Mendelian Genetics Dihybrid Crosses I Law of Independent
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? • b. Are genes inherited independently passing on to the next generation without being affected by the first gene?
B. Traits involved • 1. Seed shape R (round) vs. r (wrinkled) • 2. Seed color Y (yellow) vs. y (green)
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 F 1 5. allow F 1 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
D. • Actual results Round yellow 315 parental Wrinkled yellow 101 recombinant Round green 108 recombinant Wrinkled green 32 parental
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?
9. Two chromosomes are traveling on different chromosomes • a. nucleus of F 1 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
10. Produce Punnett square for cross Male/fem RY ale RY RRYY Ry r. Y ry
11. Complete square to determine phenotypic ratio offspring Expected Actual mendelia numbers ratio n ratio Round yellow Round green Wrinkled yellow Wrinkled green
F. Determining gametes-FOIL method • 1. meaning of foil • 2. examples of double hybrid • 3. examples using other combinations
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
Mendel and the boys
Biology humor
Old and discouraged Mendel
III. Trihybrid crosses
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