Mendel discovered that inheritance follows rules of chance.

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Mendel discovered that inheritance follows rules
of chance.

• Ch 10 Sec. 2

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Terms to know

• Trait
• a variation of a particular character
• Example red flowers or yellow flowers
• Genotype
• The coding on the genes that determine traits
• Example HH, Hh or hh
• Phenotype
• The physical trait that the child exhibits
• Blue eyes, skin color, hair texture, etc.
• Self-pollination
• Male and female parts pollinate the same flower
• Cross-pollination
• Male parts removed from one flower and the flower
  is then dusted with pollen from another flower

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More terms to know

• Hybrid
• The offspring of two different true-breeding
  varieties (Hh)
• Monohybrid cross
• A pairing in which the parent plants differ in
  only one character
• Purple flower crossed with a white flower
• Alleles
• Alternate forms of genes
• Flower color (Pp) 1 allele for purple, 1 allele
  for white
• Homozygous
• Two alleles are the same (HH or hh)
• Heterozygous
• Two alleles are different (Hh)
• Dominant allele
• Characteristic seen in the heterozygous or
  homozygous dominant
• Represented by Capital letter
• Recessive allele
• Characteristic does not appear unless 2 are
  together homozygous recessive
• Represented by Lowercase letter

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Principle of Segregation

• The parental plants are called the P generation
  (P for parental), and the hybrid offspring are
  the F1 generation (F for filial, from the Latin
  word for "son"). When the F1 plants
  self-fertilize or fertilize each other, their
  offspring are the F2 generation.

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How do we predict the outcomes of crosses?

• Go back to Mendels pea plants
• Purple flower crossed with a white flower
• Alleles
• Purple P white p
• Parental Generation (P generation)
• Purple PP white pp (each parent carries 2
  alleles)

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P
P
Genotypic Ratio PP Pp Pp Phenotypic
Ratio Purple White
Pp
Pp
p
p
Pp
Pp
All offspring (F1) are heterozygous for flower
color (Pp)
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• The F1 generation plants were allowed to
  self-pollinated
• Pp x Pp

Genotypic Ratio PP Pp Pp Phenotypic
Ratio Purple White
P
p
P
Pp
PP
p
F2 generation 1PP2Pp1pp 3 purple 1 white
Pp
pp
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Now you try

• Seed color
• Yellow seed color is dominant to green seed color
• Alleles
• Yellow
• Green
• Now cross a pure-breeding plant with yellow seeds
  with a pure-breeding plant with green seed (P
  generation)

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Genotypic Ratio Phenotypic Ratio
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Your F1 offspring are?

• All Yy and yellow
• Now let your F1 offspring self-pollinate

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Genotypic Ratio Phenotypic Ratio
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Your F2 offspring are?

• 1 YY 2 Yy 1 yy
• 3 yellow 1 green

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Summary of Mendel's Results

• The F1 offspring showed only one of the two
  parental traits, and always the same trait.
• Results were always the same regardless of which
  parent donated the pollen (was male).
• The trait not shown in the F1 reappeared in the
  F2 in about 25 of the offspring.
• Traits remained unchanged when passed to
  offspring they did not blend in any offspring
  but behaved as separate units.
• Reciprocal crosses showed each parent made an
  equal contribution to the offspring.

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Mendel's Conclusions

• Evidence indicated factors could be hidden or
  unexpressed, these are the recessive traits.
• The term phenotype refers to the outward
  appearance of a trait, while the term genotype is
  used for the genetic makeup of an organism.
• Male and female contributed equally to the
  offsprings genetic makeup therefore the number
  of traits was probably two (the simplest
  solution).
• Upper case letters are traditionally used to
  denote dominant traits, lower case letters for
  recessives.

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What is the genotype of an organism that displays
the dominant genotype?

• Example You have a purple flower
• Is its genotype PP or Pp?
• Use a Testcross to determine the genotype
• Breeds an individual of unknown genotype, but
  dominant phenotype with a homozygous recessive
  individual

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Figure 10-6
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Monohybrid Crosses

• Mendel looked at individual traits
• Seed Shape
• Round
• Wrinkled
• Seed Color
• Yellow
• Green

• What happens if you look at a plant for two
  traits at the same time?
• Seed shape and color
• Do the dominant alleles stay together?
• Do the recessive alleles stay together?

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Principle of Independent Assortment

• What happens when you cross organisms that differ
  in two characters DIHYBRID CROSS
• True-breeding plant with round yellow seeds
  crossed with a plant that is true-breeding
  wrinkled green seeds
• What are the parent genotypes?

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Parent genotypes

• Round wrinkled
• Yellow green
• True-breeding round yellow
• RRYY
• True-breeding wrinkled green
• rryy
• How do we determine the offspring (F1 generation)?

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How do we determine the offspring (F1
generation)?

• Use a 4 x 4 punnett square
• Determine the gametes (think FOIL from math
  class)
• RRYY
• RY RY RY RY
• rryy
• ry ry ry ry
• Set up your large punnett square

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Genotypic Ratio Phenotypic Ratio
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• F1 Generation
• Genotypic ratio
• All RrYy
• Phenotypic ratio
• All round yellow seeds
• What happens if we let those offspring
  self-pollinate?

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What happens if we let those offspring
self-pollinate?

• Determine the gametes for the punnett square
• RrYy
• RY Ry rY ry
• RrYy
• RY Ry rY ry
• Set-up your large punnett square

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Genotypic Ratio Phenotypic Ratio
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