Sesh 3: Mitosis & Meiosis Flashcards
What is G0?
A stage in the cell cycle in which the cell is inactive/resting.
Some cells enter this permanently, whilst some enter and leave this stage.
What shape is a replicated chromosome?
The classical X shape- consists of 2 identical sister chromatids.
The short arm of a chromatid is the ‘’ arm, and the long arm is the ‘’ arm.
- P (petit)
2. Q
What is mitosis?
Cell division for somatic cells, that produces 2 identical daughter cells with the same chromosome content as the parent cell.
Name the 5 phases of mitosis.
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase
What stage in the cell cycle occurs after mitosis?
Cytokinesis
What are telomeres?
Repeated sequences/ conserved regions at each end of a chromosome/ chromatid that shorten every time the cell divides.
What occurs in prophase of mitosis?
- nuclear envelope begins to disappear
- chromosomes condense and become visible
What is a centromere?
It links sister chromatids of a chromosome and consists of repetitive sequences.
What happens in prometaphase of mitosis?
- nuclear envelope has completely disappeared
- microtubule spindles connect to centromeres via the kinetophore
What occurs in metaphase of mitosis?
All 46 chromosomes line up along the metaphase plate in a random manner.
Describe the anaphase of mitosis.
The microtubular spindles contract and pull each replicated chromosome apart, meaning the sister chromatids (now called chromosomes) are pulled to opposite poles of the cell.
What 4 things occur in telophase of mitosis?
- spindles disappear
- nuclear envelope begins to reform
- chromosomes decondense
- cleavage furrow begins to form
What are chromosomes like when not undergoing cell division e.g. In interphase?
They are visible but not condensed.
2 models:
1. Each chromosome has its own territory/volume within the nucleus
2. Chromosomes in nucleus= a random bowl of spaghetti- random organisation
Homologous chromosomes have the ____ DNA sequence, and the ____ genes, but may have different _________.
- Same
- Same
- Alleles
Do sister chromatids have the same or different DNA?
The same, and same alleles, as are products of DNA replication.
What is meiosis?
Cell division of germ line cells, that produces 4 non-identical haploid daughter cells.
What is different about metaphase and anaphase in meiosis I, compared to mitosis?
Instead of all 46 chromsosomes lining up individually in a random manner as in mitosis, the pairs of homologous chromosomes line up together along the metaphase plate, so that when the spindle contracts, the homologous pairs separate rather than the sister chromatids of the replicated chromosomes.
What is recombination/crossing over and when does it occur?
Crossing over occurs in prophase I of meiosis I, and is the exchange of genetic material between non-sister chromatids of a homologous pair at chiasma/chiasmata. This produces genetic variation.
What is random assortment?
In meiosis I, pairs of homologous chromosomes line up along the metaphase plate in a random manner, meaning that when they separate in anaphase I, whether the daughter cell receives maternal or paternal chromosomes is random. This contributes to genetic variation…
What is a tetrad?
It is a bivalent grouping of a pair of homologous chromosomes- each chromosome consists of 2 sister chromatids.
Formed in prophase I, when homologous chromosomes ‘find each other’.
What are the 2 consequences of meiosis?
- Maintaining a constant chromosome number from generation to generation
- Generation of genetic diversity (crossing over and random assortment)
What is the main difference between meiosis I and meiosis II?
Meiosis I- homologous pairs of chromosomes line up and separate, to produce 2 haploid cells (23 replicated chromosomes each)
Meiosis II- chromosomes line up and chromatids separate, to produce 4 haploid cells (23 chromosomes)
How do spermatogonia become primary spermatocytes?
Via mitosis (both =2n)- replenishes the germ pool.
