Question

Which one shows complementary gene interaction ratio 9 : 7?
A. Four O’clock plant
B. Feather color in Fowl
C. Flower color in Sweat Pea
D. Fruit shape in Shepherd’s purse
E. Coat color in Mouse

Answer 1

Gene is a sequence of nucleotides present in the DNA or RNA. It is responsible for encoding a gene product in the form of RNA or protein. The pairs of genes in an organism are often found to represent functional interactions and this is referred to as gene interactions. They are very useful in determining the relationship between the genotype and phenotype of an organism.

Complete answer:
The complementation of genes is an interaction between two dominant non-inter allelic genes in which each gene holds its own characteristic but develops a new trait. Complementation occurred between two non-allelic genes, these two genes go through a specific pathway, and their functional products are required for gene expression, then one receives an allelic pair and results in a new phenotype. These genes are called complementary genes. Complementary genes are the type of two genes that contribute and are characterized as single. Here both genes can mask the effect of the other. Complementary genes can be also defined as any instance in which dominant forms of both genes are required for the dominant characteristic to be seen
Different types of plants show different ratios in complementary gene interaction. In the case of a complementary gene, when two dominant genes come together to interact then Mendelian ratio 9:3:3:1 is changed to 9:7 due to the complementation of both genes.
The complementary gene interaction can be found in flower colour in sweat pea with the ratio of 9:7. A Four O’ clock plant shows incomplete dominance and its ratio is 1:2:1. In incomplete dominance, the dominant allele is unable to completely cover up the effects of the recessive alleles and the phenotype shows the blending of both the alleles.
Supplementary genes are a type of gene complementation when the interaction takes place in two different types of genes in which one type can express itself freely but other has no expression of its own. This type of interaction notice in feather colour in fowl and ratio is 9:3:4.
In the fruit shape in Shepherd’s purse, the type of gene complementation known as duplicate genes occurs when two or more genes either individually or in combination produce the same phenotypic effect. The ratio of this interaction is 15:1.
Coat colour in mice shows lethal genes. Lethal genes are considered as the factors when it replaces the normal allelomorphs to bring about abrupt changes and causes severe physiological changes ultimately leading to death of the organism. In this type of interaction 2:1 ratio can be observed.

Therefore, the correct and appropriate option is option C.

Note: When two dominant non-inter allelic genes interact with each other and form a new trait then it is called complementation of gene. For the production of a dominant character trait, both the genes to be present necessarily. In a complementary gene interaction ratio is 9:7 and flower colour in sweat pea shows this type of gene interaction.