Genetics and Inheritance

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Genetics and Inheritance

• The Scientific Study of Genes and the Inheritance
  of Traits

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• Gregor Mendel (1860) Father of Genetics
• Experimented with pea plants
• Used self-fertilization (asexual reproduction)
  and cross-fertilization methods (sexual
  reproduction)
• chose simple traits to follow (flower color,
  height, seed color, seed texture etc.)

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Key Terms To Know

• Trait any characteristic that can be passed
  from parents to their offspring
• Gene genetic material on a chromosome that
  contains the instructions for creating a
  particular trait
• Allele one of several varieties of a gene, an
  alternate form of the same gene for a given
  trait example A or a (same letter, different
  case)
• Locus the location on a chromosome where a gene
  is located

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Homologous Pairs
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Monohybrid Crosses

• Monohybrid Cross a cross involving only a
  single allele responsible for a trait each
  parent contributes information for the trait
  (ex. Aa X AA)

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Trait Characteristics

• Dominant trait the trait that gets expressed in
  a monohybrid cross where the mode of inheritance
  is Complete Dominance shown by a capital letter
  A
• Recessive trait the trait that is hidden in a
  monohybrid cross where the mode of inheritance is
  Complete Dominance shown by a lower case letter
  a

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Allele Pairing

• Homozygous the two alleles for a trait that an
  organism has are identical ex Homozygous
  Dominant AA , Homozygous Recessive aa
• Heterozygous the two alleles coding for a trait
  are different ex Aa

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Genotype vs. Phenotype

• Genotype the actual genetic information, all
  the alleles that an organism possesses (the
  actual letters)
• Phenotype physical appearance based on alleles

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Mendels First Law of Heredity

• Law of Dominance When a trait is Completely
  Dominant over another trait, then that dominant
  allele controls the gene pair. In the
  heterozygous form (Aa) the dominant trait only
  gets expressed. The recessive allele gets hidden.

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Mendels Second Law of Heredity

• Law of Segregation Pairs of alleles separate
  during the formation of the gametes (sex cells)
  during Meiosis I. Therefore each gamete will
  contain one allele for each gene.

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Meiosis and Independent Assortment
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Mendels Third Law Of Heredity

• Law of Independent Assortment Gene pairs
  separate into the gametes both independently and
  randomly of each other.
• The rules of probability are used to describe how
  the different chromosomes and their alleles from
  parents assemble into gametes and ultimately into
  offspring.

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PUNNETT SQUARES

• Used to track a trait from parents to offspring.
• Shows possible ratios for offspring outcomes.
• P Generation Parents
• F1 Generation Offspring from the cross of the
  parents
• F2 Generation Offspring produced from crosses
  among
  the F1
• F filial, refers to sons and daughters

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Monohybrid Cross
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Punnett Square Rules

• 1. Make a key show dominant and recessive
  alleles
• 2. Properly label parents genotypes, place them
  on the outside of the punnett square
• 3. Correctly perform the cross
• 4. Interpret the results determine ratios

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Test Crosses

• Suppose we have two Tall pea plants
• T tall
• t short

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What are the possible genotypes for each plant?

• tt For A Short Plant
• TT OR Tt For a Tall Plant

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Test Cross cross the tall plant (TT or Tt) with
a short one (tt)

• If any recessive phenotypes show up in the next
  generation, the unknown genotype MUST be
  Heterozygous
• Homozygous tall x short TT x tt Heterozygous
  Tall x short Tt x tt

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