Lecture 5: Mitosis And Meiosis Flashcards
Why are mitosis and meiosis important in genetics?
They are the methods by which a eukaryotic cell transmits its genetic information to daughter cells (mitosis) or the next generation (meiosis).
The differences between these mechanisms explain the different genetic outcomes.
What is the cell cycle made up of?
Interphase (G1, S, G2) and mitosis.
What is G0?
Quiescence, the phase when cells enter the period of dormancy/inactivity. Most of the cells in our body are in this phase (they wait until they need to be activated).
What are cell cycle checkpoints?
Control mechanisms in the eukaryotic cell which ensure its proper progression.
Decide whether or not a cell can proceed to the next stage of the cycle based on factors.
What will happen if there is a defective checkpoint?
Disease will form.
How does DNA content change?
It doubles during S phase when the DNA replicates, therefore cells in G2 have double the DNA content of a G1 cell.
In mitosis, half of the DNA goes into each daughter cell, taking the DNA content back down to G1 levels.
How does a cell prepare for mitosis?
• Centrioles duplicate during S phase.
• Nuclear envelope breaks down.
• DNA condenses into mitotic chromosomes.
• Centrioles migrate to opposite poles and form spindle fibres.
• Condensed chromosomes align on spindle fibres.
How does approximately 2m of DNA fit into a 5-10 micron nucleus?
It gets compacted and packaged into chromosomes.
What are somatic cells?
All but reproductive cells in diploid organisms.
What are some several layers of compaction?
- Nucleosomes – 147 bp DNA (which is negatively charged) wrapped around positively charged octamer histone core - ‘beads on a string’ with a diameter of 11 nm.
- Solenoid – coiling of nucleosomes giving 6-fold compaction that has a 30nm diameter.
- Chromosome – solenoids coil into 300 nm fibres, which condense into a 700nm (diameter of a chromatid) chromosome.
What is a chromatosome?
Consists of a nucleosome plus the H1 histone.
How is the chromatin fiber formed?
Solenoid fibres form loops (averaging 300nm in length).
What is a diploid cell?
Containing two complete sets of chromosomes, one from each parent.
Made up of two haploid (single set of unpaired chromosomes n=23) cells.
What is a homologous chromosome?
Similar paired chromosomes that may differ in alleles. One maternal copy and one paternal.
What is the difference between homologous chromosomes and sister chromatids?
Sister chromatids are the duplicated forms of each homologous chromosome.
While homologous chromosomes have same genes, their alleles differ. Sister chromatids have the same genes and alleles.
What happens during anaphase to sister chromatids?
They split, one into each daughter cell.
M-P, M-P.
Why does DNA condense when it is about to split?
A messy ‘soup’ of loose DNA would be very difficult to split accurately between daughter cells.
What is a karyotype?
An individual’s complete set of chromosomes.