allele:

One version of a gene at a given location (locus) along a chromosome.

allele frequency:

(synonym: gene frequency) The proportion of individuals in a population who have inherited a specific gene mutation or variant.

allelic heterogeneity:

(synonym: molecular heterogeneity) Different mutations in the same gene at the same chromosomal locus that cause a single phenotype.

alpha thalassemia:

The majority of adult hemoglobin contains two types of protein subunits, alpha globin and beta globin. Defects in the alpha-globin chain lead to alpha thalassemia, with the general complications of thalassemia and alpha-thalassemia specific features. Alpha globin is encoded by two virtually identical genes (HBA1 and HBA2), which with two sets of equivalent chromosomes results in four functional copies of the alpha-globin gene in humans. Defects in one or up to all four copies of the alpha-globin gene lead to alpha thalassemia with increasing degrees of severity. A defect in one copy results in alpha minor (also called alpha+ thalassemia trait or alpha-thalassemia trait type 2) and symptomless carrier status, defects in two copies result in mild anemia (alpha-thalassemia trait type 1), defects in three copies give Hemoglobin H disease with anemia and enlarged spleen, and defects in all four copies result in prenatal or neonatal death. See also thalassemia, heterozygous, and homozygous. For further details, please see the Thalassemia Primer featured on this portal.

anisocytosis:

Variation in the size of RBCs, measured by an increased RBC distribution width (RDW).

autosomal:

Refers to any of the chromosomes other than the sex-determining chromosomes (i.e., X and Y) or the genes on these chromosomes.

autosomal dominant:

Describes a trait or disorder in which the phenotype is expressed in those who have inherited only one copy of a particular gene mutation (heterozygotes); specifically refers to a gene on one of the 22 pairs of autosomes (non-sex chromosomes).