Question

Karl Landsteiner and Philip Levine discovered a glycoprotein expressed on the surface of red blood cells, which exists in two forms, \(M\) and \(N .\) An individual may produce either one or both of them. The alleles \(L^{M}\) and \(L^{N}\) control the expression of the glycoprotein. What type of inheritance does the MN blood group exhibit, and what are the genotypes of the phenotypes observed in the human population?

Short answer

Answer: The MN blood group exhibits co-dominant inheritance. The possible genotypes are \(L^{M}L^{M}\) (expression of M glycoprotein only), \(L^{N}L^{N}\) (expression of N glycoprotein only), and \(L^{M}L^{N}\) (expression of both M and N glycoproteins).

Step-by-step solution

Identify the type of inheritance

From the information given, we know that individuals can produce one or both glycoproteins on the surface of their red blood cells, indicating that the glycoprotein is inherited via a co-dominant trait. This means that both alleles \(L^{M}\) and \(L^{N}\) are expressed when they are present together, resulting in individuals displaying the M, N, or both phenotypes.

Determine the possible genotypes

Now that we know the MN blood group exhibits co-dominant inheritance, we need to list the possible genotypes that result from the combinations of the alleles \(L^{M}\) and \(L^{N}\). Using the 2 alleles, we can create the following genotypes: 1. Homozygous dominant for M: \(L^{M}L^{M}\) 2. Homozygous dominant for N: \(L^{N}L^{N}\) 3. Heterozygous for both M and N: \(L^{M}L^{N}\)

Determine the phenotypes corresponding to the genotypes

Each genotype results in a specific phenotype. In this case, we have: 1. Homozygous dominant for M (\(L^{M}L^{M}\)): Expression of M glycoprotein only 2. Homozygous dominant for N (\(L^{N}L^{N}\)): Expression of N glycoprotein only 3. Heterozygous for both M and N (\(L^{M}L^{N}\)): Expression of both M and N glycoproteins (due to co-dominance) In summary, the MN blood group exhibits co-dominant inheritance with the possible genotypes being \(L^{M}L^{M}\), \(L^{N}L^{N}\), and \(L^{M}L^{N}\). These genotypes result in the following phenotypes: expression of M glycoprotein only, expression of N glycoprotein only, and expression of both M and N glycoproteins.

Key concepts

Co-dominant inheritance

Co-dominant inheritance is a fascinating concept in genetics where both alleles in a gene pair contribute equally to the phenotype of an organism. This means that neither allele is dominant or recessive, but instead, both are expressed simultaneously. A classic example of co-dominant inheritance is the MN blood group system, where individuals can express both the M and N glycoproteins on their red blood cells. In such cases, if an individual inherits the alleles for both M and N, both alleles are actively expressed, giving rise to a distinct phenotype.

In co-dominance, each of the alleles maintains its own identity and can be observed in the phenotype. When looking at the inheritance pattern of the MN blood group, a person with the genotype \( L^{M}L^{N} \) would express both the M and N glycoproteins, illustrating the hallmark of co-dominant traits. Understanding co-dominant inheritance helps us recognize that genetic diversity is not just a matter of dominant and recessive traits. Instead, it emphasizes the complexity and richness of genetic expression in living organisms.

MN blood group

The MN blood group is a particular system within human blood grouping that revolves around the presence of glycoproteins M and N on the surface of red blood cells. Discovered by Karl Landsteiner and Philip Levine, this blood group is determined by the interaction of alleles at the glycoprotein locus.

Humans can have three possible genotypes in terms of the MN blood group: homozygous M (\( L^{M}L^{M} \)), homozygous N (\( L^{N}L^{N} \)), and heterozygous (\( L^{M}L^{N} \)). Here's what they mean:

• People with two M alleles (\( L^{M}L^{M} \)) have only M glycoprotein on their red blood cells.
• Individuals with two N alleles (\( L^{N}L^{N} \)) have only N glycoprotein expressed.
• Those with one M and one N allele (\( L^{M}L^{N} \)) showcase the co-dominant inheritance by displaying both M and N glycoproteins.

This MN system emphasizes genetic diversity through its co-dominant inheritance pattern, providing a clear, straightforward example of how differing alleles at a genetic locus can influence observable characteristics.

Alleles

In genetics, alleles are alternative forms of a gene that reside at a specific locus on a chromosome. Alleles determine distinct traits that can be passed from parents to offspring. Each individual inherits two alleles for each gene, one from each parent.

The concept of alleles becomes particularly engaging when we explore blood group systems like the MN group. Here, the alleles \( L^{M} \) and \( L^{N} \) are responsible for the presence of M and N glycoproteins on red blood cells. This is a clear illustration of how different alleles can affect the phenotypic expression of a trait in a co-dominant manner.

It's important to understand:

• Alleles can bring about variation in traits observed between individuals.
• Despite being different, alleles \( L^{M} \) and \( L^{N} \) in the MN blood group both get expressed when present together, showcasing co-dominance.
• Alleles are key to understanding genetic inheritance patterns and how traits are transmitted through generations.

The study of alleles not only aids in comprehending simple traits but also leads to insights into complex inheritance patterns, crucial for fields such as genetics and evolutionary biology.