Lecture 8: Chromosome Abberations Flashcards
Phenotypic variations result from changes of what?
Individual genes
What are the 4 types of Chromosome mutations and aberrations?
- Total number of chromosomes vary
- Deletions
- Duplications
- Rearrangements
Define Aneuploidy
- Variations in chromosome number
- Organisms GAIINS or LOSES one or more chromosomes (NOT ENTIRE SET)
Define Monosomy
Loss of single chromosome in diploid genome
Define Trisomy
- Gain of single chromosome
- Ex.)Trisomy-21 Down Syndrome
Define Euploid
Complete haploid sets of chromosomes are present
Define Polyploidy
More than two sets of chromosomes are present
Define Triploid
Three sets of chromosomes
Define Nondisjunction
- Gives rise to chromosomal variation
- Paired homologs fail to disjoin during segregation
- Nondisjunction during meiosis 1 or 2
Define Haploinsufficiency
When one copy is NOT sufficient for organism to survive
Define Monosomy
- Loss of one chromosome
- Produces 2n − 1 complement
- Although one copy remains, if copy is
lethal, organism is not viable - Monosomy unmasks recessive
lethals - Haploinsufficiency: When one copy
is not sufficient for organism to
survive
Define Trisomy
- 2n + 1 chromosomes
- Addition of chromosome produces
more viable organisms - Trisomies for autosomes are often
lethal - Plant trisomies are viable
- Phenotype altered
- Example: Datura stramonium with
altered phenotype
Define Deletions
- Missing regions of chromosome
- Chromosome breaks in one or more places
- Portion is lost
Location of deletion can vary. Provide 2 examples
- Terminal deletion (near one end)
- Intercalary deletion (interior of the chromosome)
Understand Compensation Loop and Buckling Out
- Synapsis between chromosomes with larger intercalary deletion and normal complete homolog
- Requires unpaired region of normal homolog to loop out of linear structure into deletion or compensation loop
Define Duplications
- Repeated segment of chromosome
- Single locus is present more than once in genome
- Can produce compensation loop
- Arise from unequal crossing over between synapsed chromosomes during meiosis
Gene Duplication may play a role in evolution. Provide an example/understand this!
- Gene duplication hypothesized to be a major source of new genes
- Hypothesis supported by discovery of genes with substantial amount of DNA sequence in common, but distinct gene products
- Example: Genes encoding digestive enzymes trypsin (active form) and
chymotrypsin (apoenzyme)
Define Extranuclear inheritance
- Transmission of genetic information to offspring through cytoplasm NOT nucleus
- Usually from one parent
Define Varieties in extranuclear Inheritance
- Organelle heredity
- Infectious heredity (i.e. viruses and send that info to offspring)
- Maternal effect
Explain mtDNA: Mitochondrial DNA
- Exists in eukaryotes as double-stranded circular DNA
- Smaller than DNA in chloroplasts
- SMALLLLLER than normal DNA
Explain cpDNA: Chloroplast DNA
Genes encode products involved in photosynthesis and translation
Nuclear genes encode majority of proteins for mitochondrial function. Provide 4 examples!
- DNA and RNA polymerase
- Initiation and elongation factors
- Ribosomal proteins
- Aminoacyl tRNA synthetases
How is mtDNA susceptible to mutations
- No structural protection from histones
- DNA repair mechanism limited
- High concentrations of ROS (reactive oxygen species)
generated by cell respiration - ROS is toxic—damages organelle contents (proteins,
lipids, mtDNA)
Provide 3 disorders arising from mtDNA
- MERRF (myoclonic epilepsy and ragged-red fiber disease)
- LHON (Leber’s hereditary optic neuropathy)
- KSS (Kearns–Sayre syndrome)
What are a few examples of Mitochondrial dysfunction implicated in most human
diseases
- Anemia
- Blindness
- Type II diabetes
- Autism
- Infertility
- Neurodegenerative diseases: Parkinson and Alzheimer
Explain Down syndrome
- Trisomy of chromosome 21
- Has 12-14 characteristics
- On average affected individuals express 6 to 8 characteristics
Explain Down Syndrome Critical Region
- Critical region of chromosome 21
- Genes are dosage sensitive
- Responsible for many phenotypic-associated syndrome
What is the origin of extra 21st chromosome
- Nondisjunction of chromosome 21 during meiosis
- Homologs do not disjoin in anaphase 1 or 2
- Leads to n+1 gametes
- Ovum is the source of 95% of trisomy cases
- INCREASED INCIDENCE WITH INCREASING MATERNAL AGE
Provide 2 examples of Diagnostic testing
- Amniocentesis or chorionic villus sampling (CVS)
* Fetal cells obtained from the amniotic fluid or chorion of the placenta - NIPGD: Noninvasive prenatal genetic diagnosis
* Fetal cells and DNA obtained from maternal circulation
Provide 2 examples of Human Aneuploidy
- Patau syndrome (trisomy 13)
- Edwards syndrome (trisomy 18)
*Note: Both trisomies survive to term, but manifest severe malformations and early lethality
Define Polyploidy and provide a few examples.
- Polyploidy: More than 2 multiples of haploid chromosomes found
- Ex: Triploid (3n), Tetraploid (4n), and Pentaploid (5n)
Define Autoploidy
Addition of one or more sets of chromosomes identical to the haploid complement of same species
Define Allopolyploidy
Combination of chromosome sets from different species as a
consequence of hybridization
What are some examples of Chromosome rearrangements
- Deletions
- Duplications
- Inversions
- Nonreciprocal translocations
- Reciprocal translocations
Define Deletions
- Missing regions of chromosome
- Chromosome breaks in one or more places
- Portion is lost
Deletions can vary on the location. Provide 2 locations!
- Terminal deletion (near one end)
- Intercalary deletion (interior of the chromosome)
Explain Buckling Out/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
