Genetics, blood type gene has two alleles, each allele has genotype A, B or O. The A and B are dominant, and O is recessive. So allele A combined with allele O is type A. Similarly, BO is type B, AA is type A, BB is type B, OO is type O, and AB is typeAB.
If both parents have type A blood, then the alleles could be AA or AO, thus the allele A frequency is 75%, allele O frequency is 25% for both parents. So the chance of alleles OO is 25% × 25% = 6.25%, alleles AA is 75% × 75% = 56.25%, alleles AO is 75% × 25% = 18.75%, alleles OA is 25% × 75% = 18.75%. Since AA, AO and OA are blood type A, and OO is blood type O, thus their child has 6.25% chance to be blood type O and 93.75% chance to be blood type A.
The +/- is called the rhesus factor, with + being dominant, and - being recessive. So if both parents are -, the kids are always -, otherwise the kids might be + or -.
Child Blood Type Estimate Table: Father's Blood TypeABABOMother's Blood TypeAA/OA/B/AB/OA/B/ABA/OBA/B/AB/OB/OA/B/ABB/OABA/B/ABA/B/ABA/B/
The left side of the heart receives oxygenated blood from the pulmonary vein and pumps it into the aorta, while the right side of the heart receives deoxygenated blood from the vena cava and pumps it into the pulmonary vein. The pulmonary vein and aorta also have valves connecting them to their respective ventricle.
