Genetic test
Cancer usually arises in a single cell. The cell's progress from normal to malignant to
metastatic appears to follow a series of distinct steps, each controlled by a different gene
or set of genes. Persons with hereditary cancer already have the first mutation. (external
link)
Scientists looking for a disease gene often begin by studying DNA samples from members of
'disease families' that have numerous relatives, over several generations, who have developed
an illness. (external link)
When a gene contains a mutation, the protein encoded by that gene will be abnormal. Some
protein changes are insignificant, others are disabling. (external link)
For a cell to make protein, the information from a gene is copied, base by base, from DNA
into new strands of messenger RNA (mRNA). Then mRNA travels out of the nucleus into the
cytoplasm, to cell organelles called ribosomes. There, mRNA directs the assembly of amino
acids that fold into completed protein molecule. (external link)
Each human cell contains 23 pairs of chromosomes, which can be distinguished by size and
by unique banding patterns. This set is from a male, since it contains a Y chromosome.
Females have two X chromosomes. (external link)
Different genes are activated in different cells, creating the specific proteins that give a
particular cell type its character. (external link)
Hereditary mutations are carried in the DNA of the reproductive cells. When reproductive
cells containing mutations combine to produce offspring, the mutation will be present in all
of the offspring's body cells. (external link)
Acquired mutations develop in DNA during a person's lifetime. If the mutation arises in a
body cell, copies of the mutation will exist only in descendants of that particular cell.
(external link)
In dominant genetic disorders, if one affected parent has a disease-causing allele that
dominates its normal counterpart, each child in the family has a 50-percent chance of
inheriting the disease allele and the disorder. (external link)
Genetic counseling:
bridging mutation and
social filter, by Lolita
Nikolova (.pdf)