ABO blood group alleles can be dominant, recessive, or co-dominant:
The red blood cells of plasma membrane contain sugars that are interconnected on the surface of antigens. An antigen acts as molecular structures that are recognized by the antibodies of immune system. The two type of antigens present are A and B. The surface antigen synthesis is regulated by the alleles of I A and I B. However, i allele is recessive to both I A and I B. In humans, ABO blood group type antigens are an example of multiple alleles, which determines blood type in humans. Moreover, it illustrates the allelic relationship of co-dominancE.The following diagram depicts the alleles of ABO blood groups:
When serum from individual 1 agglutinates red blood cells from individual 2, the possible genotypes could be:
• If individual 1 is ii , individual 2 could be I A i, I A I A ,I B i, I B I B , or I A I B.
• If individual 1 is I A i or I A I A , individual 2could be I B i, I B I B ,I B i or I A I B.
• If individual 1 is I B i or I B I B , individual 2could be I A i, I A I A or I A I B.
For instance, on assuming individual 1 is the parent of individual 2.
• If individual 1 is ii , individual 2 could be I A i or I B i.
• If individual 1 is I A i , individual 2could be I B i or I A I B.
• If individual 1 is I A I A , individual 2could be I A I B.
• If individual 1 is I B i, individual 2could be I A i, or I A I B.
• If individual 1 is I B I B , individual 2could be I A I B.
Typically Mexican hairless dogs that have little hair and few teeth are heterozygous for a dominant allele. These genes are lethal when occur in homozygous condition. When two Mexican hairless dogs were mated to each other, we can expect 50% of the total offsprings to be hairless, 25% offsprings to be normal, whereas 25% offsprings diE.
The 12:3:1 ratio suggests that this is dominant epistasis cross. Begin by assuming that black is dominant over some unknown color, and black must be expressed before an allele in Gene 2.
Step 1: Designate the alleles:
Black chaff: B
Unknown color chaff: b
Gray chaff: G
White chaff: w
Step 2: Construct a Punnett square.
Add the phenotypes to each combination to see if the inheritance pattern gives 12:3:1 ratio specified in the problem.
Step 3: Analyze this type of inheritance pattern.
From the Punnett square, we see that the data fit our original assumption and reveal the genotype that produced the gray phenotype.
Step 4: Analyze this type of inheritance pattern at the level of protein function.
Dominant epistasis involves the interaction of genes. The proteins produced by these genes can interact with one another. For example, the protein encoded by one gene can modify the protein encoded by another gene.
Another possibility is that two different proteins may act in unison to get a certain reaction. If only one protein is present, a certain biochemical reaction occurs, but if two link up, the resulting reaction might occur differently or not at all. In any case, such interactions can do change the patterns of inheritancE.