1. INCOMPLETE DOMINANCE AND CODOMINANCE 1

2. INCOMPLETE DOMINANCE  F1 hybrids in betweenphenotypes  F1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties.  Example:snapdragons (flower)  Example: snapdragons (flower)  red (RR) x white (rr)  RR = red flower  rr = white flower 2 R R rr

3. INCOMPLETE DOMINANCE 3RrRrRrRr R Rr All Rr = pink (heterozygous pink) produces the F 1 generation r

4. INCOMPLETE DOMINANCE 4

5. CODOMINANCE  Two alleles are expressed equally in multiple alleles in heterozygous individuals.  Example: blood type  1.type A= I A I A or I A i  2.type B= I B I B or I B i  3.type AB= I A I B (equally expressed)  4.type O= ii (recessive alleles) 5

6. CODOMINANCE PROBLEM  Example: homozygous male Type B (I B I B ) X heterozygous female Type A (I A i) 6 IAIBIAIB IBiIBi IAIBIAIB IBiIBi 1/2 = I A I B (A & B = equally expressed) 1/2 = I B i (B dominant over i) IBIB IAIA i IBIB

7. ANOTHER CODOMINANCE PROBLEM 7 Example:Example: male Type O (ii) x female type AB (I A I B ) IAiIAiIBiIBi IAiIAiIBiIBi 1/2 = I A i 1/2 = I B i i IAIA IBIB i

8. CODOMINANCE Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? boy - type O (ii) X girl - type AB (I A I B ) 8

9. CODOMINANCE Answer: 9

10. SEX-LINKED TRAITS  Traits (genes) located on the sex chromosomes  Sex chromosomes are X and Y  XX genotype for females  XY genotype for males  Many sex-linked traits carried on X chromosome 10

11. SEX-LINKED TRAITS 11 Sex Chromosomes XX chromosome - femaleXy chromosome - male fruit fly eye colour Example: Eye colour in fruit flies

12. SEX-LINKED TRAIT PROBLEM  Example: Eye colour in fruit flies  (red-eyed male) x (white-eyed female) X R Y x X r X r  Remember: the Y chromosome in males does not carry these traits.  RR = red eyed  Rr = red eyed  rr = white eyed  XY = male  XX = female 12 XRXR XrXr XrXr Y

13. SEX-LINKED TRAIT SOLUTION: 13 X R X r X r Y X R X r X r Y 50% red eyed female 50% white eyed male XRXR XrXr XrXr Y

14. FEMALE CARRIERS 14

15. GENETIC PRACTICE PROBLEMS 15

16. BREED THE P 1 GENERATION tall (TT) x dwarf (tt) pea plants 16 T T tt

17. SOLUTION: 17 T T tt Tt All Tt = tall (heterozygous tall) produces the F 1 generation tall (TT) vs. dwarf (tt) pea plants

18. BREED THE F 1 GENERATION tall (Tt) vs. tall (Tt) pea plants 18 T t Tt

19. SOLUTION: 19 TT Tt tt T t Tt produces the F 2 generation 1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt 1:2:1 genotype 3:1 phenotype 3:1 phenotype tall (Tt) x tall (Tt) pea plants