8. Glossary

Bivalent: A pair of homologous chromosomes before their duplication in meiosis. It is also called diad.

 

Cell division: The three types of cell division that occur in animal cells are amitosis (direct division), mitosis (indirect division) and meiosis (reduction division).

 

Centromere: A structure present in between the chromosomal arms of chromosomes to which the mitotic and meiotic spindle microtubules are attached. It is called kinetochore or primary constriction.

 

Chiasma: The point of contact and interchange between chromatids of two homologous chromosomes.

 

Chromatids: One of the two identical longitudinal halves of a chromosome share a common centromere with a sister chromatid.

 

Chromosome: They are elongated rod-like structures formed during nuclear division. They represent the physical sites of nuclear genes, which are arranged in linear order. Every species has a characteristic number of chromosome.

 

Crossing over: Process in which genes are exchanged between non-sister chromatids of homologous chromosomes.

 

Diploid: An individual or cell having twocomplete sets of chromosomes.

 

Haploid: An individual or cell having a single complete set of chromosome.

 

Homologous chromosome: Chromosomes are occurring in pairs, one derived from each of the two parents. Each member of such a pair is the homolog of the other.

 

Interphase: It is the longest resting phase of the cell between two cell divisions.

 

Synapsis: Pairing of homologous chromosomes occurring in prophase -I of meiosis.

 

Tetrad: Four haploid cells arising from meiosis formed from four associated chromatids during synapsis.