Complementary genes: Definition, Meaning Types, Examples, Causes, Explanation

Complementary genes are a type of gene interaction in which two genes interact with each other, producing a specific phenotype or observable trait. The term complementary refers to the relationship that exists between the two genes that make up the phenotype. These genes, therefore, work together to complete an apparent result.

This Story also Contains

1. What are Complementary Genes?
2. Basic Concepts of Genetics
3. Gene Interaction
4. Complementary Genes
5. Examples of Complementary Genes
6. Recommended video for "Complementary Genes"
7. MCQs on Complementary Genes

A non-Mendelian gene interaction is an example of complementary genes. The inheritance pattern of these genes is a little complicated, as such gene interaction needs more than one gene for a specific trait. Examples include the flower colour in sweet pea plants. This indicates the mechanisms that the colour is determined by two genes interacting to complete the pathway and result in a specific flower colour. Complementary genes are an important topic in the biology subject.

What are Complementary Genes?

Complementary genes are genes that are similar in function and responsible for the expression of a specific phenotype. Dominant alleles in either gene of the pair are necessary to produce the trait; however, the trait can be masked if a recessive allele is present in the individual’s genotype. This concept is useful in genetics and heredity systems as it is necessary for understanding how some characteristics are inherited, and also the roles of genes and diverse phenotypes. This article will define complementary genes, explain their roles in genetic inheritance processes and give an insight to other related uses.

Basic Concepts of Genetics

Genetics is the branch of biology that deals with inheritance and variation in living beings. The genetics related to this topic involve the basics of:

Genes and Alleles

They are segments of DNA that contain information relating to protein synthesis or RNA molecules that are important for different activities in living organisms. Alleles are different forms of a given gene due to different types of mutation occurring in the gene locus. For instance, the genes governing eye colour could have several alleles, blue alleles or brown alleles.

Dominant and Recessive Traits

Expressed traits are those that result when any dominant allele is present in the genotype, irrespective of the presence of the other alleles. Such alleles and hence such traits are those that are expressed only where the individual inherited two alleles and both are of the recessive category. For instance, the brown-eyed allele is dominant over the blue-eyed allele, and unless they inherit two recessive alleles, they are blue-eyed.

Gene Interaction

Gene interaction can be defined as the phenomenon whereby the action of one gene depends on what alleles of one or many other genes are present. This interaction modifies the expression of traits in a manner that cannot simply be conferred by the direct results of either gene, making it a relatively complex task in genetics.

Types of Gene Interaction

Gene interaction can be classified as:

Epistasis

It can affect the function of another gene or hide its abnormalities. For instance, in Labrador retrievers, pigment deposition is dictated by the E gene, while the contributing factor in colour (either black or brown) is the B gene. It was further found that the recessive e allele at the E locus will be able to mask the effect of the B gene; thus, the dog will have a yellow coat despite the presence of the B allele.

Complementary Genes

That is, both genes will have to have a minimum of one dominant allele to exhibit a certain phenotypic feature. For instance, in sweet peas, the gene responsible for flower colour is controlled by the activity of two genes. The classification of the genotypes making up the flowers shows that only if both genes possess dominant alleles, then the flower is coloured; otherwise, the flower is white.

Duplicate Genes

A duplicate gene is when two genes are involved in a trait, and one of them has a dominant allele; the trait is displayed. This means that if one gene of each pair contains an A1 or a B1 allele, an organism will display the first manifestation of the trait.

Importance of Gene Interaction in Phenotypic Expression

Gene interactions hold a central position in providing an account for the phenomenon of multiple shape-regulatory genes. On this, they can help explain why traits do not always exhibit the basic Mendelian genetics and can offer an explanation of why there are differences in the variations of traits in diverse individuals and populations. Therefore, through such interactions, researchers can get estimates of the probable genetic results, originate the fundamental idea of genetic disorders, and investigate the progression of certain traits.

Complementary Genes

These are genes that cooperate in an organism to produce specific phenotypes. This is because two complementary genes are known to collectively bring about a certain characteristic of an organism. Only when there is at least one dominant allele for each gene will the given trait be expressed. Due to this rather stringent requirement, the participant gene is chosen carefully. This means that in a given population, for the absence of a particular trait, both genes must possess only recessive genes. This interaction shows how a simple phenotypic change can be controlled by several genes which all of which have equal efficacies.

Mechanism of Action

• In the case of complementary genes, the two genes work simultaneously in forming the whole phenotype.

• The alleles of both genes must be present, which makes the particular characteristic observable.

• If one gene has only recessive alleles, it does not allow the expression of the trait, no matter what alleles are present in the other gene.

• Example: In sweet peas, two genes control flower colours, which stand for colour P genes for pigment production. Both genes require a dominant allele for colouration in the flowers to be coloured, necessitating at least one dominant allele. If either of the genes is absent, that is, cc or pp, then the flowers will be white. This discussion portrays how the complementary genes cooperate and how their end product is developed with the final colour of flowers.

