Question

Explain the terms incomplete dominance, codominance and multiple alleles. What is the result of differences in inheritance patterns of traits?

Short answer

Incomplete dominance is an inheritance pattern where the offspring's phenotype is an intermediate between its parents' phenotypes, like a red flower (RR) crossed with a white flower (WW) producing a pink offspring (RW). Codominance occurs when both alleles for a trait are expressed equally in the offspring, such as the AB blood type in humans. Multiple alleles refer to the presence of more than two possible alleles for a particular gene in a population, leading to greater genotypic and phenotypic variety, like the ABO blood group system. These differences in inheritance patterns contribute to genetic diversity and variation in traits, which is essential for the survival and adaptation of species.

Step-by-step solution

Introduction to Genetic Inheritance Patterns

Genetic inheritance patterns are how traits are passed down from parents to offspring through their genes. The way these traits are inherited depends on the interactions between the alleles of the genes that determine a particular trait. There are three important patterns of inheritance: incomplete dominance, codominance, and multiple alleles. In this exercise, we will define and provide examples of each, as well as discuss the results of differences in inheritance patterns.

Incomplete Dominance

Incomplete dominance is an inheritance pattern where the offspring's phenotype is an intermediate between its parents' phenotypes. This occurs when the dominant allele does not completely mask the recessive allele, resulting in a trait that is a blend of both alleles. For example, when a red flower (RR) is crossed with a white flower (WW), the offspring will have a pink color (RW), which is an intermediate between red and white. In this case, R represents the red color, and W represents the white color. The pink color appears because neither allele is fully dominant over the other.

Codominance

Codominance is another inheritance pattern where both alleles for a trait are expressed equally in the offspring. In this case, neither allele is recessive or dominant, and both are equally visible in the phenotype of the offspring. A common example of codominance is seen in the blood types of human beings. An individual inheriting an A allele from one parent and a B allele from another parent will have the AB blood type, in which both A and B antigens are expressed equally.

Multiple Alleles

Multiple alleles refer to the presence of more than two possible alleles for a particular gene in a population. This results in a greater variety of genotypes and phenotypes for a specific trait. The ABO blood group system is a prominent example of a gene controlled by multiple alleles, where three alleles (A, B, and O) dictate the possible blood types in humans. These blood types include A, B, AB, and O, each with their distinct antigens and antibodies.

Result of Differences in Inheritance Patterns

The differences in inheritance patterns lead to a diverse range of phenotypic outcomes in offspring, which contributes to the variation observed in populations. This genetic diversity is essential for the survival and adaptation of species, as it allows them to cope with changing environments and provides a wider range of traits that could be beneficial for maintaining the species. In summary, incomplete dominance, codominance, and multiple alleles all contribute to the variation in traits within a population, which is vital for the continued survival and evolution of that population.

Key concepts

Incomplete Dominance

Imagine you're mixing paints. If you blend red and white, you don't get red or white but pink, a mix of both. In the world of genetics, a similar phenomenon is known as incomplete dominance. This form of inheritance results in offspring with a phenotype that's a combination of its parents.

Take, for example, the classic case of flower color in snapdragons: when a red flower is crossed with a white flower, the result is not red or white offspring but pink flowers. In terms of genetics, if 'R' represents the red color allele and 'W' represents the white color allele, the pink flower has the genotype 'RW'.

Neither allele is dominant or recessive. This 'blending' effect creates a third phenotype that is not seen in the pure-breeding parents. More broadly, incomplete dominance shows us how genetic traits can mix, producing variety within a species beyond the classic dominant/recessive patterns.

Codominance

In a world where both partners in a dance shine equally, neither overpowering the other, you have a situation akin to codominance in genetics. It is a scenario where two different alleles for a genetic trait are both fully expressed, and neither one is overshadowed by the other. An individual with codominant alleles will exhibit characteristics of both.

Such a genetic partnership can be observed in human blood types. If a person inherits the 'A' allele from one parent and the 'B' allele from another, their blood type will be 'AB'. Both the A and B antigens will be present and visible in the phenotype - meaning this individual effectively expresses a unique combination of both parental traits. This contrasts with incomplete dominance, where the resulting phenotype is a blend, rather than a side-by-side exhibition of both alleles.

Multiple Alleles

Genetics often portrays two possibilities, like a coin with heads and tails. However, the situation is not always as binary; sometimes, there's a whole range of potential outcomes, much like a spinner with multiple options. This is explained by the concept of multiple alleles. In nature, many genes have more than just two alleles in the population, resulting in a wider variety of possible genetic combinations, and thus, phenotypes.

Probably the most relatable example of multiple alleles is the ABO blood group system of humans. Unlike traits controlled by two alleles, the ABO blood system is governed by three: A, B, and O. These alleles can combine in various ways to produce four different blood types: A, B, AB, and O. Each combination corresponds to a particular set of antigens on the red blood cells and the type of antibodies a person's plasma contains. The variety of combinations provided by multiple alleles contributes significantly to the genetic diversity seen among individuals within a population.