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Mendelian Genetics

Mendelian Genetics. Dihybrid Crosses. I. Law of Independent Assortment. A. Dihybrid Crosses 1. move from monohybrid to dihybrid cross 2. dihybrid-investigating the inheritance of two traits at one time 3. question to be asked is a. Are two genes inherited as a package?

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Mendelian Genetics

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  1. Mendelian Genetics Dihybrid Crosses

  2. I. Law of Independent Assortment • A. Dihybrid Crosses • 1. move from monohybrid to dihybrid cross • 2. dihybrid-investigating the inheritance of two traits at one time • 3. question to be asked is • a. Are two genes inherited as a package? • b. Are genes inherited independently passing on to the next generation without being affected by the first gene?

  3. B. Traits involved • 1. Seed shape R (round) vs. r (wrinkled) • 2. Seed color Y (yellow) vs. y (green)

  4. C. Parental generation • 1. true breeding round yellow X wrinkled green • 2. list parental genotypes • 3. list alleles carried in gametes of parental • 4. list genotype of F1 • 5. allow F1 to self-pollinate • 6. if traits are linked together would expect 3:1 ratio of round yellow : wrinkled green • 7. if traits inherited differently would expect something else

  5. D. Actual results

  6. E. Explanation • 1. Analyze trait as two monohybrid crosses • 2. Total number of round : wrinkled • 3. Total number of yellow : green • 4. both come out to a 3:1 ratio • 5. evidence that the two genes are inherited independently from one another • 6. the two traits travel from one generation to the next without influencing eachother • 7. they are not tied together • 8. What does this mean at the chromosomal level?

  7. 9. Two chromosomes are traveling on different chromosomes • a. nucleus of F1 portrayed at right • b. Two possible alignments for chromosomal pairs at metaphase I • c. these alignments result in the production of four different gametes produced in equal numbers

  8. 10. Produce Punnett square for cross

  9. 11. Complete square to determine phenotypic ratio

  10. F. Determining gametes-FOIL method • 1. meaning of foil • 2. examples of double hybrid • 3. examples using other combinations

  11. II. Fate of Mendel • A. discouraging • B. became head of monastery-very busy and little time for experiments • C. tried to replicate results using native hawkweed • 1. very different results • 2. requires pollen to begin development • 3. male and female nucleus do not fuse • 4. zygote is a haploid being

  12. Mendel and the boys

  13. Biology humor

  14. Old and discouraged Mendel

  15. III. Trihybrid crosses

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