Question

Write all theoretically possible genotypes of children (and their chance) if the persons with the following two blood phenotypes marry: A Rh+, AB Rh-.

Answer 1

Answer: If the blood group of person is A that means, the person has IA allele on one chromosome and and IA or i allele on another chromosome. Hence the possible genotypes will include IAIA, IAi and since the D antigens will also be there as the person is Rh positive, D antigen is a dominant allele, it will be expressed in homozygous DD as well as heterozygous condition Dd.

Hence there are following different possibilities of the genotypes;

The genotype of the person with A Rh +ve can be IAi DD or IAi Dd or IAIADD or IAIADd

The person with AB genotype will have A allele on one chromosome and B allele on another chromosome hence the person will have one possible combination of alleles i.e. IAIB and since the person is Rh –ve , the genotype will for D antigen will be dd as with d antigen in homozygous condition will be Rh -ve

Hence the genotype of the person with AB Rh-ve can be IAIBdd

We will have to consider different crosses since, the person with A Rh +ve can show different genotypes, while person with AB Rh –ve has only one possibility.

Case I ) If the A Rh +ve has genotype= IAi DD,

The gamates produced will be IA D and iD

genotype of the person with AB Rh-ve is IAIBdd

the gamates produced will be IAd and IBd

hence the cross would be

gamates	IA D	iD
IAd	IA IA Dd A Rh +ve	IAi Dd A Rh +ve
IBd	IAIB Dd AB Rh +ve	IBiDd B Rh +ve

In this case 50% offspring will have A Rh+ve phenotype; 25% will have B Rh +ve and 25% will have AB Rh +ve

Case II ) If the A Rh +ve has genotype= IAi Dd,

The gamates produced will be IA D , IA d, iD and id

genotype of the person with AB Rh-ve is IAIBdd

the gamates produced will be IAd and IBd

hence the cross would be

gamates	IA D	IA d	iD	id
IAd	IA IA D d A Rh +ve	IA IAdd A Rh -ve	IAiD d A Rh +ve	IAid d A Rh -ve
IBd	IAIB D d AB Rh +ve	IAIB d d AB Rh -ve	IBiD d B Rh +ve	IBid d B Rh -ve

In this case 25% will be A Rh +ve; 25% will be A Rh –ve; 12.5% will be AB Rh +ve and 12.5% will be AB Rh –ve; 12.5% will be B Rh +ve and 12.5% will be B Rh -ve

Case III ) If the A Rh +ve has genotype= IAIADD

The gamates produced will be IA D

genotype of the person with AB Rh-ve is IAIBdd

the gamates produced will be IAd and IBd

hence the cross would be

gamates	IA D
IAd	IA IAD d A Rh +ve
IBd	IA IBD d AB Rh +ve

50% will be A Rh +ve and 50% will be AB Rh+ve

Case IV ) If the A Rh +ve has genotype= IAIADd

The gamates produced will be IA D and IAd

genotype of the person with AB Rh-ve is IAIBdd

the gamates produced will be IAd and IBd

hence the cross would be

gamates	IA D	IAd
IAd	IA IA Dd A Rh +ve	IAIAdd A Rh -ve
IBd	IA IB Dd AB Rh +ve	IAIBdd AB Rh-ve

In this case 25% A Rh +ve25% A Rh –ve; 25%AB Rh +ve and 25%AB Rh +ve

Note:please ask if you have any doubts in the comments section.