Fundamentals of Genetics

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Fundamentals of Genetics

• Chapter 9

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Gregor Mendel

• Genetics field of biology devoted to
  understanding how characteristics are transmitted
  from parents to offspring.
• Mendel conducted research on heredity the
  transmission of characteristics from parents to
  offspring.
• Gregor Mendel is known as the father of genetics.
  
• Experimented with garden peas.

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Gregor Mendel
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Mendels Garden Peas

• Observed seven characteristics.
• Each characteristic occurred in 2 traits.
• Height (tall/short), flower position
  (axial/terminal), pod color (green/yellow), pod
  appearance (inflated/constricted), seed texture
  (smooth/wrinkled), seed color (green/yellow) and
  flower color(purple/white).

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Mendels Methods

• Collected seeds from pea plants
• Carefully recorded characteristics of parent
  plant.
• Planted the seeds the next year.
• Noticed that purple flowering plants grew from
  purple plants, some white flowers also grew from
  purple plants.
• Noticed something similar to this with almost all
  the traits.
• He wanted an explanation for this.

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Plant Anatomy
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Mendels Experiments

• Began by growing plants that were pure for each
  trait.
• Pure plant always produces offspring with that
  trait.
• Strain denotes plants that are pure for that
  specific trait. (true-breeding)
• Mendel called each strain a parental generation
  or P1 generation.

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Mendels Experiments Cont.

• Cross pollinated strains by transferring pollen
  from a plant that was pure for trait to a plant
  that was pure for the contrasting trait.
• When plants matured he recorded the number of
  each type of offspring produced by each P1 plant.
  
• Called offspring of the P1 generation the first
  filial generation or F1 generation.
• Then allowed F1 plants to self pollinate and
  collected the seeds.
• Let the plants grow.
• Called these plants the second filial generation
  or F2 generation. (Table 9-1)

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Cross Pollination
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Mendels Results and Conclusions

• Crossed a pure tall plant with a pure short
  plant. (P1 generation).
• The F1 generation resulted in all tall plants.
• What happened to short trait??
• Allowed F1 generation to self pollinate.
• F2 generation were ¾ tall plants and ¼ short
  plants.
• Short trait returned.

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Results and Conclusions Cont.
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Recessive and Dominant Traits

• When the tall and short plant were crossed, the
  short trait of one of the P1 plants did not
  appear in the F1 plants.
• Then short trait reappeared in ¼ of F2 plants.
• Mendel hypothesized that the trait that appeared
  in the F1 generation was controlled by a dominant
  factor.
• It masked or dominated the other trait.

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Dominant and Recessive Cont.

• The trait that reappeared in the F2 generation
  was thought to be controlled by a recessive
  factor.
• Had no observable effect on an organisms
  appearance when paired with a dominant factor.
• Overpowered by the dominant trait.

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Law of Segregation

• Paired factors separate during the formation of
  reproductive cells.
• Means that each gamete receives only one factor
  of each pair.
• When 2 gametes combine they will have 2 factors
  for each trait.
• The Law of Segregation states that a pair of
  factors is segregated or separated, during the
  formation of gametes.

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Law ofSegregation
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Law of Independent Assortment

• The factors for different characteristics are not
  connected.
• The law of independent assortment states that
  factors for different characteristics are
  distributed to gametes independently.

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Law of Independent Assortment
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Chromosomes and Genes

• Molecular Genetics is the study of the structure
  and function of chromosomes and genes.
• Because chromosomes occur in pairs, genes must
  also occur in pairs.
• One gene on each chromosome.
• Alternative forms of a gene is called an allele.
  
• Mendels factors alleles.
• Letters alleles.
• Capital letters dominant Lowercase letters
  recessive.

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Genetic Crosses

• Genotype and Phenotype
• Genotype genetic make-up of an organism.
• Consists of the alleles that the organisms
  inherits from its parents.
• Ex PP, Pp, or pp
• Phenotype the organisms appearance.

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Genotype

• Homozygous when both alleles of a pair are alike
  for that characteristic.
• Ex TT or tt
• Can be homozygous dominant (TT) or homozygous
  recessive (tt).
• Heterozygous when the two alleles in the pair are
  different for a characteristic.
• Ex Tt

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Probability

• Probability is the likelihood that a specific
  event will occur.
• Probability the number of times an event is
  expected to happen/ the number of opportunities
  for an event to happen.

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Monohybrid Cross

• A cross that involves one pair of contrasting
  traits monohybrid cross.
• Biologists use a diagram to aid them in
  predicting the probability that traits will be
  inherited by offspring Punnett Square.

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Homozygous X Homozygous

• Homozygous tall X homozygous short
• TT X tt
• Exampe

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Homozygous X Heterozygous

• Homozygous Tall X Heterozygous tall
• TT X Tt
• EX

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Heterozygous X Heterozygous

• Tt X Tt
• Ex

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Testcross

• Testcross when an individual of unknown
  genotype is crossed with a homozygous recessive
  individual.
• Will determine the genotype of any individual
  whose phenotype is dominant.

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Incomplete Dominance

• In the Pea-plant crosses, one allele was
  completely dominant over another complete
  dominance.
• Heterozygous plants and dominant homozygous
  plants are indistinguishable in phenotype.
• Ex Tt or TT would both be a tall plant.
• Sometimes the F1 offspring will have a phenotype
  in between that of the parents incomplete
  dominance.
• Occurs when 2 or more alleles influence the
  phenotype . (red flower X white flower pink)

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Incomplete dominance
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Codominance

• Codominance occurs when both alleles for a gene
  are expressed in heterozygous offspring.
• Neither allele is dominant or recessive, nor do
  the alleles blend in phenotype.

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Dihybrid Crosses

• A dihybrid cross is a cross between individuals
  that involves 2 characteristics (2 pairs of
  contrasting traits).
• Seed shape and Seed color.
• Rr X Yy

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DihybridCross