Chapter 6: Chromosomal Aberrations Flashcards
Alteration of the genetic material at the chromosomal level.
Chromosome mutation
An organism gains or loses one or more chromosomes but not a complete set.
Aneuploidy
What causes aneuploidy in organisms?
Nondisjunction
Paired homologs fail to disjoin during segregation causing an additional copy of chromosome upon fertilization.
Nondisjunction
Loss of a single chromosome from an otherwise diploid genome.
Monosomy
A phenomenon where a single copy of a recessive gene due to monosomy may be insufficient to provide a life-sustaining function for the organism.
Haploinsufficiency
Discuss the consequences of monosomy.
- Recessive lethal genes is unmasked and expressed
2. A single copy of the recessive gene may be insufficient to provide life-sustaining function.
Gain of a single chromosome in addition to an otherwise diploid genome.
Trisomy
True or False. Trisomic individuals in plants are not viable.
False. Trisomic plants may be viable just like the case of Datura and Oryza sativa
Designated as 47, 21+
Down syndrome (Trisomy 21)
Individuals with Down syndrome bear a striking resemblance to one another due to what structures?
- prominent epicanthic fold in each eye
2. Flat face and round head
What region in chromosome 21 contains the genes that are dosage-sensitive in this trisomy and responsible for the many phenotypes associated with the syndrome?
Down Syndrome Critical Region (DSCR)
True or False. Down syndrome individuals have an increased risk of developing a number of cancers involving solid tumors, including lung cancer and melanoma.
False. Decreased risk due to an extra copy of DSCR1 gene which encodes a protein that suppresses vascular endothelial growth factor (VEGF) leading to suppression of angiogenesis.
What gene do down syndrome individuals have in extra that lowers their risk of cancer?
DSCR1 gene
What does DSCR1 gene encodes?
A protein that suppresses the gene vascular endothelial growth factor (VEGF)
About 75 percent of nondisjunction leading to down syndrome occurs as?
First division nondisjunction
True or False. The spermatogonium is the source of the extra chromosome in about 95 percent of 47, 21+.
False. Ovum is the main source.
Pre-natal diagnostic technique where fetal cells are obtained from the amniotic fluid.
Amniocentesis
Pre-natal diagnostic technique where fetal cells are obtained from the chorion of the placenta.
Chorionic villus sampling (CVS)
An occurrence where complete haploid sets of chromosomes are present in addition to an otherwise haploid set.
Euploidy
A type of euploidy where more than two sets are present
Polyploidy
A type of polyploidy where each additional set of chromosomes is identical to the parent species.
Autopolyploidy
True or False. Autopolyploids are larger than their diploid relatives. This increase seems to be due to larger cell number rather than greater cell size.
False. It is due to increased cell size.
Two ways to induce autotriploidy.
- Two sperms fertilizing one ovum
2. Experimentally produced by crossing a diploid organism (haploid gamete) with a tetraploid organism (diploid gamete)
A failure of all chromosomes to segregate during meiotic divisions produces a haploid gamete. It is then fertilized by a normal haploid gamete. This produces an?
Autotriploid
Chromosomes have replicated, but the parent cell never divides and instead reenters interphase. This produces what?
Autotetraploid
Autotetraploid may be induced experimentally by:
- Applying cold or heat shock to meiotic cells.
2. Applying colchicine to somatic cells undergoing mitosis.
Explain how ploidy increases cell size.
Two genes that encode G1 cyclins are repressed when ploidy increases. This causes the cell to stay in G1 phase longer and, on average grows to a larger size before it moves beyond the G1 stage.
Polyploidy may also result from hybridizing two closely related species. This phenomenon is called?
Allopolyploidy
Allopolyploids contain the equivalent of how many haploid genomes.
Four haploid genomes derived from separate species.
If the aberration is found in one homolog but not the other, the individual is said to be?
Heterozygous for the aberration
Exchanges and transfers of genetic material are called?
Translocation
When a chromosome break in one or more places and a portion of it is lost, the missing piece is called a?
Deletion
A deletion that occurs at the end of the chromosome is called?
Terminal deletion
A deletion that occurs within the interior of the chromosome is called?
Intercalary deletion
For synapsis to occur between a chromosome with a large intercalary deletion and a normal homolog, the unpaired region of the normal homolog must “buckle out” into a?
Deletion loop
Results from the deletion of a small terminal portion of chromosome 5.
Cri du Chat Syndrome
Designated as 46, 5p-
Cri du Chat Syndrome
Two mechanisms of duplication
- unequal crossing over between synapsed chromosomes during meiosis
- Through a replication error prior to meiosis.
Multiple copies of genes are present to compensate with the demand of the gene product.
Gene Redundancy
Gene redundancy is most particular in?
rRNA genes
Determination of the percentage of the genome that codes for specific RNA sequence.
Molecular hybridization
True or False. One copy of the region designated as 16A is present on both X chromosomes of wild-type flies but that this region was duplicated in Bar flies and triplicated in double Bar flies.
