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How are genes transmitted between relatives instead of blood itself?

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consanguinity (Left) Absence of inbreeding: horizontal lines connect mates, vertical lines connect parents with their child; (right) an inbreeding loop: horizontal bar at top of loop connects brother and sister, all other lines and bars as above

The term "consanguinity" is derived from the Latin for "of common blood," but this is biologically inaccurate. In reality, relatives do not transmit blood to one another; rather, they share genetic material inherited from common ancestors.1

Genes are transmitted through chromosomes located within the cell nuclei. These chromosomes are composed of proteins and DNA, which carries the coded instructions for biological traits. During meiosis—the specialized cell division that produces sperm and egg cells—chromosomes are shuffled and exchanged through a process called crossing over. This ensures that offspring receive a unique combination of genetic information from each parent.123

Because relatives share common ancestors, they possess a higher probability of sharing specific genotypes or genetic characteristics. The degree of this relatedness depends on how many ancestors are shared and the chance elements involved in the transmission of chromosomes during meiosis.12