Chromosomes Flashcards
What is G1 of the cell cycle?
The first growth phase
What is G2 in the cell cycle?
The second growth phase
What occurs at the S phase of the cell cycle?
DNA Replication
What is the M phase of the cell cycle?
The mitotic phase
How long does the mitotic phase of the cell cycle last?
1-2 hours
What happens at prophase of mitosis?
Chromosomes condense
Nucelar membranes disappear
Spindle fibres form from the centriole
What happens at metaphase of mitosis?
Chromosomes aligned at the equator of the cell
Attatched by fibre to each centriole
Maximum condensation of chromosome
What happens at anaphase of mitosis?
Sister chromatids separate at centromere
Separate longitudinally
Move to opposite ends of the cell
What happens at telophase of mitosis?
New nuclear membranes form
Each cell contains 46 chromosomes (diploid)
Cytokinesis
Cytoplasm separates
Two new daughter cells are formed
What is the centromere?
The constricted region joining sister chromatids
Where is the site of the kinetochore?
The centromere
What is the kinetochore?
Protein complex that binds to microtubules
What are required for chromosome separation during cell division?
Microtubules
What are heterochromatin?
Condensed structure
These are the silenced genes
What are euchromatin?
They are open structures
They are the active genes
How many base pairs are there?
3 million
How many genes are there roughly in DNA?
20000-30000
What percentage of DNA is protein coding?
2%
What proteins is SNA packaged with?
Histone
What charge do histone proteins carry?
Positive
DNA packaged around histone proteins are units called what?
Nucleosomes
What appearance does DNA wrapped around histones give?
Beads on a string
Nucleosomes are further wrapped how many times?
6 nucleosomes per turn
What do 6 nucleosomes wrapped form?
Solenoid structure
What effect does the histone proteins have on the charge of DNA?
The negatively charged DNA is neutralised by the positively charged histone proteins
Why is DNA folded so much?
So it takes up less space and can be compacted into the small nucleus
What is karyotype?
A test to identify and evaluate the size, shape and number of chromosomes in sample of the bodies cells
In what cells does meiosis occur?
Germ Cells
What is the purpose of meiosis?
To create a lot of genetic variation
In which diploid cells does meiosis occur?
Ovaries and testes
What is oogenesis?
The process of egg formation
What is spermatogenesis?
The process of sperm formation
What goes through more cells divisions sperm or eggs?
Sperm
When does gametogenesis commence in males?
Puberty
When does gametogenesis commence in females?
Early embryonic life
How many sperm are there per ejaculation?
100-200 million
Briefly describe the process of fertilisation
Two haploid cells form 1 diploid cell (zygote)
What does the zygote develop into?
Embryo
What is the name of the cell formed at fertilisation called?
Zygote
Where are mitochondria inherited from?
The maternal side
What is X inactivation in female mammals?
In the early embryo there can be a random inactivation of one of the X chromosomes
What are the 3 types of general chromosome abnormalities?
Numerical
Structural
Mutational
What is the incidence of chromosome abnormalities in miscarriages?
50%
What is the incidence of chromosome abnormalities in still born infants?
5%
What does trisomy mean?
Three copies of the chromosome
What is the disease caused by trisomy 21?
Down syndrome
What is the average life expectancy of someone with down syndrome?
50-60
Is trisomy 21 usually from the paternal or maternal origin?
Maternal
What disease does trisomy 13 cause?
Patau syndrome
Is trisomy 13 usually from the maternal or paternal origin?
Maternal
What does trisomy 18 cause?
Edwards syndrome
What is the prognosis of Edwards syndrome?
Most patients die within the first year and many die within the first month
Is trisomy 18 usually from the maternal or paternal origin?
Maternal
What is a balanced translocation?
This is when there is an even exchange of material between chromosomes with no genetic information extra or missing
What is an unbalanced translocation?
Where the exchange of chromosome material is unequal and results in extra or missing genes
How many chromosomes are there in robertsonian translocation/
45
What type of mutation is robertsonian?
Translocation
What happens in robertsonian translocation mutation?
Two chromosomes are fused together but no genetic information is lost
What is a deletion mutation?
A mutation where part of the genetic material is deleted and therefore missing
What is an inversion mutation?
When a piece of DNA is flipped end on end
What are the 2 types of inversion mutations?
Paracentric
Pericentric
What is a paracentric inversion mutation?
There is a break and the DNA is reinserted
What is a pericentric inversion mutation?
There is a break and the DNA is reinserted at the centromere position
What is polymorphism?
The natural variation that occurs in all people
Does polymorphism cause any disease?
No - it does not cause any disease whatsover
What is a silent mutation?
when the bases change but it codes for the same amino acid - therefore the mutaiton goes unoticed
What is a missense mutation?
When there is a change in one base and one amino acid. The protein makes come sense but not the original sense
What is a nonsense mutation?
There is a change in base, there is a change in one amino acid - however it becomes a stop codon - the protein synthesis makes no sense
What is a frameshift mutation caused by?
Deletion and insertion
What is the effect of frameshift?
All bases are subsequently changed
Is PCR and in vitro or in vivo technique?
In vitro
What are the three step of PCR?
Denature
Anneal
Extend
Roughly how many times is PCR repeated?
20-30 times
What is the purpose of PCR?
To amplify DNA
What does gel electrophoresis separate DNA fragments according to?
Size
What charge does DNA have?
Negative charge
