Males have an X and a Y, females have two X's. When two genes are located on the same chromosome, they are usually transmitted together, and are thus Linked . At the start of Meiosis, Synapsis occurs and homologous chromosomes form pairs with their long axes parallel and the chromosomes have duplicated to form two chromatids. Chromosome breakage or some other event allow the broken chromatids to rejoin in a mixed manner. There can be multiple crossovers along a single chromosome.
Interference can either increase or decrease the probability of correlated crossovers.
The closer two genes or markers are together, the less likely a crossover event will occur between them to Unlink them. These chromosome can be ordered along a chromosome to produce a genetic map. Nucleotides are linked to each other by phosphodiester linkages between one nucleotide's phosphate group to a hydroxyl group on the sugar of an adjacent nucleotide. A and G are Purines and have a double ring structure, while C, T, and U are Pyrimidines and have a single ring structure. DNA is wound in a dobule helix with C's bonding to G's and A's bonding to T's and U's.