1 Lecture #6 – Bombay Phenotype & Epistasis Wheeler High School The Center for Advanced Studies in Science, Math & TechnologyLecture #6 – Bombay Phenotype & EpistasisPost-AP DNA/Genetics – Ms. Kelavkar
2 The Bombay Phenotype Discovered in 1952 Woman from Bombay who was genetically blood type B but phenotypically OHomozygous for recessive mutation in gene known as FUT1Having this mutation meant she could not make any H substance
3 What type of mutation is this? Bombay Phenotype = Has the genes to makeandbut has a mutation in the gene that makes
5 Bombay Phenotype & Epistasis Many traits characterized by a distinct phenotype are affected by more than one geneEpistasis occurs when one gene masks the effect of another gene or when two gene pairs complement each other such that one dominant allele is required at each locus to express a certain phenotype.
6 Bombay Phenotype & Epistasis The Bombay phenotype for ABO blood groups is an example of epistasishomozygous recessive condition at one locus masks the expression of a second locusA locus is a position on a chromosomeIndividuals with the Bombay Phenotype have the genes to make the A or B antigen at one loci but lack the genes that produce the H substance produced at another loci.No H antigen gives you the O phenotype!
7 A ratio expressed in 16 parts (e. g A ratio expressed in 16 parts (e.g., 3:6:3:4) suggests that epistasis is occurring which means genes are ‘interacting’ to give a particular phenotype.
8 Epistasis in Mice B is the pigment gene! Agouti = A-Black = aaPigment = B-No pigment = bbAgouti = A-Black = aaPigment = B-No pigment = bbwt coat color in mice is called agouti (A-)Agouti is dominant to black (aa)When a recessive mutation, bb, at a separate locus is homozygous, all pigmentation is eliminated giving albino miceF1: AaBb x AaBbF2 RatioGenotypePhenotypePhenotypic Ratios9/16A-B-Agouti9/16 agouti3/16A-bbAlbino4/16 albinoaaB-Black3/16 black1/16aabbalbino
10 Gene Interaction Diagram Epistasis in MiceMouse color is dependent on 2 different genes that interact (A- and B-)…Gene Interaction DiagramGene BGene AB-Black PigmentA-AgoutiSo there are 3 possibilitiesNo PigmentbbA-Albino MouseAgouti = A-Black = aaPigment = B-No pigment = bbB-Black PigmentaaBlack
11 Try One Out!! F1: Aabb x AaBb Agouti = A- Black = aa Pigment = B- No pigment = bbTry One Out!!F1: Aabb x AaBbF2 phenotypic proportionsF2 Aa x AaF2 bb x Bb½ B-3/8 A-B- (Agouti)¾ A-½ bb3/8 A-bb (Albino)1/8 aaB- (Black)½ B-¼ aa1/8 aabb (Albino)½ bb
12 Lethal MutationsA loss of function mutation can sometimes be tolerated in the heterozygous state but may behave as a recessive lethal allele in the homozygous state, in which case homozygous recessive individuals will not survive.This is a lethal mutation!
13 Inheritance patterns in 3 crosses involving the normal wt agouti allele (A) and the mutant yellow (AY) allele in the mouse. Note that the mutant allele behaves dominantly to the normal allele in controlling coat color, but it also behaves as a homozygous recessive lethal allele. The genotype AYAY does not exist.
14 Any Questions?I am an Agouti mouseI’m an AlbinoI’m a Black mouse