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Dihybrid Inheritance. Dihybrid inheritance refers to the simultaneous inheritance of two characters. Mendel’s experiment. Mendel investigated the inheritance of seed shape (round v wrinkled) and seed colour (green v yellow) at the same time.
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Dihybrid Inheritance Dihybrid inheritance refers to the simultaneous inheritance of two characters
Mendel’s experiment • Mendel investigated the inheritance of seed shape (round v wrinkled) and seed colour (green v yellow) at the same time. • From his monohybrid crosses he knew that round seeds were dominant to wrinkled seeds and yellow seeds were dominant to green seeds. • He chose to cross plants that were pure breeding for both dominant features (round and yellow seeds) with plants that were pure breeding for both recessive features (wrinkled and green seeds)
Results F1 offspring 100% plants with round and yellow seeds Parents plants with round x plants with wrinkled and yellow seeds and green seeds F1 intercrossplants with round x plants with round and yellow seeds and yellow seeds F2 offspring Total 556 seeds collected from F2 plants Ratio 315 9 round and yellow seeds 108 3 round and green seeds 101 3 wrinkled and yellow seeds 32 1 wrinkled and green seeds However, the ratio of dominant to recessive features is still 3:1
Explanation of Mendel’s results • Let the allele for round seeds be R and the allele for wrinkled seeds be r • Let the allele for yellow seeds be Y and the allele for green seeds be y Parents Phenotyperound x wrinkled yellowseeds greenseeds GenotypeRR YY rryy Gametes F1 offspring RY RY ry ry
F1 intercross Parents phenotype round, yellow seeds x round, yellow seeds genotypeRr Yy Rr Yy Gametes RY Ry rY ry RY Ry rY ry What are the genotypes and phenotypes of the F2 offspring and in what ratio?
F2 offspring genotypes phenotypes expected observed RRYY (1)RrYy (4) yellow, round RRYy (2) RrYY (2) yellow, round 9 315 RRyy (1) Rryy (2) round, green 3 108 rrYY (1) rrYy (2) wrinkled, yellow 3 101 rryy (1) wrinkled, green 1 32
Allowing for statistical error, Mendel’s results were a reasonable approximation to the expected 9:3:3:1 ratio • Each of a member of an allelic pair may combine randomly with either of another pair • A test cross can be performed to check the possible genotypes of a plant producing round, yellow seeds (RRYY, RrYY, RrYy, RRYy) by crossing the plants with a homozygous recessive plant with wrinkled green seeds genotype rryy • What phenotypes and genotypes would the offspring possess from the 4 crosses, and in what ratios?
