Intro to Genetics

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Intro to Genetics

• Mendel

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Mendel (Father of Genetics)

• Studied the inheritance of traits in pea plants
• Developed the laws of inheritance
• Mendel's work was not recognized until the turn
  of the 20th century

Gregor Mendel (1822-1884)
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Inheritance

• Mendel stated that physical traits are inherited
  as particles
• Mendel did not know that the particles were
  actually Chromosomes DNA

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Vocabulary

• Trait- any characteristic that can be passed
  from parent to offspring
• Heredity - passing of traits from parent to
  offspring
• Genetics - study of heredity
• Purebred one that always produces offspring
  with the same form of a trait as the parent.
  (homozygous)
• Hybrid has both forms of a trait (heterozygous)

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More Vocabulary

• Alleles - two forms of a gene (dominant
  recessive)
• Dominant - stronger of two genes expressed in the
  hybrid represented by a capital letter (R)
• Recessive - gene that shows up less often in a
  cross represented by a lowercase letter (r)
• Homozygous and purebred BB
• Heterozygous and hybrid Bb

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Eight Pea Plant Traits

• Seed shape --- Round (R) or Wrinkled (r)
• Seed Color ---- Yellow (Y) or  Green (y)
• Pod Shape --- Smooth (S) or wrinkled (s)
• Pod Color ---  Green (G) or Yellow (g)
• Seed Coat Color ---Gray (G) or White (g)
• Flower position---Axial (A) or Terminal (a)
• Plant Height --- Tall (T) or Short (t)
• Flower color --- Purple (P) or white (p)

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Generations

• P-Generation (Parents)
• F1 Generation (1st Generation of Offspring)
• F2 Generation (2nd Generation of Offspring)

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Punnett Squares

• The gene combinations that might result from a
  genetic cross can be determined by drawing a
  diagram known as the punnett square.

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Parent 1





Parent 2
Try these Tt x TT, Bb x bb, TT x tt , and Bb
x Bb
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Genotype and Phenotype

• Genotype is an organisms genetic makeup. For
  example Bb or BB or bb
• Phenotype is the physical characteristics or what
  they look like. For example if we were talking
  about eye color, the phenotype would be blue or
  brown eyes.
• If B brown eyes and b blue eyes
• Bbwould have brown eyes
• BB brown eyes
• bb blue eyes

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Lets PracticeGenotype or phenotype

• Blue
• Tt
• Tall
• Tt
• Short

• BB
• Brown
• Blonde
• Bb
• bb

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Beyond Dominant and Recessive Alleles

• Some alleles are neither dominant or recessive,
  and many traits are controlled by multiple
  alleles or multiple genes.
• Incomplete dominance one allele is not
  completely dominant over another. A red flower
  crossed with a white flower, produce pink
  flowers. (blending)
• Codominance Both alleles contribute to the
  phenotype of the organism. Black chicken crossed
  to a white chicken produce a black and white
  chicken

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Incomplete Dominance
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Codominance

• Two alleles are expressed (multiple alleles) in
  heterozygous individuals.
• Example blood type
• 1. type A IAIA or IAi
• 2. type B IBIB or IBi
• 3. type AB IAIB
• 4. type O ii