11-3 Exploring Mendelian Genetics

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11-3 Exploring Mendelian Genetics

• Key Concepts
• What is the principle of independent assortment?
• What inheritance patterns exist aside from simple
  dominance?
• Vocabulary
• Independent assortment
• Incomplete dominance
• Codominance
• Multiple alleles
• Polygenic traits

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Two-Factor (Two-Gene) Cross

• Why is this called a two factor cross?
• Because the experiment tests two
  characteristics
• controlled by two genes.
• Mendels Experiment Two-factor cross
• Mendel crossed two homozygous plants (Pgen)
• He looked at two genes (seed shape and seed
  color)
• Pgeneration Round Yellow x Wrinkled Green
• F1 offspring produced?
• F1 generation All Round Yellow peas
• Which alleles are dominant?
• Round shape and Yellow color.

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Summarization Mendels two factor cross

• Mendel crossed plants that were homozygous
  dominant for round yellow peas (RRYY) and plants
  that were homozygous recessive for wrinkled green
  peas (rryy).
• All of the F1 offspring were heterozygous
  dominant for round yellow peas (RrYy).

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In a monohybrid cross . . .

• If the genotype of a plant is Tt, each parent can
  only pass on one allele per gene in their
  gametes. (gene height)
• Tt
• T or t

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For a dihybrid cross . . .

• If the genotype of a plant is TtYy, each
  parent can STILL only pass on one allele for each
  gene in their gametes.(gene height and leaf
  shape)
• TtYy
• TY or tY or Ty or ty

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Principle of Independent Assortment

• States that genes for different traits can
  segregate independently during the formation of
  gametes (meiosis).
• If the genotype of a plant is TtYy (T gene for
  height Y gene for leaf shape), what are the
  four possible combinations of gametes?
• how do you figure out the gametes?

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How do you figure out the possible gametes?

• Remember FOIL (from math???
• the distributive property)
• T t Y y
• The gametes mom will produce

F First O Outside I Inside L Last
Ex Moms genotype
TY, Ty, tY, ty
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Independent Assortment..in other words

• Does the segregation of one pair of alleles
  affect the segregation of another pair of
  alleles?
• EX does the gene that determines seed shape have
  anything to do with the gene that determines seed
  color?
• The answer NO
• If genes are not connected, then they should
  separate (segregate) independently Independent
  Assortment

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P generation
F1 generation

• If you wanted to cross the offspring of the F1
  generation
• What would the gametes be? (use FOIL)
• SsYy SY, sY, Sy, sy
• SsYy SY, sY, Sy, sy
• NEXTtry the cross to get the F2 generation!!!

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SsYy x SsYy

• SY Sy sY
  sy
• SY
• Sy
• sY
• sy

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SsYy x SsYy

• SY Sy sY
  sy
• SY
• Sy
• sY
• sy

SSYY SSYy SsYY SsYy
SSYy SSyy SsYy Ssyy
SsYY SsYy ssYY ssYy
SsYy Ssyy ssYy ssyy
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Independent Assortment

• The alleles for seed shape segregated
  independently of the alleles for seed color.
• This phenomenon is known as
• Independent assortment (the 2 genes are on
  different chromosomes.)