Examples of Complementary Genes

Complementary genes express themselves in a variety of phenotypes, such as flower colour, coat colour, etc. A few examples of complementary genes are:

Flower Colour In Sweet Peas

William Bateson and Reginald Punnett did experimental breeding on sweet peas, or Lathyrus odoratus. The investigators hybridised plants with two different fluorescent colours and had very young students describe the progeny.

Explanation of the Results: The allelic tests and interactions revealed that the quality of the colour and pigment of the sweet peas’ flowers depends on two genes: C and P.

For colour to show in the flower, the genotype of that particular flower should be PpCc Since C_P_ genes are incompletely dominant, one dominant allele is required for both genes to show colour.

If both are cc or pp, the flowers are white. While both genes are heterozygous dominant (Cc or Pp), the flowers are pink. This illustrated the situation where two distinct genes could only express this trait if they were both dominant.

Coat Colour in Mice

In mice, coat colour is controlled by pairs of complementary genes. Here, one gene, ‘A’ is responsible for synthesising pigment and gene ‘B’ is involved with the placement of the pigment.

Interaction and Phenotypic Expression: For a mouse to have the specific coat colour, there must be the presence of the dominant alleles in both of these genes (A_B_).

If either gene is homozygous recessive (aa or bb), the pigmentation process is said to be aborted, and there is said lack of the colour expected.

This outlines how alleles that are located on two different chromosomes work together to make coat colour contingency.

Other Examples in Plants and Animals

In corn, the colour of corn kernels can be determined by complementary genes is also a possibility. For instance, the alleles in two genes involved in the determination of pigment synthesis and its distribution produce different kernel colours if both are dominant.

In petunias, it is the complementary genes that control the flower colouration of the flowers. The combination of the genes relevant for colour production and colour development yields a palette of colours when both genes are homozygous. An individual possessing only recessive alleles, while a heterozygous individual, as defined by Griffiths, is one whose genotype includes at least one dominant allele.

The flowers will be white if at least one of these genes is recessive, as the hypothesis used in this cross appropriates the genes of dominant and recessive traits.

Recommended video for "Complementary Genes"

MCQs on Complementary Genes

Q1. Modified dihybrid ratio 9:7 observed by Bateson and Punette was found in

Option 1: Pisum sativum

Option 2: Cucurbita pepo

Option 3: Lathyrus odoratus

Option 4: Zea mays

Correct answer: (3) Lathyrus odoratus

Explanation:

In the Complementary factor -

1. In complementary gene interaction, two different genes work together to produce a specific phenotype, and both are required for the expression of the trait.

2. The 9:7 ratio arises because the presence of at least one dominant allele from both genes is necessary for the dominant phenotype; otherwise, the recessive phenotype is expressed.

3. This type of interaction was first observed by Bateson and Punnett in Lathyrus odoratus (sweet pea), demonstrating how two genes can complement each other's function.

Hence, the correct option is (3) Lathyrus odoratus

Q2. Which of the following best explains the relationship between complementary factor genes and the phenomenon of hybrid vigour?

Option 1: Complementary factor genes result in increased heterozygosity, which is responsible for hybrid vigour.

Option 2: Complementary factor genes result in increased homozygosity, which is responsible for hybrid vigour.

Option 3: Complementary factor genes are not related to the phenomenon of hybrid vigour.

Option 4: Complementary factor genes result in the production of sterile offspring, which is a characteristic of hybrid vigour.

Correct answer: (1) Complementary factor genes result in increased heterozygosity, which is responsible for hybrid vigour.

Explanation:

Hybrid vigour, also known as heterosis, is a phenomenon where the offspring of two different purebred varieties exhibit greater vigour and growth than either of the parent varieties. This phenomenon is often seen in crops and livestock. Complementary factor genes play a role in hybrid vigour by increasing heterozygosity. In a hybrid cross between two purebred lines, the complementary factor genes at different loci will contribute different sets of dominant and recessive alleles to the offspring. This results in greater genetic diversity and heterozygosity in the hybrid offspring, which can lead to increased growth and vigour. Hence, option A is the correct answer.

Hence, the correct answer is Option (1) Complementary factor genes result in increased heterozygosity, which is responsible for hybrid vigour.

Q3. Which of the following is an example of complementary factors?

Option 1: Albinism in humans

Option 2: Flower colour in sweet peas

Option 3: Seed colour in wheat

Option 4: Sickle cell anaemia in humans

Correct answer: (3) Seed colour in wheat.

Explanation:

In sweet peas, flower colour is controlled by two genes, A and B. The A gene produces an enzyme that converts a colourless precursor into a blue pigment, while the B gene produces an enzyme that converts the blue pigment into a red pigment. Both enzymes are required for the production of the red pigment, which gives the flower its normal colour. This means that the presence of both dominant alleles (AABB, AABb or AaBB) is required to produce a normal red flower. If either of the dominant alleles is absent (Aabb, aaBB or aabb), a mutant phenotype is produced. This is an example of complementary factors, where the expression of a trait is dependent on the presence of both dominant alleles at two different loci.

Hence, the correct answer is option (3) Seed colour in wheat.

Also Read:

• Practice MCQs on Complementary Genes

• Polygenic Inheritance

• Acquired And Inherited Traits