Chapter 3 - The Chromosomal Basis Of Inheritance

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Chromosome theory of heredity

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a unifying theory stating that inheritance patterns may be generally explained by assuming that genes are located in specific sites on chromosomes

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Nondisjunction

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the failure of homologs (at meiosis) or sister chromatids (at mitosis) to separate properly to opposite poles

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Haploid

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a cell having one chromosome set or an organism composed of such cells

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Diploid

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a cell having two chromosome sets or an individual organism having two chromosome sets in each of its cells

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Heterochromatin

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densely staining condensed chromosomal regions, believed to be for the most part genetically inert

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Euchromatin

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a chromosomal region that stains normally; thought to contain the normally functioning genes

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Telocentric

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a chromosome having the centromere at one end

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Acrocentric

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a chromosome having the centromere located slightly nearer one end than the other

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Metacentric

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a chromosome having its centromere in the center

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Satellite DNA

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any type of highly repetitive DNA; formerly defined as DNA forming a satellite band after cesium chloride density-gradient centrifugation

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Nucleolar organizers (NO)

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a region (or regions) of the chromosome set that is physically associated with the nucleolus and contains rRNA genes

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Chromosome bands

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transverse stripes on the chromosomes of many organisms, revealed by special staining procedures

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Polytene chromosomes

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a giant chromsome in specific tissues of some insects, produced by an endomitotic process in which the multiple DNA sets remain bound in a haploid number of chromosomes

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Chromocenter

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the point at which the polytene chromosomes appear to be attached together

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Bands

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transverse stripes on chromosomes revealed by various stains

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FISH (fluorescence in situ hybridization)

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in situ hybridization with the use of a probe coupled with a fluorescent molecule

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Nucleosomes

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the basic unit of eukaryotic chromosome structure; a ball of eight histone molecules that is wrapped by two coils of DNA

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Histones

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a type of basic protein that forms the unit around which DNA is coiled in the nucleosomes of eukaryotic chromosomes

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Solenoid structure

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the supercoiled arrangement of DNA in eukaryotic nuclear chromosomes that is produced by coiling of the continuous string of nucleosomes

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Scaffold

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the central framework of a chromosome to which DNA solenoid is attached as loops; composed largely of topoisomerase

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Scaffold attachment region (SAR)

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positions along DNA at which the DNA is anchored to the central scaffold of the chromosome

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mtDNA

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mitochondrial DNA

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Cytohet

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a cell containing two genetically distinct types of a specific organelle

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Cytoplasmic segregation

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segregation in which genetically different daughter cells arise from a progenitor that is a cytohet

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Mitosis

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a type of nuclear division (occuring at cell division) that produces two daughter nuclei identical with the parent nucleus

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Dyads

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a pair of sister chromatids joined at the centromere, as in the first division of meiosis

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Bivalents

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two homologous chromosomes paired at meiosis

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Sister chromatids

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the juxtaposed pair of chromatids arising from replication of a chromosome

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Tetrad

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four homologous chromatids in a bundle in the first meiotic prophase and metaphse

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Synaptonemal complexes

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a complex structure that unites homologs during prophase of meiosis

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Crossing over

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the exchange of corresponding chromosome parts between homologs by breakage and reunion

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Nuclear Spindle

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the set of microtubules that forms between the poles of a cell during nuclear division; the function of the nuclear spindle is to segregate the chromosomes or chromatids to the poles

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Kinetochore

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a complex of proteins to which a nuclear spindle fiber attaches

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Chiasma

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a cross-shaped structure commonly observed between nonsister chromatids in meiosis;
the site of crossing over

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Daughter cells

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two identical cells formed by the asexual division of a cell

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Meoisis

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two successive nuclear divisions (with corresponding cell divisions) that produce gametes that have one-half of the genetic material of the original cell

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Meiocytes

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cell in which meiosis takes place

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Gametes

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a specialized haploid cell that fuses with a gamete of the opposite sex or mating type to form a diploid zygote