Question

What is my blood type if both the parents are O positive?

Answer 1

Whether a person has type A, type B, type AB or type O blood depends on the presence or absence of specific substances on the red blood cells. There are two of these substances- antigen A and B. Thus a person with antigen A is considered to be with blood group A, a person who is with blood group O has neither of the antigens and a person with antigen B, blood type is named B. If both the antigens A and B are present the blood group is called AB.

Complete answer:
The blood type character is controlled by a group of three alleles. The gene which produces antigen A is denoted by $I^A$, the gene for antigen B by $I^B$, and the gene for absence for both the antigens by I.
The genes $I^A$ and $I^B$ are both dominant over gene $I^O$ or I, but not over each other. Any person carries two of those alleles, one from each parent.

$I^A$ determines the formation of glycoprotein A and $I^B$ determines the formation of glycoprotein B. The dominant relationship of three alleles is interesting. Both $I^A$ and $I^B$ are fully expressed within the presence of the opposite. Both $I^A$ and $I^B$ are dominant to I and it is only when both $I^A$ and $I^B$ are absent (i.e. with genotype ii) a person is with blood group O. Since a person with genotype $I^AI^B$ produces both the glycoproteins, alleles $I^A$ or $I^B$ are said to be co dominant.

By knowing the blood group of a couple, blood groups of their children can be predicted.

If mother and father both have ii and ii genotype then after crossing over the child will have ii genotype only. So If mother and father both are O positive then their child will also be O positive.

Genotypes- mother (ii) × father (ii)
Child Genotype- ii

Note:
It has been noticed that for many characters a gene for a character may exist in many alternative alleles. These sorts of genes are thanks to mutation of one wild type. When more than two allelic forms of wild type are located on the same locus in a given pair of chromosomes, they are known to compose the series of multiple alleles.