1. BIOLOGY 12 Two-Trait Inheritance Dihybrid Cross

2. Remember Mendel’s Peas… CharacterTraitAllele Seed shapeRoundR Wrinkledr Seed colourYellowY Greeny

3. Mendel’s hypothesis was that each trait was independent of the other this means that one allele does not have an effect on another allele independent assortment – the chromosomes will randomly align and divide there is no connection between the two different chromosomes

5. Law of Independent Assortment it appears that the inheritance of seed shape has no influence over the inheritance of seed colour the two characters are inherited INDEPENDENTLY the pairs of alleles that control these two characters assort themselves independently

6. Determining Gametes when dealing with two homozygous genotypes, the gametes will be the same example: RRYYx rryy gametes: RY, RY, ry, ry note: the gametes do not need the capital first

7. Determining Gametes when dealing with heterozygous genotypes, you use FOIL (think math!) example: RrYy R r Y y First and Outside RY and Ry Inside and Last rY and ry Possible Gametes: RY, Ry, rY and ry

8. Practice complete the following Punnett square using the following cross: AaBb x AaBb AB Ab aB ab AB Ab aB ab

10. How Good Were Mendel’s Results We could expect What Mendel observed 556 x 9/16 round yellow313315 556 x 3/16 round green104108 556 x 3/16 wrinkled yellow104101 556 x 1/16 wrinkled green3532

11. Practice In watermelons the genes for green color and for short shape are dominant over their alleles for striped color and for long shape. Suppose a plant with long striped fruit is crossed with a plant heterozygous for both these characters. What phenotypes would this cross produce and in what ratios?

12. Practice A heterozygous tall, homozygous green pea plant is crossed with a heterozygous tall, heterozygous yellow plant. What is the probability that the offspring will be short and green?

13. Single Trait Practice In dogs, wire hair is due to a dominant gene (W), and smooth hair is due to its recessive allele. If a homozygous wire-haired dog is mated with a smooth-haired dog, what would be possible phenotypes of the offspring?

14. Single Trait Practice Two wire-haired dogs (W?) are mated, and among the offspring of their first litter is a smooth-haired pup. If these two wire-haired dogs mate again, what is the chance that they will produce another smooth-hair pup? What are the chances that the pup will be wire-haired?

15. Two Trait Practice A female dog is heterozygous for both fur length and colour. She shows long, brown fur. Her mate shows short, white fur. Determine the gametes of each dog. What is the probability that the pup will be just like its mother?

16. Two Trait Practice In humans, the presence of freckles is due to the dominant gene (F), and the non-freckled condition is due to its recessive allele (f). Dimpled cheeks (D) is dominant to non-dimpled cheeks (d). Two persons with freckles and dimpled cheeks have two children. One has freckles but no dimples (F?dd), one has dimples but no freckles (ffD?). What are the genotypes and phenotypes of the parents?