Genetic Principles in Blood Banking

Vocabulary and key concepts covering genetic inheritance patterns, blood group systems, and population genetics calculations as applied in blood banking.

Blood group systems

Groups of antigens on the RBC membrane that share related serologic properties and genetic patterns of inheritance.

Phenotype

The physical expression of traits.

Genotype

The actual genetic makeup of an individual.

Punnett Square

A tool used to predict the probability of an offspring’s genotype by summarizing every possible combination of maternal and paternal alleles of a particular gene.

Gene

The basic unit of inheritance found on a chromosome.

Locus

The specific site at which a gene is located on a chromosome.

Alleles

Alternative forms of a gene found at each locus.

Antithetical

Antigens produced by opposite alleles, such as Kpa and Kpb antigens.

Polymorphic

A term describing a single locus that has multiple alleles.

Recessive

An inheritance pattern where a gene is expressed only when inherited from both parents.

Codominant

An inheritance pattern characterized by the equal expression of two different alleles.

Dominant

An inheritance pattern where one gene is expressed over another gene.

Independent segregation

Occurs when one gene from each parent is passed to the offspring.

Independent assortment

Demonstrated when blood group antigens from different chromosomes are expressed separately, resulting in a mixture of genetic material.

Crossing over

Occurs when 2 genes on the same chromosome combine and produce 2 new chromosomes.

Linkage

Occurs when 2 genes that are close to each other are inherited together.

Haplotype

Each set of linked genes inherited together.

Linkage disequilibrium

A phenomenon where haplotypes occur at a higher frequency than would be expected for unlinked genes.

Xg system inheritance

Located on the X chromosome; if the father carries the allele, he passes it to all daughters but no sons. If the mother carries it (and not the father), all children will express it.

Homozygous

An individual who inherits identical alleles, such as $\text{AA}$, $\text{BB}$, or $\text{MM}$ ($\text{M+ N–}$).

Heterozygous

An individual who inherits different alleles, such as $\text{AO}$, $\text{AB}$, or $\text{MN}$ ($\text{M+ N+}$).

Dosage

A variation in antigen expression due to the number of alleles present, often resulting in stronger agglutination in homozygous ($\text{double dose}$) expressions.

Hardy-Weinberg Basic Formula

Used to represent gene frequency where $p + q = 1$ ($p$ is allele #1, $q$ is allele #2).

Hardy-Weinberg Genotype Proportions

The formula used to calculate genotype proportions: $p^2 + 2pq + q^2 = 1.0$.

Phenotype Calculation

A calculation used to find a unit of RBCs with specific characteristics by converting the known percentage of antigen-negative individuals to decimals and multiplying them (e.g., $0.30 \times 0.70 \times 0.45 = 0.0945$).