Why Are The Fingerprints Of Identical Twins Not Identical?

Identical twins are formed when a single egg that is fertilized divides into two or more after conception and since they are formed from a single zygote (egg) they have the same genetic characteristics. But fingerprints are not characterized by genetics. It is actually determined by the interaction of the genes of the individual and the environment in the uterus and since identical twins develop in different environments their fingerprints are different. 
The final pattern of fingerprints are thought to be influenced by environmental factors such as nutrition, blood pressure, position in the womb and the rate of growth of the fingers. You may find similar patterns of ridges and whorls but there will be differences.

Why Is There No Incidence Of Heart Cancer?

Cancer is a tumor and tumors can be either benign (non-cancerous) or malignant (cancerous). Malignant tumors are further classified as primary or secondary, that is, whether it arises in the organ itself or spread from other organs. There are incidences of cancer of the heart and if it does occur it is usually benign such myxomas (the most common), fibromas, rhabdomyomas, and hamartomas. Malignant tumors of the heart such as angiosarcoma or cardiac sarcoma are know occur but are extremely rare. In fact any tumor of the heart is extremely rare. In a study of 12,487 cases where autopsies were performed only 7 tumors were found. Benign tumors of the heart can be surgically removed and the success rate is almost 100%. The success rate of the treatment of a malignant tumor of the heart depends on the further spread of the cancer to other vital organs.

How Is Blood Grouping Done?

The broad classification of the groups or types is based on the presence or absence of particular antigens that are carried on the surface of red blood cells. Corresponding antibodies are carried in the blood plasma. Broadly the types are A, B, AB and O but the International Society of Blood Transfusion recognizes some thirty types fro the purposes of blood transfusion - the process of transferring blood taken from one person to another person.

A person with a particular antigen in his blood cannot have the same antibody. Thus a person with  blood containing the antigen A cannot have the antibody A in his blood.

A person of the blood group A has the antigen A and the antibody B. Similarly a person belonging to the blood group B will have the antigen B and the antibody A. The person belonging to the blood group AB will have only the antigens A and B and  no antibodies. The person of the blood type O has only the antibodies A and B and no antigens.

Another type of blood group is the Rh blood group. This name is derived from the group first discovered in the Rhesus monkey. In this group there is the Rh Positive and the Rh Negative blood groups.

The other blood groups include the A1 Positive (A1 +ve), A1 Negative (A1 -ve), A2 Positive, A2 Negative, B Positive, B Negative, O Positive and O Negative to name a few.

How Long Can Humans Survive Without Oxygen?

On the whole, oxygen is absolutely required for survival. Loss of oxygen to any part of the body is known as hypoxia. Total loss of oxygen results in anoxia.

Due to the susceptibility of the human brain to oxygen, humans can survive for only a short period of time without a supply of oxygen to the brain. In spite of the fact that the brain weighs only 5% of the body's weight, it consumes some 20% of all the oxygen intake. Oxygen is supplied to the brain by blood. It takes only about 8 to 10 seconds of loss of oxygen to the brain to make us lose consciousness. Loss of oxygen to the brain for a period of 4 to 6 minutes results in destruction of the brain cells. Extended periods of time results in brain damage and ultimately death.

The brain can survive for longer periods of time at lower temperatures. That is due to the fact that at lower temperatures the brain requires less oxygen for its survival. This fact is made of use in major surgeries and is known as induced hypothermia.

The other tissues of the body can survive for longer periods of time without oxygen, which make organ transplantation possible.