Chromosomes Flashcards
Describe the structure of a chromosome (after replication).
Two genetically identical sister chromatids
Joined at a centromere
Telomeres at the end of each chromatid
Heterochromatic and euchromatic sections
What is euchromatin?
Lightly packed form of chromatin
What is heterochromatin?
Tightly packed form of chromatin
Which form of chromatin does DNA transcription take place on?
Euchromatin
Loosely packed - allows enzymes n shit in
What are telomeres?
Long section of repeating base sequences at the ends of chromosomes
In mitosis, sections are cut off the 3’ to 5’ strand of DNA for reasons I can’t be bothered typing (end replication problem)
Telomeres protect useful DNA being cut off
Describe the phases of mitotic cell cycle.
G1 - cell grows
S - DNA replicates
G2 - Cell prepares to divide
M - mitosis - cell division
List the stages of mitosis.
Prophase Metaphase Anaphase Telophase Cytokenesis
(interphase)
What happens in Prophase?
Chromosomes condense
Nuclear membrane
Spindle fibres form from the centriole
What happens in metaphase?
Chromosomes align on equator of cell
Chromosomes attach to centrioles via spindle fibre
Maximum condensation of chromosomes
What happens in anaphase?
Sister chromatids split apart (centromere splits)
Sister chromatids move to opposite poles of the cell, along the spindle fibre
What happens in telophase?
New nuclear membranes form
What happens in cytokinesis?
Cytoplasm splits and two new daughter cells are formed
Cells are diploid, have 46 chromsomes and are genetically identical
What is the name given to repetitive sequences of DNA, like the ones found in centromeres and telomeres?
Satellite DNA
What is the kinetochore?
A complex of proteins associated with the centromere of a chromosome during cell division, to which the microtubules of the spindle attach
One forms per sister chromatid
What are the 2 types of tandemly repeated DNA sequences?
Satellite and minisatellite
What are the types of repeated interspersed DNA sequences?
SINEs - short interspersed nuclear elements
LINEs - long interspersed nuclear elements
Describe the properties and functions of histones.
Positively charged proteins
8 histones come together to form a core
DNA wraps around histone cores to form nucleosomes
Looks like beads on a string
Describe the levels of structure of chromatin.
1) DNA chain
2) Nucleosome
3) Chromatin fibre (further wrapping of nucleosomes)
4) Fibre scaffold complex
5) Chromosome
Why is it important that histone proteins are positively charged?
DNA is negatively charged
Neutralised by histones and holds it together
What are the 3 types of chromosome, and what are their differences?
Metacentric - p arm similar size to q arm
Submetacentric - p < q
Acrocentric - p «_space;q (p has no functional DNA)
What type of cell in the body can not be used for chromosome analysis and why?
Red blood cells
No nucleus so no chromosomes
Describe the process of chromosome analysis.
Blood taken and RBC’s seperated off
Add culture medium to white cell suspension
Incubate 3 days at 37 degrees
Add colchicine
Separate off white cells
Add hypotonic saline
Fix cells
Drop cells onto slide and stain
Analysis and photograph to produce karyotype
What does staining of chromosomes show?
G-bands
Why would you use fluorescent in sutu hybridisation (FISH)?
Highlight specific genes or specific parts of genes
What are the different types of FISH probes?
Unique sequence probes
Centromeric probes
Telomeric probes
Whole chromosome probes
Which type of FISH probe is good for determining chromosome number?
Centromeric probes
What type of cells undergo meiosis?
Germ cells
Diploid cells (in ovaries and testes) form haploid cells
How does meiosis create genetic diversity?
Crossing over (re-combination)
Independent assortment
What is Oogenesis?
Process of egg formation
Spermatogenesis is the process of?
Sperm formation
Out of sperm and eggs, which has more chance of mutation?
Sperm
More cell divisions so more chance of mutation
In females, ovulation takes place at birth.
Meiosis normally produces 4 daughter cells, but how is this different in women?
Meiosis II produces 1 Ootid and 3 polar bodies
Ootid differentiates into an egg
Polar bodies are degraded
What organelle is maternally inherited only?
Mitochondria (+ their DNA)
What are 3 types of chromosomal abnormalities?
Numerical
Structural
Mutational
What type of abnormality is associated with down’s, turner’s and patau syndromes?
Numerical abnormality
Aneuploidy - wrong number of chromosomes
Down's = Extra 21 Edward's = Extra 18 Patau = Extra 13
What gives rise to numerical chromosomal abnormalities?
Non-disjunction during meiosis
Trisomy is more commonly caused by what sex?
Maternal
Give some examples of sex chromosomes aneuploidy syndromes.
Turner syndrome - 45, X
Klinefelter syndrome - 47, XXY
What are the types of structural abnormalities of chromsomes?
Translocations
Deletions
Inversions
Insertions
What are the two types of translocations?
Robertsonian - fusion of two acrocentric chromosomes, with loss of the short arms (p arms)
Reciprocal - breaks of 2 chromosomes with the formation of 2 new chromosomes from these
How can reciprocal translocations be balanced or unbalanced?
If chromosome A and chromosome B translocate, part of B is on A and vice versa
If A and B end up in the same cell after meiosis, then the DNA compliment is the same, and the outcome will most likely be fine
If A and B end up in different daughter cells, then the zygotes will have an unbalanced amount of A or B
Partial trisomy + partial monosomy
What is the difference between terminal and interstitial deletion?
Terminal = deletion at ends
Interstitial = deletion in the actual chromosome (not the end)
What are the two types of inversion, and are the balanced/unbalanced?
Paracentric and pericentric
Paracentric = inversion in chromosome not involving centromere
Pericentric = inverted section contains centromere
Balanced rearrangement
What are the 2 types of genetic mutation?
Germline or somatic
What are the different types of coding mutations?
Silent - Base change with no effect on coded AA
Missense - Base change causing AA change
Nonsense - Base change causing stop codon
Frameshift - deletion/insertion of a base - codons after are read out of frame
What is the difference between transitions and transversions?
Transitions = purine to purine or pyrim. to pyrim.
Transversions = purine to pyrim. or pyrim. to purine
What are the ways that we can detect mutations?
PCR - Polymerase chain reactions
Gel electrophoresis
RFLP - Restriction fragment length polymorphism analysis
ARMS - Amplification refractory mutation system
DNA sequencing
Which mutation detection technique involves heating and DNA sample then adding nucleotides, repeatedly?
PCR
In gel electrophoresis, different DNA fragments are separated based on what feature?
Size
DNA fragment ‘bands’ can be compared to other bands to detect differences/mutations to the bands formed from non-mutated DNA fragments (controls)
What technique is most sensitive/accurate for detecting mutations?
DNA sequencing
What is the only lab procedure for DNA analysis that doesn’t involve using an electric field to separate DNA fragments?
PCR