True
Variations in the number of copies of certain genes are called?
Copy number variants
Portion of the chromosome that is missing in individuals with cri du chat contains what gene?
TERT gene
TERT gene encodes what specific enzyme?
telomerase reverse transcriptase
TERT gene encodes what specific enzyme?
telomerase reverse transcriptase
An enzyme essential for the maintenance of telomeres during DNA replication.
telomerase reverse transcriptase
This theory argues that over time the duplicate gene will accumulate mutation and become a gene on its own.
Evolution by Gene Duplication
Groups of contiguous genes whose products perform the same, or very similar functions.
Gene families
Cite an example of a gene family and relate it to evolution by gene duplication.
SRGAP2 genes are a gene family having four variants that being associated with the formation dendritic spines in the brain, which is believed to contribute to the evolution of expanded brain function in humans, including the development of language and social cognition.
Formation of what structure believed to contribute to the evolution of expanded brain function in humans
Dendritic spine in the brain
A type of chromosomal aberration in which a segment of a chromosome is turned around 180 degrees within a chromosome.
Inversion
True or False. An inversion does not involve a loss of genetic information but simply rearranges the linear gene sequence.
True
Type of inversion where the centromere is not part of the rearranged chromosome segment.
Paracentric
Type of inversion where the centromere is part of the inverted segment
Pericentric inversion
Organisms with one inverted chromosome and one noninverted homolog.
Inversion heterozygotes
Inversion heterozygotes can undergo normal linear synapsis.
False.
To undergo crossing over, the chromosome that contains the inverted region has to buckle out what structure?
Inversion loop
What products are made if crossing over does not occur within the inverted segment of the inversion loop?
- two normal chromatids
2. two inverted chromatids
What products are made if crossing over occurs within a paracentric inversion?
- one recombinant dicentric chromatid with insertion and deletion
- one recombinant acentric chromatid with insertion and deletion
- one non-recombinant normal sequence
- one non-recombinant inverted sequence
During anaphase, what happens to the acentric chromatid produced by a paracentric inversion?
An acentric chromatid moves randomly to one pole or the other or may be lost.
During anaphase, what happens to the dicentric chromatid produced by a paracentric inversion?
Dicentric chromatid is pulled in two directions.
True of False. In inversion heterozygotes, the inversion has the effect of suppressing the recovery of crossover products when chromosome exchange occurs within the inverted region.
True.
True of False. Up to one-half of the viable gametes have the inverted chromosome, and the inversion will be perpetuated within the species.
True.
Movement of a chromosomal segment to a new location in the genome.
Translocation
Involves the exchange of segments between two nonhomologous chromosomes.
Reciprocal translocation
If the translocation involves the internal chromosome segments, how many breaks are required?
Four. 2 on each non nonhomologous chromosome.
If the translocation involves the external chromosome segments, how many breaks are required?
- one on each nonhomologous chromosome.
Homologs that are heterozygous for a reciprocal translocation undergo what type of synapsis during meiosis?
Unorthodox synapsis
As few as 50 percent of the progeny survive.
Semisterility
One common type of translocation involves breaks at the extreme ends of the short arms of two nonhomologous acrocentric chromosomes. These small segments are lost, and the larger segments fuse at their centromeric region.
Robertsonian translocation
This type of translocation produces a new, large submetacentric or metacentric chromosome
Robeartsonian translocation
Specific areas along the chromosomes that fail to stain, giving the appearance of a gap.
Fragile sites
The most common form of inherited mental retardation.
Fragile X syndrome
Gene that spans the fragile site and is responsible for the syndrome.
Fragile X mental retardation 1 (FMR1 gene)
An untranslated area in the FMR1 gene adjacent to the coding sequence of the gene.
Upstream region
An epigenetic process that inactivates the gene.
Methylation
Normal product of the FMR1 gene.
Fragile X mental retardation protein (FMRP)
Normal individuals have between how many CGG trinucleotide repeats in their FMR1 gene?
6-54 repeats
Those with 55 to 230 repeats are considered?
Carriers of the Fragile-X syndrome
Carrier individuals with 55 to 230 repeats, though not at risk to develop the syndrome, may transmit to their offspring a gene with an increased number of repeats. This cycle continues until a syndromic threshold is reached. This is an illustration of what phenomenon?
Genetic anticipation
True or False. Genes such as FHIT that are located within fragile regions
undoubtedly have an increased susceptibility to mutations
and deletions.
True
Often altered or missing in cells taken from tumors of individuals with lung cancer.
Fragile Histidine triad gene
Which site is Fragile Histidine triad gene located?
FRA3B fragile site on the p arm of chromosome 3
Found to be either lost or genetically silenced in the large majority of lung tumors, as well as in cancer tissue of the breast, ovary, prostate, bladder, esophagus, and pancreas.
WW Domain Containing Oxidoreductase
Where does WW Domain Containing Oxidoreductase located?
Found within the FRA16D site on chromosome 16
