IMMS Flashcards
What is the final step of mitosis?
Cytokinesis
What happens in Interphase G1?
no visible activity but the following occurs
• Rapid growth
• Normal metabolic function
• New organelles produced
• