Incomplete Dominance Vs Co-Dominance Overview

Incomplete dominance definition

When the dominant allele does not completely suppress the expression of the recessive allele’s phenotype, incomplete dominance develops, giving rise to an intermediate phenotype in the heterozygote.

• Due to the phenotype’s mixture of dominant and recessive genes, incomplete dominance is also known as partial dominance or semi-dominance.
• Flowers provide an illustration of this, where the recessive allele is white, and the dominant allele is red. However, because of partial dominance, the heterozygous flowers from these alleles may look pink.
• In cases of partial dominance, the dominant allele is unable to entirely suppress the recessive gene; consequently, the phenotype is a mixture of both.
• It is significant that incomplete dominance exists, since it explains why Mendel’s experiment failed to identify a combination of two alleles.
• According to Mendel’s explanation of the Law of Domination, one of the two alleles is dominant because it always outweighs the recessive one.
• Since the pea plant he chose for his experiment didn’t exhibit imperfect dominance, Mendel was unable to analyse it.
• His approach may still be used to predict the outcomes of incomplete dominant allele crossings, though. His model predicts that the ensuing F1 generation will have a phenotypic ratio of red: pink: white and a genotypic ratio of 1:2:1.
• This finding suggests that, even in the presence of partial dominance, Mendel’s rule still governs the inheritance of alleles.
• There is no dominance in quantitative genetics if the phenotype of heterozygous alleles falls perfectly between (numerically) that of the two homozygotes. For dominance to develop, the phenotype of the heterozygote has to be closer to one of the homozygotes.

Co-dominance definition

• Co-dominance occurs when two alleles of a gene in a heterozygote miss the dominant and recessive link, and every allele has the potential for phenotypic expression to a certain degree.
• Because the heterozygote displays the traits of both homozygotes, co-dominance is frequently seen as having no dominance at all.
• In contrast to any of the homozygous genotypes, the heterozygote genotype results in a phenotype.
• All upper case base symbols with various superscripts are utilised for codominant alleles. The capital letters signify that even in the presence of an alternative allele, each allele may still partially express itself.
• Co-dominance could be observed in plants when the dominant phenotype is red and the recessive phenotype is white. The heterozygote’s flowers will feature pink and white spots.
• Mendel did not explain co-dominance since the model he used did not express it, similar to incomplete dominance.
• His approach may still be used to predict the outcomes of allele crossings via co-complete dominance, though. His model predicts that the ensuing F1 generation will have a red: spotted: white phenotypic ratio and a genotypic ratio of 1:2:1.
• Co-dominance can sometimes be seen in less obvious qualities like the blood type, but it is typically easy to spot in plants and animals with two distinct hues.
• Co-dominance differs from incomplete dominance because the two alleles co-exist in co-dominance but independently, whereas in imperfect dominance, the phenotype is a combination of the two alleles.

Examples of incomplete dominance

Humans have wavy hair.

• Humans with straight hair have a recessive tendency, whereas those with curly hair have the dominant trait.
• The resultant phenotype in heterozygous species is wavy hair, which falls somewhere between straight and curly.
• Therefore, partial dominance causes wavy hair because the two features are mixed together to produce the phenotype.
• Thus, wavy hair is a unique phenotype that is distinct from straight or curly hair.
• When two parents have homozygous genotypes, their offspring will have the phenotypic ratio of curly: wavy: straight, or a genotypic ratio of 1:2:1.

Pink flowers in Mirabilis jalapa

• Once a homozygous or pure line with red petals (C1C1) is combined with a pure line with white petals (C2C2), the F1 offspring lacks red petals but has pink petals. This is another example of incomplete dominance (C1C2).
• If an F2 is created, its descendants show the following traits:

¼ red petals – 1 C1C1

½ pink petals – 2 C1C2

¼ white petals – 1 C2C2

• Red and white are the dominant and recessive traits for the colour of the flowers, respectively. As a result, pink is the phenotypic of partial dominance.
• The trait that results from this process is new and wasn’t present in the progeny of homozygous parents.

Examples of co-dominance

• Blood type in humans
• The genes for the proteins that are found on the exterior of blood cells in humans are used to identify blood types.
• The three alleles that are present are A, B, and O. A and B stand for two distinct proteins, but O denotes the absence of all proteins.
• Because of co-dominance, A and B proteins may co-exist, much like two hues in a flower.
• As a result, the children may have the blood type AB if both the proteins A and B are passed down to them and are expressed.
• The blood type O, however, illustrates a dominant/recessive connection in which O is not produced if the A and B genes are active.

Livestock

• Because of co-dominance, several animals have unique skin and feather hues.
• While a chicken having white feathers breeds with a chicken having black feathers, the offspring will contain both white and black feathers because of co-dominance.
• Both qualities express themselves independently of one another during co-dominance.
• Similar behaviour is seen in cows, where crossing black and white cows produces offspring with white and black spots.
• Co-dominance causes both features to manifest independently of one another.
• The mixed coat of hair in cattle that is diverse in colour is known as roan, and it is also a product of co-dominance.

References and Sources

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