4. The ABO blood type is controlled by a single locus, called I, and the human p

Question

4. The ABO blood type is controlled by a single locus, called I, and the human population harbors three alleles: 1', I, and I'. Each individual, of course, only carries two alleles at the locus. These alleles give rise to the blood type phenotypes, A, B, AB, and O. The relationship between genotype and phenotype is complicated. I is dominant to I°, I is also dominant to r, and 14 and 18 are coloni inant, which means that the effect of both can be seen in the heterozygote a. Suppose that parents know their phenotypes: the father is type O and the mother is type B. What are the possible genobypes of these parents? b. What are the possible blood type phenobypes among their children? c. Suppose instead that the father is type B and the mother is type A, and again we don't have any data about their genotypes. What are the possible blood types among their children?

Explanation / Answer

a) We know that there are four blood type: A, B, O, AB. Human blood type is determined by co-dominant alleles. At a specific location on a specific chromosome of DNA, several different types of genetic information are called by an Allele. Each of us has two ABO blood type alleles because we each inherit one blood type allele from our biological mother and one from our biological father. A description of the pair of alleles in our DNA is called the genotype. There are a total of six different genotypes at the human ABO genetic locus. The different possible genotypes are AA, AO, BB, BO, AB, and OO. A blood test is used to determine whether the A and/or B characteristics are present in a blood sample. It is not possible to determine the exact genotype from a blood test result of either type A or type B. If someone has blood type A, they must have at least one copy of the A allele, but they could have two copies. Their genotype is either AA or AO. Similarly, someone who is blood type B could have, a genotype of either BB or BO.

if mother's blood type B then the possible genotype of mother BB, BO and if father's blood type O then the possible genotype is OO.

b) An allele is a form of a gene which codes for one possible outcome of a phenotype. Here the recessive is O. so the blood type phenotypes among their children are either B for genotypes of BB and BO or O for genotypes OO.

c) If the Mother's blood type is B, and the father's blood type is O, then their child must be either B or O. For instance, if both mother and alleged father have type A blood, then the child can only have A or O blood. On the other hand, if the mother's blood type is A, and the father is B, the child could be any of the four blood types A, B, AB or O so, in this case, the ability to predict paternity is reduced. When both father and mother contribute an A gene, their child has to Type A blood. then the child becomes "pure-bred" for the A gene and for this reason he or she can only pass on an A gene to his or her offspring. If one parent contributes and A gene and the other contributes an O gene, the child will have A blood type, but, like his parents, he'll also have both A and O genes that he may pass along to his children. However, in 1 out of 4 instances, both parents will contribute their recessive O gene to their child. When that happens, instead of the child expressing the A blood type, he will instead express the O blood type. Scientists use the term genotype to refer to the combination of mother and father genes in the person's make up. AA, AO and OO are the 3 genotypes that may result from the mating of the parents in the example above. Scientists use the term phenotype to refer to what gene is actually expressed. In the example above, there are 2 phenotypes of Type A blood and Type O blood. The type O blood phenotype can only result from one genotype of OO. But Type A blood can result from two different genotypes of AA and AO.

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