Blood Bank Genetics: Immunohematology Practice

Comprehensive vocabulary flashcards covering basic genetic terms, Mendelian laws, population genetics, and inheritance patterns specifically applied to immunohematology.

Allele

A variant form of a specific gene representing different DNA sequences at a given genomic location; for example, A, B, and O are allelic.

Phenotype

The observed physical traits or expression, such as specific red blood cell (RBC) antigens (ABO, Rh, Kell) detected on the surface of a person's cells, often seen as agglutination in blood banking.

Genotype

The specific genetic makeup or set of alleles (e.g., BB, Bb, bb) an organism inherits, identified through molecular DNA techniques like PCR or bead chip arrays.

Homozygous

A genetic state where both inherited alleles are identical (e.g., KK, kk), which can produce a stronger expression of the gene (dosage).

Hemizygous

A genetic state where an individual’s chromosome has only one copy of a specific gene instead of two because the other chromosome's allele is deleted or absent; males are hemizygous for X-linked diseases.

Heterozygous

Inheriting two different alleles for a specific blood group antigen (e.g., Jka and Jkb), which results in a single dose of each antigen and can make them weaker or harder to detect in the laboratory.

Dominant allele

An allele that expresses its phenotype even if an individual only inherits one copy (homozygous or heterozygous states), masking the presence of a recessive allele.

Recessive allele

An allele that is only expressed when an organism inherits two identical copies (homozygous state).

Co-dominance

A genetic inheritance pattern where two different alleles are simultaneously and fully expressed rather than one masking the other, such as in the ABO or MNSs blood group systems.

Amorphic mutation (Amorph)

Also known as a "null allele" or "silent gene," this is a loss-of-function mutation where the altered gene completely loses its ability to produce a functional protein or antigen.

Mendel's First Law (Law of Segregation)

States that during gamete formation, the two alleles for an inheritable character separate so that each gamete receives only one allele.

Mendel's Second Law (Law of Independent Assortment)

States that allele pairs separate independently during gamete formation, meaning the inheritance of one trait does not affect another provided the genes are on different chromosomes.

Linkage

Occurs when two genes sit very close together on the same chromosome and tend to travel together during meiosis as a unit rather than separating independently.

Haplotype

A "package deal" of genes inherited together as a unit due to linkage, such as the Rh system genes for D, C/c, and E/e on chromosome 1.

Phenotypic frequency

The percentage or frequency of a specific antigen detected within a tested population, used to estimate donor availability and compatibility.

Hardy-Weinberg Equilibrium

A principle stating that gene frequencies stay stable over time in a population that is large, randomly mating, and free of genetic pressures like mutation, migration, or selection.

Hardy-Weinberg Formula

$p + q = 1$ and $p^2 + 2pq + q^2 = 1$, where $p$ is the frequency of the dominant allele and $q$ is the frequency of the recessive allele.

Autosomal Recessive

An inheritance pattern where the phenotype is expressed only when the recessive gene is inherited from both parents, such as the Bombay blood group (Oh) or Rh-negative (dd) status.

Autosomal Dominant

An inheritance pattern where a single copy of a gene on a non-sex chromosome causes the trait to be expressed; examples include the suppressor gene In(Lu).

X-linked Recessive

A genetic mechanism involving a mutation on the X chromosome; males who inherit the X will express the trait, while females can be carriers without expression.

X-linked Dominant

A mode of inheritance where a mutation in a single gene on the X chromosome causes the trait in both males and females; and affected fathers pass it to all of their daughters, such as the Xga blood group.

Autosomes

The 22 pairs of non-sex chromosomes found in humans.

Sex Chromosomes

The single pair of chromosomes (XX or XY) that determine the sex of an individual and differ in size and genetic composition.

Dosage effect

Phenonmenon where homozygous cells produce a stronger expression of an antigen than heterozygous cells, often making homozygous cells preferred for antibody rule-outs (e.g., Kidd, Duffy, Rh, MNS).