ALELISMO MÚLTIPLE: GRUPOS SANGUÍNEOS AB0

Understanding Multiple Allelism through Blood Groups

Introduction to Multiple Allelism

• The video introduces the concept of multiple allelism, using the ABO blood group system as a primary example.

• It highlights that traditionally, it was believed there were only two hereditary factors for each trait, but this has evolved with genetic understanding.

• The question posed is how multiple alleles can exist in diploid organisms.

ABO Blood Group System

• In diploid organisms, while only two alleles are present per gene, populations can exhibit more than two alleles; exemplified by the ABO blood group which has three alleles: A, B, and O.

• The gene for blood type is denoted by an uppercase "I," with superscripts A, B, and 0 representing the respective alleles.

Relationships Between Alleles

• The relationship between A and B alleles is one of codominance; both can be expressed simultaneously in individuals with AB blood type.

• Conversely, allele O is recessive to both A and B; thus it does not manifest unless homozygous.

Phenotypes and Genotypes

• There are four possible phenotypes based on combinations of genotypes: A (homozygous or heterozygous with O), B (homozygous or heterozygous with O), AB (heterozygous), and O (homozygous).

• Antigens produced on red blood cells correspond to these genotypes: Type A produces antigen A, Type B produces antigen B, Type AB produces both antigens, while Type O produces none.

Genetic Problem Solving Example

• The video transitions into solving a genetics problem from a biology exam regarding inheritance patterns related to blood types.

• Key data points include identifying genes involved (blood group), their corresponding alleles (A, B, 0), relationships among them (codominance vs. dominance), and recognizing the type of inheritance as multiple allelism.

Analyzing Family Blood Types

• The scenario involves a man questioning paternity based on his children's blood types; he recognizes children with groups 0 and AB but questions another child with group B.

• It explains that for a child to have phenotype 0 (recessive), both parents must carry allele 0. Additionally, one parent must carry allele A while the other carries allele B.

This structured approach provides clarity on complex genetic concepts surrounding multiple allelism using practical examples from human genetics.