Chapter 6 notes
What are the different kinds of gene interactions?
Complete dominance and receissiveness
In PKU wt allele is dominant and the mutant is recessive that effects the gene encoding the enzyme PAH
that breaks down the phenylalanine entering the blood stream leading to accumulation of Phe.
However, the presence of heterozygote results in no PKU because the PAH gene is haplosufficient.
Null mutation would lead to an inadequate amount concentration of an enzyme or protein in
heterozygote form. This leads to conditions like defects in the development if pharyngeal arteries in
mice with haploinsufficine tTbx1 gene.
Polypeptides with this mutation act as spoilers and it binds to the wt polypeptide and distorts it or
interferes with the function—this occurs with homodimeric and heterodimeric proteins. When the gene
product is a monomer the mutant binds to the substrate leaving very little to bind with the wildtype.
Example: brittle bone disrase osteogenesis imperfecta.
The phenotype of the heterozygote is intermediate between those of the two homozygotes on some
quantitative scale of measurement. Example four o’clock plants 1:2:1 of red:pink:white.
The expression of both alleles of a heterozygote eg. ABO blood where the alleles determines the
presence and form of a complex sugar molecule present on the surface of RBCs.
Sickle cell an