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chromatid(krō`mətəd): see chromosomechromosome
, structural carrier of hereditary characteristics, found in the nucleus of every cell and so named for its readiness to absorb dyes. The term chromosome
..... Click the link for more information. ; crossing overcrossing over,
process in genetics by which the two chromosomes of a homologous pair exchange equal segments with each other. Crossing over occurs in the first division of meiosis. At that stage each chromosome has replicated into two strands called sister chromatids.
..... Click the link for more information. .
one of the components of a chromosome, formed in the nucleus during the interphase of the cell nucleus as a result of the chromosome’s duplication. In mitosis, each chromosome consists of two chromatids; after separating into the daughter nuclei, each chromatid becomes an independent chromosome. In meiosis, homologous chromosomes come together in pairs to make up a four-chromatid structure, or tetrad.
According to the single-chain chromosome model, each chromatid contains in cross section a single tightly coiled and condensed double-strand molecule of deoxyribonucleic acid (DNA). In the multichain chromosome model, it is assumed that each chromatid contains in cross section several DNA molecules, in which case various types of chromatids are distinguished, such as semichromatids and quarter-chromatids. Most experiments have confirmed the single-chain model.
I. I. KIKNADZE