Patterns of Inheritance

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Patterns of Inheritance

• Chapter 9

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Gregor Mendel

• Austrian monk
• Father of Modern Genetics
• Famous for his work with peas

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Mendels Peas
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Cross-Pollinating
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General Background Vocabulary

• Self-pollination pollen from flower fertilizes
  the same plant
• True-breeds pure gene lines offspring match
  parent due to self-fertilization)
• Cross-pollination pollen will fertilize a
  different plant
• Hybrid Offspring that result from a cross
  between organisms with different traits express
  a combination of traits from
• Character heritable feature that varies among
  individuals (ex. seed color)
• Trait possible variations for a particular
  character (ex. yellow seeds vs. green seeds)

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Mendels Crosses

• Mendel noticed that one trait was always
  expressed over the other in the F1 offspring
• However, trait that disappeared always reappeared
  in about 25 of the F2 offspring.

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Mendels Initial Conclusion

• Biological inheritance is determined by chemical
  factors passed from one generation to the next
• Geneticists now refer to these heritable factors
  as genes
• Genes can come in more than one form, each form
  is an allele ex. B or b (The B gene w/ 2
  alleles)
• Additional relevant terminology
• Homozygous two identical alleles (AA or aa)
• Heterozygous two different alleles (Aa)
• Phenotype Physical appearance
• Genotype Genetic make-up
• Homozygous dominant (AA)
• Homozygous recessive (aa)
• Heterozygous (Aa)

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The Principles Dominance Segregation

• Dominance Certain alleles will be expressed
  over others, the expressed alleles are dominant
  to the unexpressed recessive alleles
• Segregation Each parent carries two alleles for
  each gene. During meiosis, the pairs are
  separated to that only one allele is sent to the
  offspring in the gamete from each parent.

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Genetics Probability

• Probability is the likelihood of an event
  happening
• Consider flipping a coin
• Likelihood of flipping heads 50
  
• (1 of 2 possibilities)
• Likelihood of flipping heads twice?
• 50 x 50 25
• To predict outcomes of genetic crosses we use
  punnett squares

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The Test Cross
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Exploring Mendelian Genetics

• Does segregation of one set of alleles influence
  the segregation of another pair of alleles?
• Mendels Two Factor (dihybrid) Crosses
• Followed two traits at a time.
• Same method as his original single-factor crosses
• Cross-pollinated to produce the F1 and allowed
  them to self-pollinate
• Mendel found that alleles for different traits
  did not influence each others segregation. This
  is referred to as the principle of independent
  assortment.

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Pedigrees

• Pedigrees are like genetic family trees. They
  are used to show the inheritance of traits within
  families and to predict genotypes and/phenotypes
  of certain individuals.
• The following key explains the symbols and layout
  of a typical pedigree

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Autosomal Dominant Pedigree
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Autosomal Recessive Pedigree