1. Monohybrid Crosses Vs. Dihybrid Crosses MENDELIAN GENETICS

2. Dihybrid Cross Mendel’s Law of Independent Assortment - inheritance pattern of one trait will not affect the inheritance pattern of another Independent assortment occurs during meiosis Use Punnett Square to determine probability of how the alleles of 2 traits are being inherited at a time

4. Dihybrid Cross Cross Step 1: Identify Alleles of Traits In snapdragons, tallness (T) is dominant to dwarfness (t). Flowers can can be red (R), white (r), or pink (Rr) in color. A dwarf, pink snapdragon is crossed with a plant homozygous for tallness & for red flowers. Give the possible genotypes and corresponding phenotypes for all of the possible F 1 generation.

5. Step #2: Determine Genotypes of Parents dwarf, pink snapdragon is crossed with a plant homozygous for tallness & red flowers dwarf, pink = ttRr homozygous tall, red = TTRR ttRr x TTRR

6. Step #3: Determine Genotypes of Gametes dwarf, pink snapdragon is crossed with a plant homozygous for tallness & red flowers Use FOIL method dwarf, pink = t t R r tR tr tR tr

7. Step #3: Determine Genotypes of Gametes dwarf, pink snapdragon is crossed with a plant homozygous for tallness & red flowers dwarf, pink = ttRr homozygous tall, red = TTRR tRtrtR tr TR

8. gametes from TALL red parent tR tr tR tr pink gametes from dwarf pink parent TtRR TtRr TtRR TtRr TtRR TtRr TtRR TtRr TtRR Step #4: Punnett Square Punnett square determines the genotypes of the offspring

9. TtRR TtRr TtRR TtRr TtRR TtRr TtRR TtRr TtRR Step #5: Identify Phenotype Ratios in Offspring Tall, red = 8/16 Tall, pink = 8/16 Tall, white = 0/16 Short, red = 0/16 Short, pink = 0/16 Short, white = 0/16

10. Dihybrid Punnett Square Practice: Example 1 cross a heterozygous round, green pea with a wrinkled, heterozygous yellow pea. 1. identify the alleles of traits R = round r = wrinkled 2. show cross of the two parents Rryy x rrYy 3. show possible genotypes of gametes use FOIL method from parent 1: Ry, ry, Ry, ry from parent 2: rY, ry, rY, ry Y = yellow y = green

11. Dihybrid Punnett Square Practice: Example 1 cross a heterozygous round, green pea with a wrinkled, heterozygous yellow pea. 4. create & complete Punnett Square for Rryy x rrYy

12. Dihybrid Punnett Square Practice: Example 1 cross a heterozygous round, green pea with a wrinkled, heterozygous yellow pea. 4. create & complete Punnett Square for Rryy x rrYy

13. Dihybrid Punnett Square Practice: Example 1 cross a heterozygous round, green pea with a wrinkled, heterozygous yellow pea. 5. determine phenotypic ratiosGenotypePhenotype ¼ RrYy ¼ Round, Yellow Yellow ¼ Rryy ¼ Round, green green ¼ rrYy ¼ wrinkled, Yellow Yellow ¼ rryy ¼ wrinkled, green green

14. Dihybrid Punnett Square Practice: Example 2 In guinea pigs, allele for short hair (S) is dominant to long hair (s), & allele for black hair (B) is dominant over allele for brown hair (b). Cross 2 parents that are heterozygous for both traits?

15. Dihybrid Punnett Square Practice: Example 2 In guinea pigs, allele for short hair (S) is dominant to long hair (s), & allele for black hair (B) is dominant over allele for brown hair (b). Cross 2 parents that are heterozygous for both traits? 1. identify the alleles of traits S = short hair s = long hair 2. show cross of the two parents SsBb x SsBb 3. show possible genotypes of gametes from parent 1: SB, Sb, sB, sb from parent 2: SB, Sb, sB, sb B = black hair b = brown hair

16. Dihybrid Punnett Square Practice: Example 2 SBSbsBsb SBSSBBSSBbSsBBSsBb SbSSBbSSbbSsBbSsbb sBSsBBSsBbssBBssBb sbSsBbSsbbssBbssbb What is the probable offspring phenotype ratio for a cross involving 2 parents that are heterozygous for both traits? 9/16 Black, Short hair 3/16 Black, long hair 3/16 brown, Short hair 1/16 brown, long hair