The human MN blood group is determined by alleles (M and N) for a single gene that code for two specific, codominant markers found on the surface of red blood cells. If two individuals with the MN blood type produce offspring, which phenotypic ratio of offspring would result?

Rationale

50% MN; 25% NN; 25% MM

When two individuals with MN blood type (genotypes MN) reproduce, the expected phenotypic ratio of their offspring follows from a simple Mendelian cross. The combination of their alleles leads to a ratio of 50% offspring with the MN phenotype, 25% with the MM phenotype, and 25% with the NN phenotype.

A (50% MM; 25% MN; 25% NN) YOUR ANSWER

This ratio incorrectly suggests that there is a higher proportion of MM individuals. In a cross between two MN parents, the offspring can only inherit M or N alleles, making MM less frequent than MN.

B (100% MN) YOUR ANSWER

This option implies that all offspring would inherit the MN phenotype, which is not possible since the parents can also pass on the N allele. Therefore, there must be a variety of phenotypes resulting from both alleles.

C (50% MN; 25% NN; 25% MM) CORRECT

This is the correct answer, as it accurately reflects the results of a Punnett square analysis for a cross between two MN individuals. The expected offspring are 1 MM, 2 MN, and 1 NN, leading to the stated phenotypic ratio.

D (50% MM; 50% NN) YOUR ANSWER

This choice suggests that all offspring would be either MM or NN, neglecting the possibility of the MN phenotype. Given that both parents carry the MN alleles, this outcome is biologically implausible.

Conclusion

The inheritance of the MN blood group in offspring from two MN parents follows a classic Mendelian ratio of 1:2:1 when considering the codominance of the alleles. The correct outcome of 50% MN, 25% MM, and 25% NN highlights the diversity of phenotypes possible in the offspring, showcasing the principles of genetic inheritance and allele expression.

The human MN blood group is determined by alleles (M and N) for a single gene that code for two specific, codominant markers found on the surface of red blood cells. If two individuals with the MN blood type produce offspring, which phenotypic ratio of offspring would result?

50% MN; 25% NN; 25% MM

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