chromosome /chro·mo·some/ (kro´mah-sōm) in animal cells, a structure in the nucleus containing a linear thread of DNA which transmits genetic information and is associated with RNA and histones; during cell division the material composing the chromosome is compactly coiled, making it visible with appropriate staining and permitting its movement in the cell with minimal entanglement; each organism of a species is normally characterized by the same number of chromosomes in its somatic cells, 46 being the number normally present in humans, including the two (XX or XY) which determine the sex of the organism. In bacterial genetics, a closed circle of double-stranded DNA which contains the genetic material of the cell and is attached to the cell membrane; the bulk of this material forms a compact bacterial nucleus.chromoso´mal .jpg)
homologous chromosomes
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Chromosome. (A), Long, threadlike interphase chromatin in nucleus. (B), Giemsa-stained, partially condensed chromatid in late prophase. (C), Giemsa-stained, fully condensed chromatid in metaphase; note that some of the sub-bands visible in late prophase have condensed into single bands. (In B and C, only one of a pair of sister chromatids is shown.)
bivalent chromosome see bivalent (2).
homologous chromosomes a matching pair of chromosomes, one from each parent, with the same gene loci in the same order.
Ph1 chromosome , Philadelphia chromosome an abnormality of chromosome 22, characterized by shortening of its long arms (the missing portion probably translocated to chromosome 9); present in marrow cells of patients with chronic granulocytic leukemia.
ring chromosome a chromosome in which both ends have been lost (deletion) and the two broken ends have reunited to form a ring-shaped figure.
sex chromosomes those associated with sex determination, in mammals constituting an unequal pair, the X and the Y chromosome.
somatic chromosome autosome.
X chromosome a sex chromosome, carried by half the male gametes and all female gametes; female diploid cells have two X chromosomes.
Y chromosome a sex chromosome, carried by half the male gametes and none of the female gametes; male diploid cells have an X and a Y chromosome.
homologous chromosomes
Etymology: Gk, homos, same, chroma color, soma body
any two chromosomes in a diploid somatic cell that are identical in size, shape, and gene loci. In humans there are 22 pairs of homologous chromosomes and 1 pair of sex chromosomes, with 1 member of each pair derived from the mother and the other from the father.
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