When any of the three or more allelic forms of a gene occupy the same locus in a given pair of homologous chromosomes, they are said to be called multiple alleles.

(a) Locus: A specific location of genes on a chromosome.
(b) Centimorgan: Unit of distance in a genetic map.

The diagrammatic representation of position of genes and related distances between the adjacent genes is called genetic mapping.

\(RF=\frac { Number \ of\ recombinants }{ Number\ of\ offsprings } \times 100\\ \)

After crossing over, chiasma starts to move towards the terminal end of chromatids. This is known as terminalization. As a result, complete separation of homologous chromosomes occurs.

Failure in the formation of synaptonemal complex leads to the. absence of crossing over to take place. It is noticed in certain male species of Drosophila.

Synaptonemal complex is a highly organised structure or filaments that facilitates the synapsis and chiasma formation during crossing over mechanism.

During zygotene stage of prophase I of meiosis I, homologous chromosomes are aligned side by side resulting in a pair of homologous chromosomes called bivalents.

Crossing over is a precise process that includes stages like synapsis, tetrad formation, cross over and terminalization.

No. Though crossing over is a common process in germinal cells rarely it also occurs in somatic cells during mitosis. Such crossing over is called mitotic crossing over or somatic crossing over.

The term 'crossing over' was coined by Morgan (1912). It takes place during pachytene stage of prophase I of meiosis.

Genes located close together on the same chromosome and inherited together are called linked genes.

The two genes that are sufficiently far apart on the same chromosome are called unlinked genes or syntenic genes. Such condition is known as synteny.

Tendency of genes to remain together during separation of chromosomes is called linkage. Linkage are of 2 types - complete linkage and incomplete linkage.

(a) Hugo de Vries proposed Mutation theory.
(b) Sutton and Boveri proposed chromosomal theory of inheritance.