The B is ABO type and + is an Rh type (Rh positive). While these are medically the most important blood type systems, similarly we all have many others that we could typed for as well.

This suggests that natural selection, migrations, genetic drift, the founder principle, and non-random mating were all potentially important factors in our evolutionary history.

Blood types are acquired only by inheritance from parents and they cannot be changed. However, natural selection can have an effect on whether an individual survives to reproduce and pass on the alleles for his or her blood type.

The distribution of human traits regularly varies through time. In the 19th and 20th centuries, the development of inexpensive intercontinental travel along with the creation of millions of refugees that has resulted in an acceleration of population mixing.

Apparently, East Asians and Native Americans are the only people in the world who have the Diego positive blood type. This supports the hypothesis of an East Asian origin for Native Americans.

The typological model is scientifically unsound. The populational model is theoretically sound but of little value since we do not have distinct breeding populations. Only the clinal model explains most of human variation as we know it to be.

Advocates of this model construct clinal maps to visualize the gradual changes. An example is the clinal distribution of the B blood type allele in Europe.

With 2-4 broad traits, there can be millions who fit a racial type. However as the number of traits increases to 10 or more, very few people in the world will still fit the type. The more precisely a race is defined the concept becomes less useful.

Unlike such traits as skin colour and hair texture, blood comes in specific, non-blending types. There are no shades of difference--you cannot be halfway between type O and A.

Natural and social selection are very strong forces that can operate at the same time. There also can be the introduction or removal of genes from a population due to migration. In addition, genetic drift and other processes may be determining factors.

The populational model assumes that the only biologically distinct groups of people are those that have long breeding isolation. When the isolation breaks down, the genetic distinctness of such groups also ceases.

We are mostly the product of the combination of genes that we inherited from our parents. However, environmental influences also have an effect. For example, severely undernourished children are not likely to reach their full potential stature.

Type O is most common among Native Americans. However, type B is extremely low in Americans.

There will be a 50% chance (2 out of 4) of having a carrier (Aa) child. Similarly, each time there will be a 25% chance of having an offspring who will inherit the disease (aa) and die.

There are no distinct biological races of humans today. However, we still often misuse the concept to label each other. Commonly defined races usually are groups of people who share ethnic identity and some broad physical similarities.

All of the children will be healthy since none of them can be homozygous recessive (xx). However, there will be a 50% chance at each birth that the children will be carriers (Xx). The remaining 50% will be homozygous dominant (XX).

There is a 50% chance that the children will be heterozygous (Aa) and a 25% chance that they will be homozygous dominant (AA). Children with either of these genotypes will have this trait expressed in their phenotypes.

Since both parents are homozygous recessive (aa), all of their children will also express the trait. As a result, none of them will be free of this recessive trait in their phenotypes.

Modifying gene alters the effect of companion genes in the phenotype of an individual. A real life example is a gene that modifies the effect of a dominant cataract allele.

When genes have different effects depending on the gender of the parent from whom they were inherited, it is referred to as genome imprinting. Diabetes, psoriasis, and Prader-Willi syndrome are other examples of this phenomenon.

The gradual, more or less continuous change in hair colour from one group of aborigines to another is not random or haphazard. There probably is a progressive gradation because there are different evolutionary pressures from one region to another.

This distribution pattern is most likely the result of migration of groups of red-haired people into areas where other hair colours pre-dominated. However, it could also result from discriminatory marriage partner selection.

Except for monozygotic (identical) twins, it is highly likely that every one of us is genetically different from every other human whoever lived.

The International Society of Blood Transfusion (ISBT) identifies about 30 major blood group systems, including the ABO and Rh systems.

A gene would be called sex controlled if it is inherited by both males and females, but expressed differently in the phenotype of a boy and a girl.