Consanguinity

Mutations that cause recessive diseases arise and are maintained in populations in two ways:

1. consanguinity

2. balanced polymorphism

In consanguinity, the mutations that cause recessive diseases are maintained because the individuals inbreed in consanguinity; the genes are never lost in the family they are passed on to their offspring, to generations and they are always kept in the family.

Mating between relatives. First cousin marriages for example. The offspring produced in this type of mating are called inbreed. Their offspring have a high chance of becoming affected by autosomal recessive disorders in consanguinity. Consanguinity does not play a role in autosomal dominant diseases.

Two doses of a bad autosomal dominant gene has the ability to produce more severe phenotype of the single-dose syndrome (meaning, of the syndrome that develops with only one single dosage of a bad autosomal dominant gene) or even worse, cause death before birth.

References:

1) Biology. Seventh Edition, Neil A. Campbell and Jane B. Reece. Pearson Eduction Inc., publishing as Benjamin Cummings, 1301 Sansome St., San Franscisco, CA

2) Biology. Peter H. Raven, George B. Johnson, Susan Singer, Jonathan Losos. McGraw-Hill Science/Engineering/Math; 7 edition (January 8, 2004)

3) DNA Science: A First Course, Second Edition. David A. Micklos. Cold Springs Harbor Laboratory Press; 2 edition (January 8, 2003)