short alleles.
• F2 generation had 3 tall plants for
  every 1 short plant