What Is Dominance in Genetics Definition Types and Examples
In this article, we will define dominance and understand the concept of dominance in detail. The term dominance is used in the field of Genetics. Genetics is the branch of science that deals with the study of inheritance and variation among the characters. Variation is the reason for the difference of characters among the parents and offspring's. Dominance is used in genetics when two or more than two genes are in contact with one another and the gene that shows its expression is termed as a gene of dominance. This is the dominant meaning in biology. Here, in the next paragraph, we will study the principles of inheritance and variation and who gave this concept of what is dominant in biology and dominant trait meaning.
Concept of Dominance
Gregor Johann Mendel was the first scientist to give a scientific explanation about inheritance and variation. He did so by conducting hybridization experiments. He was the first to give the scientific explanation but he was not the first one to conduct these experiments. He modified the experiments in his way by considering two to three genes at a time in his experiment. This turned out to be the secret of his success. Knight and Goss first conducted these hybridization experiments. Mendel made changes according to his needs in the experiments and they turned out to be great for his studies. Dominant trait meaning is that when one gene of an allele masks or hides the function of another gene of the different allele. One is known as the dominant allele and the other is known as the recessive allele. A dominant trait example is the gene of height in pea plants. The tall gene expresses itself and masks the effect of the dwarf gene. This is a small idea of how we define dominance. Further, we will learn about the experiments of Mendel and the theories he published. This will help us understand dominant traits meaning more closely and dominant examples.
Mendel’s Laws of Inheritance
As we studied above, it was George Mendel who conducted experiments related to inheritance and variation of characters. He worked on the Pea plant or Garden Pea. He proposed the law of inheritance in living organisms. A character is a feature of an individual whereas a trait is a distinguishable feature of a character and its detectable variant. Tallness or dwarfness is an example of this trait. Mendel selected the pea plant because it had many distinct alternative traits. It also produces a large number of seeds. It completes its life cycle in one season. The flowers of the pea plant are true-breeding. This means that they show self-pollination. In pea plant, cross-pollination is also very easy. This cross-pollination also produces fertile hybrids. Mendel selected 14 pea plant varieties and 7 characters in the pea plant for carrying out his hybridization experiments. The seven characters were:
Seed shape
Seed colour
Flower colour
Pod colour
Pod shape
Stem height
Flower position
Dominant and Recessive
Based on his results and the results he obtained in the F1 generation. It was proposed by Mendel that when two dissimilar characters are present in an individual, only one of these characters can express itself in the next generation and another one is not able to express it. The characters that are expressed in the next generation are known as dominant characters and the characters that are not expressed in the next generation are known as recessive characters. We can also state that the allele that is dominant, masks or influences the characters of the recessive allele and stops it from expressing itself. Genotype is known as the genetic characters and phenotype is known as the physical characteristics that can be seen with the naked eye. This is how we define dominance and recessive traits.
[Image will be Uploaded Soon]
Mendel’s Laws
Based on his studies and the results he got after his experiments, he formulated 2 laws. They were known as Mendel’s laws of inheritance later. The first law or Law of Dominance and the second law or the Law of Segregation.
Law of Dominance:
As we know, Mendel gave this law by working on seven characters of the garden pea. He was able to find out that each of the characters is controlled by some discrete units. These discrete units were known as factors. These factors always occur in pairs. When two dissimilar types of factors are present then one factor expresses itself and the other factor is not able to express itself. The factor that expresses itself is known as the dominant factor and the other factor is known as the recessive factor. This law is not universally applicable.
Law of Segregation:
When two factors of a character are present in an individual, they are not mixed and they are both recovered as they are in the next generation. This can be seen when at the time of gamete formation that a gamete only carries one factor of a character. This law helps in ensuring the purity of gametes. This law is applicable in all conditions hence it is a universally accepted law.
Reasons for Mendel’s Success
As we read above about the work of Mendel on how he made run some hybridization experiments and on how these results or his theories are correct in today’s world also. The reasons for the success of Mendel were:
Mendel was a Mathematician. He applied his knowledge of mathematics and statistics to his experiments. These served as good logic in analysing his results.
