Genetics Exam 1
Terms
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- Chromosomes consist of how many arms? They are connected at the ____?
- Two arms (short = P, long = Q) connected at the centromere
- Three shapes according to the position of the centromere
- Centromere is: Metacentric (in the middle) Submetacentric (off-center) Acrocentric (near the end)
- Satellites
- Found on acrocentric chromosomes at the top end of the short arm. Satellite stalks contain multiple copies of genes coding for rRNA and are called the nucleolar organizing regions (NORs)
- Telomeres
- Ends of chromosomes
- sub-telomeric regions
- small portions just next to the telomeres
- How many chromatids do chromosomes have early in the cell cycle? How about after replication?
- 1 chromatid in early cell cycle, 2 sister chromatids after replication
- Number of chromosomes in the normal human somatic cell?
- 46 chromosomes, 23 matching pairs
- Homologs/Homologous chromosomes
- pair of chromosomes - one derived maternally and the other paternally
- # of Autosome pairs
- 22 - numbered from largest to smallest
- # of sex chromosome pairs
- 1 pair - XX or XY
- Karyotype
- conventional arrangement of metaphase chromosomes for analysis
- What are the most common karyotype samples
- To study individual's chromosomes: Blood lymphocytes fetus chromosomes: amniotic fluid or chorionic villi constitution of tumors: bone marrow, tumor tissue
- Phytohemagglutinin
- stimulates lymphocytes to divide
- Colcemide
- destroys mitotic spindle to accumulate cells at metaphase
- G-Banding
- AT-rich regions stain (G-dark bands) and GC rich regions do not stain (G-light bands)
- High-resolution banding/karyotype
- chromosomes are prepared in prometaphase because they are longer and increase the number of sub-bands seen
- Cytogenetic shorthand notation
- 1. Chromosome is divided into regions 2. regions are numbered in order from centromere towards the ends 3. regions are further subdivided 4. Total number of chromosomes is listed first, then the X-Y chromosome constitution, then... 5a. Nothing if normal 5b. additional information describing what's abnormal
- 47,XY,+21
- 47 total chromosomes, X and Y and extra 21 chromosome
- 45,XX,-22
- 45 total chromosomes, XX, missing 22 chromosome
- 46,XY,dup(7)(q11q31)
- 46 total chromosomes, XY, duplication on chromosome 7 from region q11 to q31
- 46,XY,del(22)(q11.2)
- 46 total chromosomes, XY, deletion on chromosome 22 in region q11.2
- Band level
- approximate degree of resolution of the study (400 bands minimal, higher end is 800-850 bands)
- Molecular cytogenetics
- DNA probe is used to detect presence or absence of a specific chromosomal segment. Can detect in both dividing and non-dividing cells
- FISH
- fluorescence in situ hybridization: identification of specific chromosomes and parts of chromosomes by in situ hybridization with labeled DNA probes
- FISH uses
- 1. detecting submicroscopic deletions and duplications 2. detecting subtle chromosome rearrangements 3. identifying marker chromosomes 4. identifying the content of multiple rearranged chromosomes 5. detecting aneuploidy (extra or missing chormosomes) in interphase cells in cancers
- Satellite repeat-sequence probes
- FISH probe type: - target only the centromeres of specific chromosomes - useful in determining the number of chromosomes in cases of possible aneuploidy or in cancer cells - can use with interphase cells if metaphase cells are not available - can monitor the proportion of XX and XY cells following a bone marrow transplant from a donor of the opposite sex
- Whole chromosome paint probes
- FISH probe type: - Cover an entire chromosome - Helpful for identifying the chromosomal identity of marker chromosomes and of material translocated from one chromosome to another
- Unique sequence probes
- FISH probe type: - target a specific locus or gene on a chromosome - use for diagnosis of chromosome microdeletion syndromes - certain acquired translocations that are unique to specific cancers can be detected in interphase cancer cells
- Telomeres
- physical ends of chromosomes comprised of specialized nucleoprotein complexes that serve primarily in the protection, replication, and stabilization of chromosome ends. SAME sequence at ends of human chromosomes TTAGGG
- Subtelomere
- lies proximal to the telomere sequence with unique DNA sequences. Significant portion of individuals with intellectual disabilities show a significant proportion of unbalanced abnormalities involving the telomeres. These abnromalities are familial in 50% of cases
- Array-based comparative genomic hybridization (array CGH/arr CGH/chromosomal microarray analysis)
- High-res tech. used to detect sumicroscopic chromosomal duplications and deletions - comprises hundreds to thousands of FISH tests done at one time on a single slide
- copy number
- how many copies of a given clne are present in the test DNA
- copy number variation
- segment of extra or missing DNA detected by microarray analysis
- Normal copy number variation
- Ratio of 1:1 with reference DNA in microarray
- Duplications in copy number variation
- Ratio of 1.5:1 with reference DNA in microarray
- Deletions in copy number variation
- Ratio of 0.5:1 with reference DNA in microarray
- BAC array
- 0.5-1Mb detection