LIFESCI 4 Lecture Notes - Lecture 3: Genotype, Phenotype, Allele
Incomplete/partial dominance
• Phenotype of heterozygous hybrid is intermediate between homozygous parents
- Phenotypic ratios are same as genotypic ratios
• red (homo), white (homo), pink flowers (hetero)
• Genotype ratio = phenotype ratio (red : pink : white) = 1:2:1
• Mendel s laws are still valid at the genotypic level
• Gene turns precursor molecule into red pigment
- Individual with 2 copies of A -> makes 2x red pigment from precursor
- Individual with Aa has 1 allele making the pigment, the other does’t -> make 1x
pigment (not as red)
- Individual with aa alleles cannot make functional protein -> does’t ake red
pigment -> white
Co-Dominant Alleles
• phenotypes of both alleles are observed in the heterozygotes
- F1 hybrids express phenotype of both parents equally
- Phenotypic ratios are same as genotypic ratios
• hemogglutination assay
find more resources at oneclass.com
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• L gene encodes a protein that puts surface antigen on blood cells
- blood type M has only M antigens on the surface
- blood type N has only N antigens on the surface
- heterozygous blood type has both M and N antigens on the surface
• antibodies/antiserum that strictly direct against only M or N
- serum causes blood cells to clump together
- anti-M serum causes M blood to clump, not N; vice versa
- both anti-M and anti-N serum cause glutination of MN blood
• M and N are co-dominant
Multiple alleles
ABO blood group
• Multiple alleles and incomplete dominance
• 3 alleles: IA IB and i
- IA , IB co-dominant, i recessive
• multiple alleles controlling single gene vs multiple genes for same process
difference in F2 phenotypic ratios
- 1:2:1, 3:1, 2:1—single gene, multiple alleles
- 9:3:3:1 (or variation)—two genes
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Incomplete/partial dominance: phenotype of heterozygous hybrid is intermediate between homozygous parents. Individual with 2 copies of a -> makes 2x red pigment from precursor. Individual with aa has 1 allele making the pigment, the other does(cid:374)"t -> make 1x pigment (not as red) Individual with aa alleles cannot make functional protein -> does(cid:374)"t (cid:373)ake red pigment -> white. Co-dominant alleles: phenotypes of both alleles are observed in the heterozygotes. F1 hybrids express phenotype of both parents equally. Phenotypic ratios are same as genotypic ratios: hemogglutination assay, l gene encodes a protein that puts surface antigen on blood cells. Blood type m has only m antigens on the surface. Blood type n has only n antigens on the surface. Heterozygous blood type has both m and n antigens on the surface: antibodies/antiserum that strictly direct against only m or n serum causes blood cells to clump together. Anti-m serum causes m blood to clump, not n; vice versa.
