2. Gene interaction - complementary
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The document discusses complementary gene interaction, specifically in the context of flower color in Lathyrus odoratus (sweet pea). It explains that two non-allelic genes, referred to as genes c and p, are required to produce a purple flower phenotype; their presence results in a 9:7 phenotypic ratio of purple to white flowers in the F2 generation. The genes function together in the anthocyanin pigment synthesis pathway, and the absence of either gene leads to white flowers, illustrating the necessity of both genes for the expression of the purple color.
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GENE INTERACTION
A. COMPLEMENTARY GENE INTERACTION (9:7)
Ex: Flower color in Lathyrus odoratus (Sweet pea)
Complementation between two non-allelic genes (C and P) are essential for production
of a particular or special phenotype i.e., complementary factor.
Two genes involved in a specific pathway and their functional products are required
for gene expression, then one recessive allelic pair at either allelic pair would result in
the mutant phenotype.
When Dominant alleles are present together, they complement each other to yield
complementary factor resulting in a special phenotype.
They are called complementary genes.
When either of gene loci have homozygous recessive alleles (i.e., genotypes of ccPP,
ccPp, CCpp, Ccpp and ccpp), they produce identical phenotypes and change F2 ratio
to 9:7.
Example: Flower color in Lathyrus odoratus (Sweet pea)
In sweet pea (Lathyrus odoratus) two varieties of white flowering plants were seen.
Each variety bred true and produced white flowers in successive generations.
According to Bateson & Punnett, when two such white varieties of sweet pea were
crossed, the offspring were found to have purple-coloured flowers in F1.
But, in F2 generation 9 were purple and 7 white.
Anthocyanin pigment synthesis in sweet pea (Lathyrus Odoratus).
PATHWAY OF ANTHOCYANIN PIGMENT SYNTHESIS
The dominant allele or alleles [CC or Cc] of gene C are responsible for the presence of
chromogen, while the homozygous recessive [cc] alleles of this gene are responsible for
the absence of chromogen.
Likewise, the dominant alleles of gene P in homozygous [PP] or heterozygous [Pp]
conditions result in the production of an enzyme which is necessary for Anthocyanin
(Complementary factor) from chromogen, while homozygous recessive [pp] condition
does not produce any such enzyme.
Thus, only the double dominant genotype has both enzymes functional and can make
pigment.
Blocking either of two steps prevents pigment formation.](https://image.slidesharecdn.com/geneinteraction-complementary-210528091133/85/2-Gene-interaction-complementary-1-320.jpg)
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GENE INTERACTION
When a pure line variety of white flowered sweet pea was crossed with another pure
line variety of white flowered sweet pea, in F1 purple-colored flowered plants were
produced. The F1 plants when self- pollinated [crossed among themselves]; the
obtained F2 generation had the phenotypic ratio of 9 purple-colored and 7 white
flowered plants.
Pea Plant Variety : Variety-1 X Variety-2
Parental Phenotype : White-Colorless X White-Colorless
Sweet Pea flower Sweet Pea flower
Parental Genotype : ccPP X CCpp
Parental Gametes : cP X Cp](https://image.slidesharecdn.com/geneinteraction-complementary-210528091133/85/2-Gene-interaction-complementary-2-320.jpg)
2. Gene interaction - complementary
- 1. P a g e | 1 GENE INTERACTION A. COMPLEMENTARY GENE INTERACTION (9:7) Ex: Flower color in Lathyrus odoratus (Sweet pea) Complementation between two non-allelic genes (C and P) are essential for production of a particular or special phenotype i.e., complementary factor. Two genes involved in a specific pathway and their functional products are required for gene expression, then one recessive allelic pair at either allelic pair would result in the mutant phenotype. When Dominant alleles are present together, they complement each other to yield complementary factor resulting in a special phenotype. They are called complementary genes. When either of gene loci have homozygous recessive alleles (i.e., genotypes of ccPP, ccPp, CCpp, Ccpp and ccpp), they produce identical phenotypes and change F2 ratio to 9:7. Example: Flower color in Lathyrus odoratus (Sweet pea) In sweet pea (Lathyrus odoratus) two varieties of white flowering plants were seen. Each variety bred true and produced white flowers in successive generations. According to Bateson & Punnett, when two such white varieties of sweet pea were crossed, the offspring were found to have purple-coloured flowers in F1. But, in F2 generation 9 were purple and 7 white. Anthocyanin pigment synthesis in sweet pea (Lathyrus Odoratus). PATHWAY OF ANTHOCYANIN PIGMENT SYNTHESIS The dominant allele or alleles [CC or Cc] of gene C are responsible for the presence of chromogen, while the homozygous recessive [cc] alleles of this gene are responsible for the absence of chromogen. Likewise, the dominant alleles of gene P in homozygous [PP] or heterozygous [Pp] conditions result in the production of an enzyme which is necessary for Anthocyanin (Complementary factor) from chromogen, while homozygous recessive [pp] condition does not produce any such enzyme. Thus, only the double dominant genotype has both enzymes functional and can make pigment. Blocking either of two steps prevents pigment formation.
- 2. P a g e | 2 GENE INTERACTION When a pure line variety of white flowered sweet pea was crossed with another pure line variety of white flowered sweet pea, in F1 purple-colored flowered plants were produced. The F1 plants when self- pollinated [crossed among themselves]; the obtained F2 generation had the phenotypic ratio of 9 purple-colored and 7 white flowered plants. Pea Plant Variety : Variety-1 X Variety-2 Parental Phenotype : White-Colorless X White-Colorless Sweet Pea flower Sweet Pea flower Parental Genotype : ccPP X CCpp Parental Gametes : cP X Cp
- 3. P a g e | 3 GENE INTERACTION F1 Generation : CcPp Purple Colored F1 selfing: F1 X F1 : CcPp X CcPp Purple-colored Purple-colored F1 Gametes : CP Cp cP cp X CP Cp cP cp F2 generation : F2 phenotypic ratio = 9 Purple-colored : 7 White-colorless F2 Analysis: Genotype Flower color Enzyme Activities 9C_P_ Colored flowers: Anthocyanin produced Functional enzymes from both genes 3C_pp White flowers: No anthocyanin p enzyme nonfunctional 3cc P_ White flowers: No anthocyanin C enzyme nonfunctional 1ccpp White flowers: No anthocyanin c and p enzymes nonfunctional It is clear in the above example that for the production of the purple flower colour both complementary (C and P) genes are necessary to remain present. In the absence of either genes (C or P) the flowers are white. Thus, we can conclude that genes C and P interact and presence of both is essential for the purple colour in the flower. These types of genes in which one gene complements the action of the other gene, constitute complementary genes or factors. CP Cp cP Cp CP CCPP Purple colored CCPp Purple colored CcPP Purple colored CcPp Purple colored Cp CCPp Purple colored CCpp White Colorless CcPp Purple colored Ccpp White Colorless cP CcPP Purple colored CcPp Purple colored ccPP White Colorless ccPp White Colorless cp CcPp Purple colored Ccpp White Colorless ccPp White Colorless ccpp White Colorless