《遗传学》课程教学资源（PPT课件，英文版）Extensions of Mendelian Analysis

Extensions of Mendelian Analysis Interactions between alleles of one gene. Multiple alleles, incomplete dominance, codominance Interactions between alleles of two genes New phenotypes, epistasis Relationship between genotype phenotype lethals, variable penetrance, conditional alleles

Extensions of Mendelian Analysis • Interactions between alleles of one gene. • Multiple alleles, incomplete dominance, codominance • Interactions between alleles of two genes. • New phenotypes, epistasis • Relationship between genotype & phenotype • lethals, variable penetrance, conditional alleles

Interactions between alleles of one gene Dominance is a relationship between two alleles of the same gene. Several relationships are possible: complete dominance partial dominance incomplete dominance codominance overdominance Each relationship has particular characteristics

Interactions between alleles of one gene • Dominance is a relationship between two alleles of the same gene. • Several relationships are possible: • complete dominance • partial dominance/ incomplete dominance • codominance • overdominance • Each relationship has particular characteristics

Dominance is relative: an allele can be dominant to one allele and recessive to a third allele w/wa= red eye wa is recessive) w/ w1= red eye(w1 is recessive) wa/w1=light orange(wa is partially dominant to w1) The white gene has many different alleles, each producing a different amount of pigment: eosin, apricot, buff, etc

• Dominance is relative: an allele can be dominant to one allele and recessive to a third allele. w+ / wa = red eye (wa is recessive) w+ / w1 = red eye (w1 is recessive) wa / w1 = light orange (wa is partially dominant to w1 ). The white gene has many different alleles, each producing a different amount of pigment: eosin, apricot, buff, etc

agouti agout agouti AA agouti x black backlycllow bolly agouti AA Aa gout black gouti AA black backryellow belly x black black back/yellow belly a Dominance series: A> al>a

L Phenotype of first parent L Phenotype of second parent Type of dominance AIA A2/A2 A' / A2hybrids Complete A is dominant to A2 A2 is recessive to a A is dominant to aT Complete A' is recessive to a' Aand A are incompletely Incomplete dominant relative to each other and A2 are codominant Codominant relative to each other

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