Parent The red and white Incomplete color alleles of dominance Mirabilis jalapa show incomplete heterozygotes are intermediate R2R2 red white Heterozygous snapdragons(R/r) 1 generation The offspring of a cross between have an intermediate red(R'R')and color, pink white(RR2)have an intermed iate (pink phenotype. Crossing two pink RIR2 ink snapdragons gives a 1 RR: 2R/r: 1r/r F2 generation Selfing the RR2 progeny ratIo. heterozygotes gives F2 progeny with a phenotypic ratio of 1 red RR1 RR2 RR2 R2R2 2 pink: 1 white. red pink pink white 14 1h2 14
• Incomplete dominance: heterozygotes are intermediate. • Heterozygous snapdragons (R/r) have an intermediate color, pink. • Crossing two pink snapdragons gives a 1 R/R: 2R/r: 1r/r progeny ratio. 4.1
Incomplete dominance AA×aa Gametes A F1( (all identical))?Aa×dAa a 2 A AAAa Aaaa 1 AA(red): 2 Aa(pink): 1 aa(white)
Incomplete dominance in dihybrid crosses One gene with partial dominance, one gene with complete dominance: F2= 3: 6: 3: 1: 2: 1 3/4B/ (1AAB-=3/16 114AA 1/4b/b (2)AAbb=116 3/4B/ (3)AaB/-=6/16 1/2Aa 14b/b (4)Aab/b=2/16 3/4B/ (5)a/aB/-=3/16 114aa 14b/b (6)aabb=1/16
Incomplete dominance in dihybrid crosses • One gene with partial dominance, one gene with complete dominance: F2 = 3:6:3:1:2:1 3/4 B/- (1) A/A B/- = 3/16 1/4 A/A 1/4 b/b (2) A/A b/b = 1/16 3/4 B/- (3) A/a B/- = 6/16 1/2 A/a 1/4 b/b (4) A/a b/b = 2/16 3/4 B/- (5) a/a B/- = 3/16 1/4 a/a 1/4 b/b (6) a/a b/b = 1/16
Incomplete dominance in dihybrid crosses Two genes with partial dominance: F2=1: 2: 1: 2: 4: 2: 1: 2: 1 14B/B AA B/B 1/16 1/4AA 12B/b AaB/b 2/16 14b/b AA b/b 1/16 14B/B Ala b/B =2/16 1/2Aa 1/2B/b Aa b/b =4/16 114b/b Aa b/b =2/16 14B/B ∥aB/B =1/16 14a/a 12B/b ala b/b =2/16 14b/b a/a blb =1/16
Incomplete dominance in dihybrid crosses • Two genes with partial dominance: F2 = 1:2:1:2:4:2:1:2:1 1/4 B/B A/A B/B = 1/16 1/4 A/A 1/2 B/b A/A B/b = 2/16 1/4 b/b A/A b/b = 1/16 1/4 B/B A/a B/B = 2/16 1/2 A/a 1/2 B/b A/a B/b = 4/16 1/4 b/b A/a b/b = 2/16 1/4 B/B a/a B/B = 1/16 1/4 a/a 1/2 B/b a/a B/b = 2/16 1/4 b/b a/a b/b = 1/16
Dominance is a relationship between two alleles. Alleles show different degrees of dominance RR R2R2 Phenotype of parents Phenotype of RR2 offspring @@ ver- Incomplete dominance Over- dominance (RR intermediate between dominance (RR>RR) RR and R2R) (R1R2>R2R2) Dominance Dominance of r allele of r allele (RR= RR) (R1R2=R2R2)
• Dominance is a relationship between two alleles. • Alleles show different degrees of dominance. 4.2