Bs 50 Test 2

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Synteny

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Genes on the Same Chromosome

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metacentric chromosome

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chromosome wth its centromere in the middle - V shape, arms are equal length

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submetacentric chromosome

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a chromosome with a somewhat off-center centromere, J-shape

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acrocentric chromosome

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a chromosome with a centromere very close to one end - "I" Shaped

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acentric

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chromosome that lacks a centromere

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dicentric chromosome

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a chromosome with 2 centromeres

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dosage compensation

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a mechanism regulating x-linked genes such that their activies are equal in males and females; in mammals, random inactivation of one x chromosome in females results in equal amounts of the products of x-linked genes in males and females

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X inactivation

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in mammals, the genetic inactivation of all X chromosomes except one in each cell lineage, except the one in very early embryo

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barr body

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in certain female cells, a densely staining heterochromatic body in the nucleus of interphase cells observed in a microscope

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mosaic

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an individual that has cells of two or more different genotypes

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psuedoautosomal regions

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the regions of shared X-Y homology, where crossing-over regualarly occurs during spermatogenesis (PARp - short & PARq - long)

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transcription factor

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a protein that stimulates transcription of its target genes

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Testis-Determing Factor (TDF)

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the master sex-determining gene SRY, that triggers male embryonic development

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Trisomic

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an otherwise diploid organism that has an extra copy of an individual chromosome

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triploid

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three sets of chromosomes (69 in humans)

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tetraploid

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four sets of chromosomes (92 in humans)

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Euploid

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a cell or an organism having a chromosome number that is an exact multiple of the haploid number

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Aneuploid

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a cell or organism in which the chromosome number is not an exact multiple of the haploid number, more generally, aneuploidy is a condition where specific chromosomes or genes are present in fewer or extra copies

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balanced translocation

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a euploid condition in which nonhomologous chromosomes have an interchange of parts, but all parts are present

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unbalanced translocation

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an aneuploid condition in which some part of the genome is missing

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monosomy

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when an otherwise diploid organism is missing a copy of an individual chromosome

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Non-Fatal Trisomies

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Trisomy 13 (fetus alive for a few days)
Trisomy 18 (fetus alive for a few days)
Trisomy 21 (Down Syndrome)

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Down Syndrome (Down's Syndrome)

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Trisomy 21- usually caused by nondisjunction in oogenesis of eggs. Drastically increased chances of occurance in older mothers

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Trivalent

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structure formed by three homologous chromosomes in meiosis I in a triploid or trisomic chromosome when each homolog is paired along part of its length with the first one and then the ther of the homologs

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Trisomy-X Syndrome

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47,XXX - phenotypically female, usually rather normal

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Double-Y Syndrome

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47, XYY - male, tall, phenotypically and psychologically normal

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Kleinfelter Syndrome

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47, XXY - male, tall, sterile, mild mental impairment

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Turner Syndrome

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45, X - female, sterile, short

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deletion

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a segment of a chromosome that is missing

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duplication

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abnormal chromosomes that have a region that is present twice

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tandem duplication

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a chromosome where the duplicated segment is present in the same orientation immediately adjacent to teh normal region in the chromosome

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chimeric gene

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composite gene formed by the joining of two different parts of two genes

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inversion loop

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loop structure formed by synapsis of homologous genes in a pair of chromosomes, one of which contains an inversion

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paracentric inversion

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the inversion of a chromosome that does not include the centromere. The products of crossing over include a dicentric and an acentric chromosome

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pericentric inversion

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an inversion of a chromosome that contains the centromere. the products of pericentric inversion are both monocentric chromosomes

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translocation

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a chromosomal aberration resulting from the interchange of parts between nonhomologous chromosomes

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semi-sterility

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an organism that is heterozygous for a reciprocal translocation usually produces only about half as many offspring as normal

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adjacent-1,2 segregation

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type of segregation from a heterozygous reciprocal translocation in which a stucturally normal chromosome segregates with a translocated chromosome

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alternate segregation

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segregation from a heterozygous reciprocal translocation in which both pairs of the reciprocal translocation separate from both nontranslocated chromosomes in the first meiotic division

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autopolyploidy

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all chromosomes in the polyploid species derive froma single diploid ancestral species

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allopolyploid

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a polyploid formed from the hybridization of two different species