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Warm-up Turn in your meiosis simulation activity and your punnett piggy activity sheets Dihybrid crosses Dihybrid crosses are punnett squares used to predict the probability of an offspring having 2 traits at the same time. Ex: What are the chances of my baby having brown eyes AND blond hair. Dihybrid crosses Yellow seeds (Y) are dominant to green seeds (y) Round seeds (R) are dominant to wrinkled seeds (r) If both parents are heterozygous for both traits, what are the genotypic and phenotypic ratios of the offspring? Step 1 Draw a box and divide it into 16 squares. Step 2 Determine the genotypes of the parents YyRr x YyRr Ex: cross two pea plants that are heterozygous for yellow peas and round peas. Yellow is dominant to green and round is dominant to wrinkled. Step 3 Determine all of the possible gamete combinations for each parent by using the F.O.I.L. method FOIL= first, outside, inside last Ex: YyRr First- YR Outside- Yr Inside- yR Last- yr Principle of independent Assortment! Step 4 YR Write all of the possible combinations of alleles on the sides and top of the punnett square. YR Yr yR yr YR Yr yR yr Yr yR yr Step 5 Do the cross Remember to keep all of YR one letter together and all of the 2nd letter Yr together. yR yr YR Yr yR yr YYRR YYRr YyRR YyRr YYRr YYrr YyRr Yyrr YyRR YyRr yyRR yyRr YyRr Yyrr yyRr yyrr Step 6 Go through the results and determine what the YR phenotype of each offspring would be Yr yR yr YR Yr yR yr YYRR YYRr YyRR YyRr Yellow round Yellow, round Yellow, round Yellow, round YYRr YYrr YyRr Yyrr Yellow, round Yellow,w rinkled Yellow, round Yellow, wrinkled YyRR YyRr yyRR yyRr Yellow, round Yellow, round Green, round Green, round YyRr Yyrr yyRr Yyrr Yellow, round Yellow, wrinkled Green, round Green, wrinkled Step 7 Figure out the phenotypic ratio or YR answer whatever question they ask you. 9:3:3:1 Yr Example: what are the yR chances of having a yellow and wrinkled yr pea? 3/16 YR Yr yR yr YYRR YYRr YyRR YyRr Yellow round Yellow, round Yellow, round Yellow, round YYRr YYrr YyRr Yyrr Yellow, round Yellow, wrinkled Yellow, round Yellow, wrinkled YyRR YyRr yyRR yyRr Yellow, round Yellow, round Green, round Green, round YyRr Yyrr yyRr Yyrr Yellow, round Yellow, wrinkled Green, round Green, wrinkled Incomplete Dominance Heterozygous offspring show a phenotype that is in between the phenotypes of the two homozygous parents Incomplete Dominance R R W RW RW W RW RW Crossing homozygous parents to produce F1 generation THE ALLELES REMAIN DISTINCT; ONLY THE PHENOTYPE APPEARS BLENDED. Codominance Both alleles in the heterozygote express themselves fully. Example: Blood types Roan cattle Codominance A person homozygous for Type A blood And a person homozygous for Type B blood Will produce a child that will demonstrate both Type A and Type B blood (Type AB) Summary Incomplete Dominance Codominance Traits are blended (red + white = pink) Both traits are expressed (A + B = AB) Multiple Alleles A gene that has more than two possible alleles, though only two alleles are present at a time. EX: Blood Type A, B, O Polygenic Traits Polygenic Traits- Traits controlled by two or more genes that interact. Ex: Human Eye Color and skin pigment In summary: Multiple Alleles Polygenic Trait More than two possible alleles, but only two present at a time. Single trait controlled by more than one gene.