The main reason was he used to keep records of his experiments. He gave all the details of the number and the type of individuals. These are a necessity in genetic studies.
He experimented with the pea plant and obtained hundreds of offspring. The large size of his samples gave credibility to his experiment. In large sample sizes, the chances of error are very little.
He also tried to formulate theoretical explanations in his observed results. They were further tested by conducting experiments for the successive generations of the test plants. This helped in making rules of inheritance rather than making unsustained ideas.
FAQs on Dominance in Genetics and Inheritance Patterns
1. What is dominance in genetics?
Dominance in genetics is the phenomenon where one allele masks or suppresses the expression of another allele in a heterozygous condition. In simple terms, when two different alleles are present for a trait, the dominant allele determines the observable characteristic (phenotype), while the recessive allele remains unexpressed.
- Occurs in heterozygous genotypes (e.g., Aa).
- The dominant allele is represented by a capital letter (A).
- The recessive allele is represented by a lowercase letter (a).
2. What is the difference between dominant and recessive alleles?
The key difference is that a dominant allele expresses its trait even in the presence of another allele, while a recessive allele expresses only when two copies are present. Dominant traits appear in both homozygous dominant (AA) and heterozygous (Aa) conditions, whereas recessive traits appear only in homozygous recessive (aa).
- Dominant allele: Expressed in AA and Aa.
- Recessive allele: Expressed only in aa.
- Dominance affects phenotype, not necessarily allele frequency.
3. How does dominance work in Mendelian inheritance?
In Mendelian inheritance, dominance works by allowing one allele to determine the phenotype in a heterozygous pair. During fertilization, offspring inherit one allele from each parent, and if one allele is dominant, it masks the recessive allele.
- Step 1: Each parent contributes one allele via gametes.
- Step 2: Alleles combine to form a genotype (e.g., Aa).
- Step 3: The dominant allele determines the visible trait.
4. What is an example of dominance in humans?
An example of dominance in humans is Huntington’s disease, which is caused by a dominant allele. A person with just one copy of the mutant allele (Hh) will develop the disorder.
- Genotype HH or Hh → disease present.
- Genotype hh → normal.
- This is an example of an autosomal dominant trait.
5. What is complete dominance?
Complete dominance occurs when the dominant allele completely masks the effect of the recessive allele in a heterozygote. The heterozygous phenotype is identical to the homozygous dominant phenotype.
- Example: Mendel’s pea plants with purple (P) and white (p) flowers.
- PP and Pp → purple flowers.
- pp → white flowers.
6. What is incomplete dominance?
Incomplete dominance is a pattern of inheritance in which the heterozygous phenotype is intermediate between the two homozygous phenotypes. Neither allele completely masks the other.
- Example: Red (RR) × White (WW) flowers.
- RW → pink flowers.
- Shows blending of traits.
7. What is codominance in genetics?
Codominance is a genetic condition in which both alleles in a heterozygote are fully and equally expressed. Neither allele masks the other.
- Example: AB blood group in humans.
- Genotype IAIB produces both A and B antigens.
- Both traits appear simultaneously.
8. Does dominance mean an allele is more common?
Dominance does not mean an allele is more common in a population; it only refers to how a trait is expressed in a heterozygote. An allele can be dominant but rare, or recessive but common.
- Example: Polydactyly is dominant but rare.
- Allele frequency depends on evolutionary factors.
- Dominance affects phenotype, not population prevalence.
9. How is dominance determined at the molecular level?
Dominance at the molecular level is often determined by whether one allele produces a functional protein while the other does not. The functional allele usually masks the effect of the nonfunctional allele.
- Dominant allele → produces sufficient functional protein.
- Recessive allele → may produce no or defective protein.
- Protein activity determines the phenotype.
10. What is the difference between homozygous and heterozygous in relation to dominance?
Homozygous individuals have two identical alleles, while heterozygous individuals have two different alleles, which determines how dominance is expressed. Dominance is observed only in heterozygous conditions.
- Homozygous dominant (AA) → dominant trait.
- Homozygous recessive (aa) → recessive trait.
- Heterozygous (Aa) → dominant trait expressed if complete dominance occurs.
