MT6315 CHROMOSOMAL ALTERATIONS Flashcards
Chromosomal mutations are commonly known as?
chromosomal aberrations
Chromosomal mutations are variations from?
Wild type phenotype in chromosome structure or number
How do chromosomal mutations arise?
Spontaneously or induced by chemical or radiation mutagens.
Abnormal chromosomal number refers to?
Aneuploidy
Chromosomal alteration refers to?
Structural abnormality
Chromosomal abnormalities are influenced by?
Genomic imprinting
Mitochondrial inheritance
Expansion of trinucleotide repeats
Types of Chromosomal mutations based on Variation in Chromosome Structure
- Deletion
- Duplication
- Inversion
- Translocation
Types of Chromosomal mutations based on Variation in Chromosome Number
- Aneuploidy (Monosomics/Trisomics/Nullisomics/Tetrasomics)
- Polyploidy
3 broad categories of chromosome mutations?
Chromosome rearrangements
Aneuploidy
Polyploidy
one or more individual chromosome pair has its number altered
Aneuploidy
overall chromosome number is unaffected, but large pieces are moved
Chromosome rearrangement
one or more complete chromosome sets are added
Polyploidy
Chromosomal aberrations are most often caused by?
errors during cell division.
Aneuploidy may result in errors occurring in?
meiosis.
Most common aneuploidy error is?
nondisjunction, when a set of chromosomes do not properly separate, which leaves one or two sex cells with an extra chromosome or with one less chromosome.
chromosomes has failed to separate or segregate at
anaphase so that both chromosomes of the pair pass
to the same daughter cell.
Nondisjunction
Nondisjunction is common in?
commonly in meiosis, but it may occur in mitosis to produce a mosaic individual.
When is nondisjunction common in mitosis?
to produce a mosaic individual.
Structural chromosomal aberrations can result in?
Aneuploidy
Kinds of Structural chromosomal aberrations?
Deletion
Inversion
Duplication
Translocation
Chromosomal disorders are sometimes caused by?
Mosaicism
What is mosaicism?
Two or more different cell lines in one person.
Can occur after nondisjunction in meiosis during early embryonic development.
This results in one line of cells with a chromosomal aberration while other lines may stay unchanged.
Mutation that results in the doubling of a segment of a chromosome.
Duplication
Forms of duplication?
Tandem duplication
Reverse duplication
Terminal tandem duplication
Misplaced Duplication
The International System for Human Cytogenomic Nomenclature (ISCN) for duplication?
dup
dup(17p12)
Charcot–Marie–Tooth disease type 1A.
What type of duplication: one right after the other
Tandem
What type of duplication: duplicated region is inverted
Reverse duplication
T or F: Individuals can ONLY be homozygous for duplication
F, both hetero and homo
In heterozygous individuals for duplication, when do problems arise?
Prophase I of meiosis and synapsis
What does the duplicated chromosome need to do in order to let the synapsis occur?
Loop out
Duplications have an effect on an individual’s ____, due to ______.
Phenotype
Unbalanced Gene Dosage
Good side of duplication?
Contributed to evolution through new genes being “born” with novel functions
What is an example of evolution through duplication?
Fetal hemoglobin which allowed for in utero reproduction
loss of a segment of a chromosome.
Deletion
Where does deletion start?
breaks of chromosomes
What causes breaks of chromosomes?
agents (such as heat, ionizing radiation, viruses, transposable elements) or by errors in recombination.
What is pseudo dominance?
Dominant ‘A’ allele is deleted, causing the expression of the recessive ‘a’ allele
Types of deletions?
Terminal deletion
Intercalary/interstitial deletion
Microdeletion
a deletion that occurs from the interior of a chromosome.
Intercalary/interstitial deletion
a deletion that occurs towards the end of a chromosome.
Terminal deletion
a relatively small amount of deletion usually found in children with physical abnormalities
Microdeletion
Sizes of micro deletions?
up to 5Mb mutations that could include a dozen genes
Where is micro deletion usually found?
in children with physical abnormalities. A large amount of deletion would result in immediate abortion (miscarriage)
If a deletion is large enough it can be detected where?
Karyotype
T or F: Deletions also have looping out in Prophase I to allow for the alignment of synapse
T
The effect of deletion depends on?
