Exam 2: Chromosome Abnormalities Flashcards
Define a mutation
A mutation is a change in genome nucleotide sequence that deviates from the norm.
-Allelic variation is generated via mutation
–Phenotypic variations result from changes in individual genes due to allelic variation
At what phase of mitosis are karyotypes typically done?
Metaphase
Define aneuploidy
Change in the number of individual chromosomes due to a addition or loss (no longer a balanced set)
What are the kinds of aneuploidy?
Nullisomy: Loss of both members of a homologous pair
2n-2
Monsomy: Loss of one member of a homologous pair
2n-1
Trisomy: Gain of one chromosome, resulting in 3 homologous pairs
2n+1
Tetrasomy: Gain of two chromosomes
2n+2
Discuss the use and limitations of karyotyping to identify chromosome abnormalities.
Use: Karyotyping is a test to examine chromosomes in a sample of cells. This test can help identify genetic problems as the cause of a disorder or disease.
Limitations: Karyotyping could miss small chromosomal mutations such as small structural abnormality like a a 5bp inversion.
Describe the relationship between nondisjuction and eu- or aneuploidy.
Nondisjunction is the most common mechanism resulting in aneuploidy. Nondisjunction is an error in which there is unequal distribution of the members of a single chromosome pair in cell division.
Describe advantages and disadvantages of chromosomal abnormalities.
Mutations are neither positive nor negative. Mutations can cause disease or death. However, some mutations have given species advantages that lead to speciation.
Define autoployploidy, allopolyploidy, and endoployploidy
Autopolyploidy: Addition of one or more sets of chromosomes identical to haploid complement of same species (ex: all human)
Allopolyploidy: Combination of chromosome sets from different species as consequence of hybridization (ex: mule– different homologous chromosomes, from horse and one from donkey)
Endopolyploidy: Condition where only certain cells in diploid organism are polyploid. Set of chromosomes replicates repeatedly without cytokinesis (endoreplication)
Define euploidy/polyploidy
Addition of complete chromosome set
What are the different of structural chromosomal rearrangements?
-Deletion
-Insertion
-Inversion
-Nonreciprocal translocations
-Reciprocal translocations
A diploid organism with only 1 chromosome has
Monosomy
A haploid organism with 2 chromosomes has
Disomy–which is abnormal here
Define nondisjunction
The failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.
Jimsom weed nondisjunction (Trisomy: 2n+1) is an example of a ________ chromosomal abnormality
positive
Trisomy of chromosome 21 causes
Down syndrome
Trivalent vs Bivalent & Univalent
Three copies of chromosome are synapsed
vs
Prior to first meiotic division, one bivalent and one univalent (an unpaired chromosome) may be present instead of a trivalent
Do duplications and/or deletions always cause gene dosage problems?
For some genes, having an extra copy may not cause any detectable problems.
For others though, it can upset the carefully regulated interactions tons inside the cell.
Deletions
Missing regions of chromosome where chromosome breaks in one or more places.
-Terminal deletion (near one end)
–Intercalary deletion (interior of the
chromosome)
Compensation Loop
Synapsis between chromosome with large intercalary deletion and normal complete homolog requires unpaired region of normal homolog to loop out of linear structure into deletion or compensation loop.
Be able to draw this
Duplications
Repeated segment of chromosome
Single locus is present more than once in genome
Arise from unequal crossing over between synapsed chromosomes during meiosis
Lead to the production compensation loops
Is the compensation group on the normal or abnormal chromosomes for deletions vs duplications?
Deletions– normal
Duplications– abnormal
What supports the theory that gene duplication plays a role in evolution?
Hypothesis supported by discovery of genes with substantial DNA sequence in common, but distinct gene products
Example: digestive enzymes trypsin and chymotrypsin
Inversions
-Rearrangement of linear gene sequence
-No loss of genetic information
-Segment of chromosome turned 180° within chromosome
-Requires two breaks in chromosome, and reinsertion inverted segment
-May arise from chromosomal looping
Paracentric vs Pericentric Inversion
Paracentric: Does not change lengths
of two arms of the chromosome. Centromere not part of inverted segment.
Pericentric: Centromere is part of inverted segment. Does change lengths of two arms of chromosome.
Do inverted and non inverted chromosomes pair in meiosis?
Yes but onlyyy if they form an inversion loop
Translocation
Movement of a chromosome segment to a non homologous chromosome or to another region of the same chromosome.
Nonreciprocal- no exchange
Reciprocal- exchange between segment
Segregation Patterns After a Reciprocal Translocation
Alternate segregation
-Segregation pattern at first meiotic
division
-Has complete complement of genetic information
Adjacent segregation
-Leads to gametes containing
duplications and deficiencies
Robertsonian Translocation
Involves breaks at extreme
ends of short arms of two nonhomologous acrocentric chromosomes
Large submetacentric or
metacentric chromosome
produced
Ex: Familial Down syndrome
Be able to draw out process
Fragile Sites
More susceptible to chromosome breakage when cultured in absence of folic acid or other chemicals
Sites indicate regions of non-tightly coiled chromatin
Fragile-X Syndrome
CGG repeat near to the gene FMR-1 (fragile-X mental retardation 1)
may cause the gene to be turned off as the size of the repeat increases.
