Mitosis and Meiosis Flashcards
State main features of DNA and base pairing:
- Double helix
- Complimentary base pairs A - T (2 bonds), C - G (3 bonds)
- Coils into nucleosomes (around histone proteins) > supercoils > chromosomes
How many pairs of chromosomes and what are they?
46 chromosomes, 22 autosome pairs, 1 pair sex chromosome XY - male & XX - female
Name the the three parts of a chromosome:
Long arm, q
Short arm, p
Separated by a centromere
What is a telomere and what does it do?
End section of chromosome.
Stop chromosome unravelling, shortens with each division, tolermerase rebuilds telomere.
What does mitosis produce and what is it used for ?
- Produce 2 genetically identical daughter cells,
- Growth, replace dead cells
Name the phases of mitosis:
Interphase - G1,S,G2
Prophase
Pro metaphase
Metaphase
Anaphase
Telophase
Cytokinesis
What happens in Interphase: G1
G1: no visible activity but the following occurs
- Rapid growth
- Normal metabolic function
- New organelles produced
- Protein synthesis of proteins involved in spindle formation
What happens in Interphase: S phase
- DNA x2 through DNA replication
- Histone proteins x2 through protein synthesis ( 2 x as much DNA at end of S)
- Centrosome replication
What happens in Interphase: G2
G2 - 4n chromosomes (normally 2n)
- Chromosomes condense (coil up and become visible)
- Energy stores accumulate
- Mitochondria and centrioles doubles
What happens in prophase:
- Chromatin condenses into chromosomes
- Centrosomes nucleate microtubules and move to opposite poles of nucleus
What happens in pro metaphase:
- Nuclear membrane breaks down
- Microtubules invade nuclear space
- Chromatids attach to microtubules
- Cell no longer has a nucleus
What happens in metaphase:
Chromosomes line up along equatorial plane (metaphase plate)
What happens in anaphase:
- Microtubules shorten
- Sister chromatids separate, and are pushed to opposite poles of the cells, centromere first, as spindle fibres contract
What happens in telophase:
- Nuclear membrane reforms around 2 nuclei
- Chromosomes unfold into chromatin
- Cytokinesis begins
What happens in cytokinesis:
- Cell organelle become evenly distributed around each nucleus
- Cell divides into two daughter cells with a nucleus in each and 46 chromosomes
Clinical relevance of mitosis:
- Detect chromosomal abnormalities eg downs syndrome
- Categorise tumours as - benign or malignant
- In histology - mitotic cells dark nucleus
- Grading malignant tumours - too many mitotic figure i.e. lots of dark nuclei of different sizes
- No. of mitotic figures determine how bad cancer is, the more there are, the worse it is
- Anti mitosis drug - taxol (mitotic spindle), ispinesib (spindle poles) and colchicine like drugs (anaphase) can help treat cancer?
First stage of gametogenesis:
The first stage is the proliferation of primordial (undifferentiated) germ cells by mitosis
When does mitosis occur in male gametogenesis?
Some mitosis occurs in embryonic stages to produce primary spermatocytes present at birth
Mitosis begins during puberty, continues throughout life
How many gametes are produced in male gg and how long does it take?
- Cytoplasm divides evenly
- After meiosis 2 - four equal size gametes
- Takes 60-65 days
How many mitoses occur in female gametogenesis?
30
When does oogonia enter meiosis?
- Oogonia enter prophase 1 of meiosis 1 by 8th month of intrauterine life (in-utero)
- Process suspended
- Meiosis 1 is completed at ovulation 10-50 yrs later (then cells remain in suspended animation) - at this point there is 1 big cell, 1 small cell each with diploid DNA. Then go on to divide again each, after fertilisation
- Meiosis 2 is only completed if fertilisation occurs
What is produced after female gg:
Cytoplasm divides unequally - 1 egg & 3 polar bodies (that apoptose after meiosis 2)
Issues with meiosis:
- Non disjunction - Chromosomes don’t separate after M1 or sister chromatids in M2
- Downs syndrome - Non-disjunction at chromosome 21 resulting in trisomy 21
- Monosomy (loss of chromosome) - Turners syndrome, only 1 X chromosome.
What is Gonadal mosaicism:
Precursor germline cells to ova or spermatozoa are a mixture of two or more genetically different cell lines (due to errors in mitosis - random mutation)
