Chromosomes and cell division Flashcards
What is the telomere?
5’-TTAGGG-3’ repeats on the end of the chromosomes to protect them
What is the centromere?
Constricted region of repeating DNA joining sister chromatids together
Site of kinetochore
What are the stages of the cell cycle and what happens in each?
G1- growth
S- DNA synthesis
G2- cell prepaid for mitosis
M- mitosis
What are the stages of mitosis and what happens in each?
Prophase- chromosomes condense, nuclear membrane disappears, spindle fibres form
Metaphase- chromosomes align at centre of cell and spindle fibres attach
Anaphase- Sister chromatids separate longitudinally and move to opposite poles of the cell
Telophase- new nuclear membrane forms
Cytokinesis- Cytoplasm separates
What is the kinetochore?
Protein complex that binds to the microtubules and is required for chromosomes
What is heretochromatin?
Condensed, usually inactive form of DNA
What is euchromatin?
Open, usually active genes
What are extragenic sequences?
Tandemly repeated DNA sequences making up roughly 45%of the genome
What is a nucleosome?
146 base pairs wrapped around 8 histone proteins
What is the charge of DNA and histone?
DNA= negative Histone= positive
What are chromatin fibres?
Tightly packed nucleosomes
What are centromeric probes useful for?
Determining chromosome number
What are telomeric probes useful for?
Determining subtelomeric arrangements
What are whole chromosome probes and what are they useful for?
Cocktail of different probes covering different parts of a particular chromosome
Determining translocations and rearrangements
What is oogenesis?
Meiosis of the gremline cells to form ova
What is spermatogenesis?
Meiosis of gremlin cells to form sperm
What are the different types of chromosomal abnormalities and what are they?
Numerical- karyotype has wrong number of chromosomes
Structural- chromosomes rearranged
Mutational- change to DNA sequence
What is a trisomy?
Muttion causing there to be 3 copes of a particular chromosome
What does trisomy 13 cause?
Patau
What does trisomy 18 cause?
Edwards
What does trisomy 21 cause?
Downs
What does the XXY mutation cause?
Klinefelter
What does the X mutation cause?
Turner
How many gametes would be affected by a problem with disjunction in meiosis 1?
All
How many gametes would be affected by a problem with disjunction in meiosis 2?
2
Why are mutations more likely in older mothers?
Disjunction becomes less accurate the longer eggs sit having completed meiosis 1 and not 2
What are the types of translocation mutation?
Deletion Insertion Inversion Balanced Unbalanced
What is a reciprocal translocation?
Involving breaks in two chromosomes with formation of two new derivative chromosomes
What is a Robertsonian translocation?
Twi afrocentric chromosomes are fused but no genetic material is lost
What is an inversion translocation?
2 breaks in chromosome repaired incorrectly so all information is present but in wrong order
Not normally harmful unless it involves centromere
What is polymorphism?
Differences in genetic code between individuals that doesn’t cause abnormality
What are the types of coding mutations?
Silent
Missense
Nonsense
Frameshift- insertion, deletion
What is used to detect genetic mutations?
Polymerase chain reaction
Gel electrophoresis
Restriction fragment length polymorphism analysis
Amplification refractory mutation system
What is the amplification refractory mutation system used to detect?
Single base changes or small deletions
What is a disadvantage of the amplification refractory immune system?
Nature of mutation must be known
