Complementation test

In this presentation, I'll try to explain the complementation test. This test is important for assessment of functional allelism.

1. Complementation test
Presented by:
Sanjay Kr. Vishwakarma

2. Complementation test
•Different mutations that affect a characteristic occur at the
same locus (are allelic) or at different loci
•Edward Lewis developed the complementation test for
functional allelism

3. •A double heterozygote, which carries two mutations and their
wild-type alleles, that is, m1 and m1
+
along with m2 and m2
+
,
can exist in either of two arrangements
•Two mutations are on the same chromosome, the
arrangement is called the coupling or cis configuration, and a
heterozygote with this genotype is called a cis heterozygote
•Two mutations are on different chromosomes, the
arrangement is called the repulsion or trans configuration

4. •Organisms contain the same genetic markers, but in different arrangements have
different phenotypes i.e., position effects
•The type of position effect that Lewis observed is called a cis-trans position
effect
•Lewis’ discovery of cis-trans position effects led to the development of the
complementation test or trans test for functional allelism

5. •This test allows geneticists to determine whether mutations that
produce the same or similar phenotypes are in the same gene or in
different genes
•Lewis observed that fruit flies carrying certain mutants in the cis
and trans configurations had different phenotypes
•Flies that are homozygous for the X-linked mutations apr and w
have apricot-colored eyes and white eyes, respectively, in contrast
to the red eyes of wild-type Drosophila

6. •When Lewis produced cisheterozygotes with the genotype apr
w/apr
+
w
+
, they had red eyes just like wild type flies

7. •When he constructed trans heterozygotes with genotype apr
w
+
/apr
+
w they had light apricot-colored eyes

8. •If trans heterozygote has the mutant phenotype, then the two
mutations are in the same unit of function, the same gene
•Two mutations present in a trans heterozygote are both in the
same gene, both chromosomes will carry defective copies of
that gene
•Trans heterozygote will contain only nonfunctional products of
the gene involved and will have a mutant phenotype

9. •If the trans heterozygote has the wild-type phenotype, then
the two mutations are in two different units of function, two
different genes
•Trans heterozygote has the wild-type phenotype, the two
mutations are said to exhibit complementation or to
complement each other and are located in different genes
•Trans heterozygote will contain functional products of both
genes and, therefore, will exhibit the wild-type phenotype

10. Multiple Choice Question

11. 1)Inordertodetermineifmutationsfromdifferentorganismsthatexhibitthesamephenotype
areallelic,whichtestwouldyouperform?
a)Testcross
b)Epistasistest
c)Complementationtest
d)Biochemicaltest
Answer:c

12. 2)Amutantscreenreveals4recessivemutationsforhairlessness–h1,h2,h3,andh4–in
laboratorymice.Aseriesofcomplementationtestsshowedthefollowingresults:h1andh2fail
tocomplement;h1andh3complement;h2andh3complement;h2andh4failtocomplement.
Theseresultsshowthatthemutationsoccurat
a)Onegene
b)Twogenes
c)Threegenes
d)Fourgenes
Answer:b

13. Thank You