Final answer:
A patient with two bands for the D17S855 marker indicates that they have two different alleles at that genomic location, making them heterozygous.
Step-by-step explanation:
A patient with two bands for the D17S855 marker is heterozygous for that genetic locus.
In genetics, the term heterozygous refers to having two different alleles for a given gene on the homologous chromosomes. When a DNA test shows two bands for a specific genetic marker such as D17S855, this means that the individual has two different versions (alleles) of the genetic sequence at that locus – one from each parent. This is distinct from a homozygous condition, where there would be only one band displayed, indicating that both alleles are the same.
Heterozygous individuals can express varied traits, depending on whether the alleles are dominant, recessive, or codominant. In contrast, hemizygous refers to the presence of only one allele, typically in genes found on sex chromosomes in one of the sexes, such as males with the X-linked genes. Lastly, nullizygous is used to describe a situation where both copies of a gene are missing, which is extremely rare.