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Each chromosome has one DNA molecule Each chromosome has many genes
Lecture 10: What is a gene? Each chromosome has one DNA molecule Each chromosome has many genes A gene produces a protein that give rise to a phenotype A gene has many forms- alleles Different alleles are caused by different changes in the same gene Mutations in different genes CAN give you the same phenotype chromosome yellow Blanco eye Shaven body Forked bristle White eye Many genes Genes on DNA w1 w2 w3 Mutations in white b1 b2 Mutations in blanco
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Complementation Glutamic acid-
The complementation test is a rapid method of determining whether two independently isolated mutants with the same phenotype (in the same pathway) are in one or two (or more) genes. Ornithine Citruline Arginine Enzyme1 Enzyme2 Glutamic acid- Both mutant1 and mutant2 cannot make arginine. If you did not know the pathway you would wonder if these two mutants were mutations in the same gene or mutations in two different genes If you are working with Neurospora, you can feed the intermediate (Citruline) to the mutants and see if they can now make arginine. You are “complementing” the mutants with chemical intermediates Mutant1+ citruline=cell makes arginine Mutant2+citruline=cell cant make arginine- mutant
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B----> E----> A----> N
This process might also identify multiple mutants for the steps in the pathway! B----> E----> A----> N Mut3 Mut1 mut4 Mut2 mut1 and mut4 might be two different mutations in the same gene. OR Mutations in two different genes that work in the same pathway B----> E----> S--- A----> N Mut3 Mut1 Mut2 mut4 Feeding intermediates to complement genetic mutations is not possible all the time. The wildtype eye color in flies is red Say two different laboratories isolated mutants that had white eyes. You cant feed flies eye pigment precursor to figure things out!
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White and Blanco-one or two genes?
QUESTION Are the two independently isolated mutations THAT HAVE THE SAME WHITE EYE PHENOTYPE disrupting the same or different genes? Precursor (white) Product (red pigment) Enzyme1 Gene1 Blanco=White???? OR Precursor (white) Intermediate (white) Product (red pigment) Enzyme1 Enzyme2 Gene1 White Gene2 Blanco
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Easy way!!! There is an easier way
QUESTION: IS BLANCO THE SAME GENE AS WHITE or IS BLANCO AND WHITE TWO DIFFERENT GENES The following cross is performed: True breeding Blanco x true breeding white
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Cross White Blanco Female male w/w x b/b The actual Cross
white (w) x blanco (b) White Blanco Female male w/w x b/b
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If White and Blanco are the same gene ….
Precursor (white) Product (red pigment) Enzyme1 White= Blanco wwww x wbwb (white eye) (white blanco eye) F1 wwwb Phenotype= ????? In the F1 will the flies be red eyed or white eyed? All white
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What is the eye-color of the w/b fly?
The cross WHITE EYE What are genotypes and phenotypes of the cross ww x bb F1 b w w b (?) What is the eye-color of the w/b fly? ?White or Red???? ww wb
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One gene w wb ww wb bb Precursor -------> product White enzyme1 red
White x white wb wb F1 wb White What happens if you do a self cross with the F1 w ww (white) b wb (white) F2 wb (white) bb (white) b
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If White and Blanco are two genes……
Precursor (white) Intermediate (blanco) Product (red pigment) Enzyme1 Enzyme2 Gene1 White Gene2 Blanco wwBB x WWbb (white eye) (blanco eye) F1 Ww Bb phenotype= ????? In the F1 what percentage of flies would be red eyed and what percentage would be white eyed? All red
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(white eye) (blanco eye)
wwwwBB x WWbb (white eye) (blanco eye) F1 Www Bb phenotype= RED In the F1 what percentage of flies would be red eyed and what percentage would be white eyed? All red ww B W bb
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Gene interactions give 9:7
Precursor----> intermediate----> product white white red EnzW EnzB White x white wwBB WWbb F1 WwBb (phenotype= red) What happens if you do a self cross with the F1 WB Wb wB wb WWBB WWBb WwBB WwBb WWbB WwbB wWBB wWbB wWBb 9 W-B- red 3W-bb white 3wwB- white 1wwbb white WWbb Wwbb wwBB wwBb wWbb wwbB wwbb F2
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Map Genes Mapping genes takes lots of crosses and is time consuming
You could map each mutation. If Blanco = white then the two mutations WILL map to the same spot on the chromosome. That would indicate that they are the SAME GENE -two different alleles! yellow singed Shaven body forked white blanco If on the other hand the two mutations map to different regions of the chromosome (or different chromosomes) then that would indicate that they are two different genes. yellow singed Shaven body forked white Blanco Mapping genes takes lots of crosses and is time consuming There is an easier way!
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How many genes? The answer to the question (What is the eye-color of the w/b fly?) depends on whether the w and b mutations disrupt the same gene or two different genes. What if the w and b mutations disrupt the same gene? w b w b F1 white=blanco If the F1 w/b flies are white-eyed, we know that the white and blanco mutations disrupt one gene. What if w and b mutations disrupt two genes? w B+ W+ b W+ b w B+ F1 If the F1 w/b flies are red-eyed, we know that the white and blanco mutations disrupt two genes.
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Single gene If the F1 flies are white-eyed, the mutations disrupt
the same gene. A geneticist would say the two mutations do not complement one another because normal function is not restored. If there is a single gene then yellow singed Shaven body forked white blanco If the researchers discover that blanco (b) and white (w) are mutations within the same gene, there is a problem. The same gene has two names. One would like to have names that indicate that these are two alleles of the same gene. These are renamed White becomes w1 Blanco becomes w2 or wb
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Two genes Precursor white Intermediate white Product red Enzyme1
If the F1 w/b females are red-eyed, then white and blanco mutations disrupt two genes. You say that these two mutations complement one another. They complement because normal function is restored There are two genes --- W and B. If there are two genes then: How do these two genes relate to one another (one gene one enzyme) Precursor white Intermediate white Product red Enzyme1 Enzyme2 gene1 gene2 white blanco w B+ W+ b yellow singed Shaven body forked white blanco
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Precursor white Intermediate Product red Enzyme1 Enzyme2 gene1 gene2 OR Precursor white Intermediate Product red Enzyme1 Enzyme2 gene2 gene1
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Complementation analysis
Genotype eye color complementation Ww1/Ww2 white - N Ww1/Bw3 red + Y Ww2/Bw3 red + Y w1, w2 = geneW= complementation groupW (multiple alleles) w3,= geneB= complementation groupB
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Suppose we isolate 5 delta wing mutations
We want to know how many genes are disrupted in these mutations and which mutations are in the same complementation group
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Complementation crosses
We systematically perform crosses First we perform the cross d1/d1 x d2/d2 F1 d1/d2 are produced wing= flat or delta If they are flat, they disrupt 2 genes Then we perform d1/d1 x d3/d3 F1 d1/d3 wing=flat or delta You construct a complementation table
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Complementation crosses
You construct a complementation table + is flat wing - is delta wing Mutation complement mutation don’t complement Different genes same gene (diff complementation grp) (same complementation grp) d1 d2 d3 d4 d5 d d d d d Complementation Grp1= Gene1= alleles (d1, d2, d5) Complementation Grp2 Gene2= alleles (d3, d4)
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