Plant breeding lecture 5 & 6

  1. What is true-breeding varieties?
    self-fertilized plants that produce only progeny like themselves
  2. What is complete dominance?
    • Expression of a member of an allele pair at
    • all times (homozygous or heterozygous
    • condition) at the exclusion of a recessive
    • allele
  3. What is additive gene action?
    • The effect when each additional gene/allele
    • enhances the expression of the trait by
    • equal increments
    • aa = 0
    • Aa = 1
    • AA = 2
  4. What is over dominance gene action?
    • When each allele at a locus produces a
    • separate effect on the phenotype, and their
    • combined effect exceeds the independent
    • effect of the alleles
    • aa = 1
    • AA = 2
    • Aa = 4
  5. What is Recessiveness ?
    • Expression of a member of an allele pair only
    • in the homozygous condition - not in the
    • presence of a dominant allele
    • aa
  6. What is incomplete or partial dominance?
    • the phenotype of the heterozygous genotype is intermediate between the phenotypes of the homozygous genotypes Expression of the heterozygote distinct from the two homozygotes
    • AA ≠ Aa ≠ aa
  7. What is Pleiotropy ?
    • One gene controlling the expression of more
    • than one trait
    • EX:
    • Plant Height gene may affect Lodging
    • Chlorophyll gene (Leaf Color) may affect
    • Maturity and Drought/Heat Tolerance
  8. What is Epistasis?
    • Interaction between or among non-allelic
    • genes
  9. What is the principle of segregation?
    • In the formation of gametes, the paired
    • hereditary determinants (genes) segregate in
    • such a way that each gamete is equally likely
    • to contain either member of the pair
  10. what is a monohybrid cross?
    is a mating between two individuals with different alleles at one genetic locus of interest.
  11. What is the Principle of Independent Assortment?
    Segregation of the members of any pair of alleles is independent of the segregation of other pairs in the formation of reproductive cells
  12. What are the laws of probability: the addition rule?
    • The probability of the realization of one or the other of two mutually exclusive events, A or B, is the sum of their separate probabilities
    • • Mendelian patterns of inheritance follow laws of probability
    • • Prob {WW or Ww} = Prob {WW} + Prob{Ww} = 0.25 + 0.50 = 0.75
  13. Difference between quantitative and qualitative traits?
    • Quantitative traits are more influenced by
    • the environment than are qualitative traits
    • Ex: 
    • Yield
    • Lind—15-50 bu/a
    • Pullman—70-150 bu/a
  14. Things that effect Quantitative traits:
    • Values depend on what type of gene action
    • we are seeing
    • Depends on the number of loci involved in
    • the trait expression
    • Environmentally controlled
    • Continuous variation exhibited
  15. What is transgressive segregation?
    • The trait value of some progeny fall outside
    • the range of the parental lines
    • Important in breeding to obtain segregates
    • that are superior to either parent
    • Results from new combinations of multiple
    • genes with more positive effects than in
    • either parental line
  16. When do you first see transgressive segregation phenotypes?
    • Appearance in F2 or later generations of
    • individuals with more extreme phenotypes
    • than either parent
  17. How can you tell the difference between qualitative and quantitative traits by looking at histograms?
    • quantitative traits are normally distributed 
    • qualitative traits are a yes or no bar chart
  18. What is epistasis really doing?
    • refers to any type of gene interaction that results in the F2 dihybrid ratio of 9:3:3:1 being modified into some other ratio
    • In a more general sense, it means that one
    • gene is masking the expression of the other
  19. What is a testcross?
    • a cross between an organism of dominant phenotype (genotype unknown) and an
    • organism of recessive phenotype (genotype known to be homozygous recessive)
  20. What does a testcross tell us?
    • the relative proportion of the different
    • gametes produced by the heterozygous parent can be observed directly in the proportion of phenotypes of the progeny, because the recessive parent contributes only recessive alleles
  21. Gene Recombination during meiosis:
    • Independent Assortment Affects genes of interest on different chromosomes
    • Crossing Over Affects genes of interest that are linked on the same chromosome
  22. What does a Chi-Square Analysis tell us?
    • The test of goodness of fit = test analyzes
    • whether observed data agree with theoretical
    • expectation
  23. What is the equation for Chi-Square?
    • χ2 = ∑(observed – expected)2 / expected
    • A value of χ2 = 0 means that the observed
    • numbers fit the expected numbers perfectly
    • A conventional measure of goodness of fit is a
    • value called chi-square, χ2
  24. What does it mean to be Statistically significant?
    refers to the magnitude of the difference between the observed and the expected numbers
Card Set
Plant breeding lecture 5 & 6
plant breeding