The genetic information deleted (some are lethal, some are asymptomatic)
If the deleted chromosome includes the centromere, the chromosome (will/will not) segregate during mitosis or meiosis.
will NOT, will be lost during cell division
When are deletions detrimental to an individual?
when HOMOZYGOUS due to the complete absence of that genetic information
What happens in a heterozygous individuals for deletion?
Gene imbalance
T or F: Recessive alleles appear more readily in deletions
T because there are no other alleles to mask
Human syndromes related to deletion are (common/rare).
Rare
The International System for Human Cytogenomic Nomenclature (ISCN) for deletion?
Abbreviations include a minus sign (-) for chromosome deletions, and del for deletions of parts of a chromosome.
Deletion of a number of pairs that is not evenly divisible by three will lead to?
frameshift mutation
Frameshift mutation causes?
Causing all of the codons occurring after the deletion to be read incorrectly during translation, producing a severely altered and potentially nonfunctional protein.
deletion that is evenly divisible by three is called?
in-frame deletion.
Deletions are responsible for an array of genetic disorders, including?
some cases of male infertility, 2/3 of cases of Duchenne muscular dystrophy, and 2/3 of cases of cystic fibrosis (those caused by ΔF508).
Deletions in the SMN-encoding gene cause?
spinal muscular atrophy, the most common genetic cause of infant death.
Microdeletions are associated with many different conditions, including?
Angelman Syndrome, Prader-Willi Syndrome, and DiGeorge Syndrome
Some syndromes are associated with both microdeletions and genomic imprinting such as?
Angelman syndrome and Prader-Willi syndrome
What is genomic imprinting?
Same microdeletion can cause two different syndromes depending on which parent the deletion came from.
5p-
Cri du chat syndrome
11q-
Wilms tumor
13q-
Retinoblastoma
15q-
Prader-Willi syndrome
Cancer of the eye, increased risk of other cancers
Retinoblastoma
Infants: weak slow growth; children and adults: obesity, compulsive eating
Prader-Willi syndrome
Infants have catlike cry, some facial anomalies, severe mental retardation
Cri du chat syndrome
This condition occurs in every 1 out of 100,000 births.
Mentally retarded, with defects on facial development, gastrointestinal malformations, and abnormal throat structures.
Cri du chat syndrome
del15q11 or q13
Prader-Willi Syndrome
Often smile and laugh frequently, and have happy, excitable personalities.
Developmental delays, which begin between about 6 and 12 months of age, are usually the first signs.
Seizures may begin between the ages of 2 and 3 years old.
Angelman Syndrome
The ____ gene is located on the segment of chromosome 15 that is often deleted in people with Angelman syndrome.
OCA2
Results when a segment of a chromosome is excised and then reintegrated in an orientation 180 degrees from the original orientation.
Inversion
Forms of Inversion?
Pericentric Inversion
Paracenric Inversion
The International System for Human Cytogenomic Nomenclature (ISCN) for inversion?
inv
Type of inversion: does not include the centromere
Paracentric
Type of inversion: includes the centromere
Pericentric
T or F: Inversions played a role in human evolution
T
Karyotypic differences between humans and chimpanzees include how many pericentric inversions?
9
What is a prerequisite for any assessment of the genetic consequences of these inversions?
Detailed analysis of the respective chromosomal breakpoints
The breakpoints of the inversion that distinguishes human chromosome 4 (HSA4) from its chimpanzee counterpart were identified by?
FISH
Comparative sequence analysis
These breakpoints, at _____ and ____, do not disrupt the protein coding region of a gene, although they occur in regions with an abundance of ____ and ____ elements
HSA4p14 and 4q21.3
LINE and LTR-elements.
When is a gene rendered inactive in inversion?
If an inversion breaks a gene in half and that half moves to another part of the chromosome
How are genes regulated on the chromosome?
by their position
Changing a gene’s position will lead to?
Changes in regulation
Position effect
In inversion, do genes require looping?
Yes
Intense looping in inversion causes?
Chromosomal damage and loss
change in position of chromosome segments and the gene sequences they contain
Translocation
Is there a presence of gains or losses in genetic material for translocation?
No
Kinds of Translocation?
Intrachromosomal
Interchromosomal