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Dihybrid Crosses: Predicting Offspring Traits

Learn how to use dihybrid crosses and Punnett squares to predict the probability of offspring having two traits at the same time. Explore incomplete dominance, codominance, multiple alleles, and polygenic traits.

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Dihybrid Crosses: Predicting Offspring Traits

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  1. Warm-up Turn in your meiosis simulation activity and your punnett piggy activity sheets

  2. 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.

  3. 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?

  4. Step 1 • Draw a box and divide it into 16 squares.

  5. 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.

  6. 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!

  7. Step 4 YR Yr yR 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

  8. Step 5 • Do the cross • Remember to keep all of one letter together and all of the 2nd letter together. YR Yr yR yr YYRR YYRr YR YyRR YyRr YyRr YYRr YYrr Yyrr Yr YyRR YyRr yR yyRR yyRr yyrr YyRr Yyrr yyRr yr

  9. Step 6 • Go through the results and determine what the phenotype of each offspring would be YR Yr yR yr YYRR Yellow round YYRr Yellow, round YyRR Yellow, round YyRr Yellow, round YR YYRr Yellow, round YYrr Yellow,wrinkled Yyrr Yellow, wrinkled YyRr Yellow, round Yr YyRR Yellow, round YyRr Yellow, round yyRR Green, round yyRr Green, round yR YyRr Yellow, round Yyrr Yellow, wrinkled yyRr Green, round Yyrr Green, wrinkled yr

  10. Step 7 • Figure out the phenotypic ratio or answer whatever question they ask you. • 9:3:3:1 • Example: what are the chances of having a yellow and wrinkled pea? • 3/16 YR Yr yR yr YYRR Yellow round YYRr Yellow, round YyRR Yellow, round YyRr Yellow, round YR YYRr Yellow, round YYrr Yellow, wrinkled Yyrr Yellow, wrinkled YyRr Yellow, round Yr YyRR Yellow, round YyRr Yellow, round yyRR Green, round yyRr Green, round yR YyRr Yellow, round Yyrr Yellow, wrinkled yyRr Green, round Yyrr Green, wrinkled yr

  11. Incomplete Dominance • Heterozygous offspring show a phenotype that is in between the phenotypes of the two homozygous parents

  12. 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.

  13. Codominance Both alleles in the heterozygote express themselves fully. Example: Blood types Roan cattle

  14. Codominance And a person homozygous for Type B blood A person homozygous for Type A blood Will produce a child that will demonstrate both Type A and Type B blood (Type AB)

  15. Summary

  16. 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

  17. Polygenic Traits • Polygenic Traits- Traits controlled by two or more genes that interact. • Ex: Human Eye Color and skin pigment

  18. In summary:

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