Answer
Chromosomes come in pairs. This means that each of the 46 chromosomes in a human diploid cell is paired with a partner or sister chromosome of similar size and shape. Chromosomes of the same size and shape are called homologous chromosomes. These"sister" chromosomes not only have the same appearance, but they have been shown to code for genes for alternative traits of a kind, and are found at the same loci or position. Their centromeres are also located at corresponding points along the length of the sister chromosomes.
Work Step by Step
A pair of homologous chromosomes derive from different parents--one from the paternal parent and one from the maternal parent. Regarding loci, the genes that code for alternative forms of a particular kind of trait ( say hemoglobin) are situated at corresponding positions or loci on homologous chromosomes. For example, ear wax type and size of ear lobe of an individual is determined by the interaction of single genes at a specific locus (position) on homologous chromosomes. Not many human traits are inherited after a simple monogenic pattern. This means that most human traits such as height, body type, even eye color and hemoglobin type are influenced by several genes . Some diseases like adult polycystic kidneys, ear lobe size, consistency of ear wax (wet/ dry) , seem to be monogenic and to be controlled by two alleles say "E" for the dominant gene ( for dry ear wax) and "e" for the recessive allele coding for wet ear wax.. If his were the case then these genes would occupy corresponding positions on homologous chromosomes of say chromosome pair #16, position 11. At this specific locus a given individual could have the genotypes "EE", "Ee" or "ee"; if the "E" allele is dominant to the "e" allele, then all persons possessing genotypes with the "E" gene would have dry ear wax, and only people with the double recessive genotype, "e" would have wet ear wax.
