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version of a gene


condition in which the organism has an abnormal number of copies of a chromosome

asexual reproduction

form of reproduction that does not involve fusion of gametes, producing offspring genetically identical to the parent


structure consisting of two sets of sister chromatids (from replicated homologous chromosomes) connected by the synaptonemal, ladderlike complex prior to the first meiotic division

chiasma (plural, chiasmata)

location on homologous chromosomes in a bivalent where crossing-over occurs


exchange of DNA between homologous chromosomes during meiosis


having a double set of chromosomes in homologous pairs. The diploid condition is designated by 2n.


union of sperm and egg


sex cell of a sexually reproducing organism, with a haploid set of chromosomes


production of gametes through the process of meiosis

germ-line cell

gamete or any of the precursor cells that divide to produce gametes


having a single set of chromosomes, which is half the total of the parent. The haploid condition is designated by 1n or n.


member of a pair of homologous chromosomes

homologous chromosomes

identical pairs of chromosomes that are formed during synapsis of meiosis I in diploid organisms

independent assortment

random distribution of homologous chromosome pairs of genes on different chromosomes to the gametes during meiosis


failure of chromosomes or chromatids to separate during anaphase I or II of meiosis, resulting in an uneven distribution of genetic material


separation of the genes of one parent from that of the other during gamete formation

sexual reproduction

form of reproduction that involves fusion of gametes, producing offspring that differ genetically from either parent

sister chromatid

identical half of a replicated chromosome that is still attached at the centromere

somatic cell

any cell in the body of a multicellular organism that is not a germ-line cell