Introduction to Genetics

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Introduction to Genetics

• The Work of Gregor Mendel

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Genetics

• Scientific study of heredity
• Gregor Mendel
• Born in 1822 in Czech Republic
• Worked in monastery garden while teaching H.S.
  (math science)
• Worked w/ true-breeding pea plants
• If allowed to self-pollinate, produce offspring
  identical to themselves

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Genes and Dominance

• Mendel studied 7 traits
• Specific characteristic that varies from one
  individual to another color, height
• Each trait had two contrasting characters greed
  seeds vs. yellow
• Crossed true-breeding plants of each type to
  opposing character

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Genes and Dominance

• True-breeding yellow seed X True-breeding green
  seed
• Original pair of plants P (parental) generation
• Offspring F1 (first filial)
• Offspring of crosses between parents w/ different
  traits hybrids

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• What did the F1 hybrids look like? Did they look
  like a blend of both parents? No!
• All F1 offspring only showed the character of one
  parent.

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Mendels Two Conclusions

• 1. Biological inheritance is determined by
  factors that are passed on from one generation to
  the next
• Genes chemical factors that determine traits

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• Each trait that Mendel studied was controlled by
  one gene that occurred in two contrasting forms
• Ex Gene for Plant Height One form for tall
  one for short
• Alleles different forms of a gene

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• 2. Principle of Dominance some alleles are
  dominant and others are recessive
• If there is a dominant present, that form is
  shown
• If there are two recessive present, the recessive
  is shown

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Segregation

• Did the recessive alleles disappear, or were they
  still present ?
• To find the answer, he allowed F1 generation
  plants to self-pollinate to create an F2
  generation
• What happened?
• Traits reappeared. ¼ of the F2 plants showed the
  recessive allele

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Segregation, contd

• Law of Segregation
• Two alleles separate from each other so that each
  gamete carries only a single copy of each gene
• Ex Fig. 11-5

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Introduction to Genetics

• Genetics and Probability

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Genetics and Probability

• Probability
• The likelihood that a particular event will occur
• Ex tossing a quarter
• Heads 1 in 2
• Tails 1 in 2
• 3 tails in a row ½ x ½ x ½ 1/8
• Principles can be used to predict outcome of
  genetic crosses

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Genetic Vocabulary

• Character
• Detectable inheritable feature of an organism
• Trait
• Variant of inheritable character
• allele / alleles

• Dominant
• Capital letter (SS)
• Recessive
• Lower case (ss)
• Two alleles for each character
• Mom and dad

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Genetic Vocabulary

• Genotype
• The genetic makeup of an organism
• Written in letter format
• PP, pp, Pp

• Phenotype
• The physical traits of an organism

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Genetic Vocabulary

• Homozygous
• Having two identical alleles for a given trait
• PP
• ss

• Heterozygous
• Having two different alleles for a given trait
• Pp
• Ss

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Pea Traits
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Basic Crosses
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Recessive/Dominant

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