Basic Genetics

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Basic Genetics
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The Father of Genetics

• Gregor Mendel Austrian monk
• Carried out the first studies of heredity
• Successfully predicted how traits would be passed
• Studied the garden pea plant

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Basic terminology

• Heredity passing of characteristics from
  parents to offspring
• Gametes male and female sex cells
• Fertilization process where male and female sex
  cells unite
• Produces a zygote (fertilized egg)

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Cross pollination

• Mendel used to fertilize pea plants
• He would take pollen from one plant and dust on
  another

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Rule of unit factors

• Mendel concluded that two factors control each
  trait
• Each factor is called an allele
• An allele is the different forms of a gene
• Examples blue, green, brown are different
  alleles for the eye color gene

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Rule of dominance

• One allele is usually seen more often than the
  other
• Dominant alleles are observed more often
• Recessive alleles disappear
• To write alleles we abbreviate
• Capitol letter for the dominant
• Lower case letter for the recessive
• Always use the first letter of the dominant
  allele for both the dominant and the recessive
  alleles

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Genotype vs. Phenotype

• Phenotype the physical appearance
• Can be determined by looking at the organism
• Tall, short, blue eyes, brown hair
• Genotype the allele combination
• Cannot be determined by looking at the organism
• Can be homozygous (TT, tt, AA, aa)
• Can be heterozygous (Tt, Aa)

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Law of segregation

• Every individual has 2 alleles of each gene and
  when gametes are produced, each gamete receives
  one of these alleles
• During fertilization, gametes randomly pair to
  produce 4 combinations

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Punnett squares

• Shorthand way of finding possible genotypes of
  the offspring
• Monohybrid cross 4 boxes in square
• Dihybrid cross 16 boxes

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Punnett squares

• Parental gametes go along the top and down the
  side
• Inside the boxes, the possible combinations of
  the offspring

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Dihybrid crosses

• Involves two traits
• Follows the law of independent assortment
• Genes for different traits are inherited
  independently of each other

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Dihybrid Punnett squares

• Must use all possible combinations of alleles
  when setting up the Punnett square
• AATt x Aatt
• Must use the foil method to place gametes along
  the top and side
• Combine as usual for the combinations in the
  offspring

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Genotypic and phenotypic ratios

• Once Punnett square is complete, you must
  calculate the genotypic ratios and the phenotypic
  ratios