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Trihybrid Cross quiz

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  • What is a trihybrid cross?
    A trihybrid cross analyzes the inheritance of three traits simultaneously, similar to a dihybrid cross but with an additional gene.
  • How do you identify wild type and mutant alleles in fruit fly genetics?
    Wild type alleles are marked with a plus sign (+), while mutant alleles lack the plus sign.
  • What is the purpose of crossing parental fruit flies with opposite phenotypes in a trihybrid cross?
    Crossing parentals with opposite phenotypes allows easy tracking of allele transmission and produces a heterozygous F1 generation.
  • What does the dot notation in genetic diagrams indicate?
    The dot notation indicates that it is unknown whether the genes are linked or unlinked.
  • What is a test cross and what genotype is used for the tester?
    A test cross involves crossing the F1 heterozygote with a homozygous recessive individual.
  • How do you determine if a gamete is parental or recombinant?
    Compare the gamete to the parental types; if it matches, it is parental, otherwise it is recombinant.
  • What is the formula for calculating recombination frequency?
    Recombination frequency (rf) is calculated as the number of recombined offspring divided by the total number of offspring.
  • What recombination frequency indicates that genes are linked?
    Genes are considered linked if their recombination frequency is less than 50%.
  • How do you use recombination frequencies to map gene order?
    Place the genes with the highest recombination frequency farthest apart and use the lowest frequency to determine which gene is closest to another.
  • Why might the sum of two map distances not equal the direct recombination frequency between two genes?
    Double crossovers can occur, which are not accounted for in single recombination frequency calculations, requiring adjustment by counting double crossovers twice.
  • What is the significance of double crossovers in genetic mapping?
    Double crossovers affect recombination frequency calculations and must be counted twice to accurately determine map distances.
  • How do you identify which allele recombined in a recombinant gamete?
    Compare the recombinant gamete to parental types and identify which allele differs, indicating where recombination occurred.
  • What is the correct order for writing gene maps after determining linkage and distances?
    Write the gene order based on calculated map distances, not the order given in the question, using the highest and lowest recombination frequencies.
  • What pattern is commonly seen in trihybrid cross offspring tables?
    A common pattern is two parental types and multiple recombinant types, often grouped in fours and twos.
  • Why is practicing the identification of parental and recombinant gametes important?
    It is essential for accurately calculating recombination frequencies and constructing chromosome maps, which are frequently tested in genetics exams.