Disorders in chromosome number, or aneuploidies, are typically lethal to the embryo, although a few trisomic genotypes are viable. The Chromosomal Theory of inheritance, proposed by Sutton and Boveri, states that chromosomes are the vehicles of genetic heredity.

Sturtevant devised a method to assess recombination frequency and infer the relative positions and distances of linked genes on a chromosome on the basis of the average number of crossovers in the intervening region… Whereas linkage causes alleles on the same chromosome to be inherited together, homologous recombination biases alleles toward an inheritance pattern of independent assortment

Chromosomal Theory of Inheritance — theory proposing that chromosomes are the vehicles of genes and that their behavior during meiosis is the physical basis of the inheritance patterns that Mendel observed. homologous recombination — process by which homologous chromosomes undergo reciprocal physical exchanges at their arms, also known as crossing over. recombination frequency — average number of crossovers between two alleles; observed as the number of nonparental types in a population of progeny. X inactivation — condensation of X chromosomes into Barr bodies during embryonic development in females to compensate for the double genetic dose.