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Patterns of Inheritance


Patterns of Inheritance Chapter 9 Gregor Mendel Austrian monk Father of Modern Genetics Famous for his work with peas Mendel s Peas Cross-Pollinating General ... – PowerPoint PPT presentation

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Title: Patterns of Inheritance

Patterns of Inheritance
  • Chapter 9

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

Mendels Peas
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)

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.

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
  • 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)

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.

Genetics Probability
  • Probability is the likelihood of an event
  • 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

The Test Cross
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

  • 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

Autosomal Dominant Pedigree
Autosomal Recessive Pedigree
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