The document discusses complementation in genetics, where two strains with different homozygous recessive mutations can produce wild-type offspring if the mutations are in different genes. It also describes the complementation test, a method to determine if mutations are in the same or different genes, and introduces the concept of cis and trans configurations in heterozygotes. Additionally, examples from Drosophila melanogaster highlight how complementation can occur, allowing for the analysis of gene function.

1. PRESENTED BY- SOMASHREE DAS
REG NO- 15KUST4023
M.Sc 3rd SEM
DEPARTMENT OF BIOTECHNOLOGY
RAMAIAH COLLEGE OF ARTS, SCIENCE AND COMMERCE 1/12

2.  Complementation occurs when two strains of an organism with different
homozygous recessive mutations that produce the same mutant phenotype (for
example, a change in wing structure in flies) produce offspring with the wild-type
phenotype when mated or crossed.
 Complementation will occur only if the mutations are in different genes.
 In this case, each strain's genome supplies the wild-type allele to "complement"
the mutated allele of the other strain's genome. Since the mutations are recessive,
the offspring will display the wild-type phenotype.
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DEPARTMENT OF BIOTECHNOLOGY 2/12

3.  A complementation test (sometimes called a "cis-trans" test) can be used
to test whether the mutations in two strains are in different genes.
 Complementation will not occur if the mutations are in the same gene.
 The complementation test was developed by American geneticist Edward B.
Lewis.
 A heterozygote with two mutations of the same gene will produce only
mutant mRNAs, which result in mutant enzymes.
 The two mutations will complement each other and produce the wild-type.
 Mutations that fail to each other are termed as functional alleles.
 The test for defining alleles strictly on the basis of functionality is termed
the cis-trans complementation test.
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4.  Thus the two mutations will complement each other and produce the wild-type.
 Mutations that fail to complement each other are termed as functional alleles.
 The test for defining alleles strictly on this basis of functionality is termed as cis-
trans complementation test.
Source: DNA, it’s mutation, repair and damage; pg. no. 319; Genetics-Tamarin
RAMAIAH COLLEGE OF ARTS, SCIENCE AND COMMERCE
 DEPARTMENT OF BIOTECHNOLOGY 4/12

5.  A heterozygote of two recessive mutations can have either trans or cis
arrangement.
 In trans position, functional alleles produce a mutant phenotype.
 In cis position, functional alleles produce a wild-type phenotype.
 This difference in phenotype is called cis-trans position effect.
Source: DNA, it’s mutation, repair and damage; pg. no. 319; Genetics-Tamarin
RAMAIAH COLLEGE OF ARTS, SCIENCE AND COMMERCE
DEPARTMENT OF BIOTECHNOLOGY 5/12

6.  The complementation test is used to establish how many units of genes are
defined by a given test of mutations that express the same mutant phenotypes.
 In Benzer’s work with rII mutants, the non-permissive strain K12(lamda) was
infected with a pair of rII mutant phages.
 If the phages produce progeny, the two mutants are said to complement each
other, meaning that the two mutations must be in different genes that encode
different products.
 If no progeny phages are produced, the mutants are not complementary indicating
that mutations are in the same functional unit.
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DEPARTMENT OF BIOTECHNOLOGY 6/12

7. Source: Mutation; pg.no.407; Genetics-Peter.J.Russel
RAMAIAH COLLEGE OF ARTS, SCIENCE AND COMMERCE
DEPARTMENT OF BIOTECHNOLOGY 7/12

8.  Each rII mutant phage that co-infects the non-permissive E.coli strain K12(lamda)
carries one rII mutation, a configuration of mutations called the trans
configuration.
 When both the mutations are carried on same chromosome, the configuration is
called cis configuration of mutations.
 Benzer called the genetic unit of function revealed by the cis-trans test as cistron.
A cistron is the smallest segment of DNA that encodes a piece of RNA.
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DEPARTMENT OF BIOTECHNOLOGY 8/12

9.  Example of complementation in a diploid organism :-
 Two true-breeding mutant strains of Drosophila melanogaster have black body
color instead of wild-type grey-yellow.
 When the two strains are crossed, all the F1 flies have wild-type body color.
 This is because complementation has occurred between mutations intwo genes,
each of which is involved in the body color phenotype.
 That is a recessive autosomal gene, ebony(e), when homozygous, produces a black
body color.
 On another autosome a different recessive gene, black(b), also produces a black
body color when homozygous.
 Because the two parents are homozygotes, they are genotypically e/eb+/b+ and
e+/e+b/b, which is equivalent to trans configuration.
 The F1 have wild-type body color because complementation has occurred.
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DEPARTMENT OF BIOTECHNOLOGY 9/12

10. Source: Mutation; pg.no. 408; Genetics-Peter.J.Russel
RAMAIAH COLLEGE OF ARTS, SCIENCE AND COMMERCE
DEPARTMENT OF BIOTECHNOLOGY 10/12

11.  The number of units of functions (genes) is determined by complementation tests.
 Given a set of mutations expressing the same mutant phenotype, two mutants are
combined and the phenotype is determined.
 If the phenotype is wild-type, the two mutations have complemented and must be
in different units of function.
 If the phenotype is mutant, the two mutations have not complemented and must
be in the same unit of function.
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DEPARTMENT OF BIOTECHNOLOGY 11/12

12.  Genetics- Peter. J. Russel
 Genetics- Tamarin
 www.wikipedia.org
 www.britanica.com
 THANK YOU…………..
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DEPARTMENT OF BIOTECHNOLOGY 12/12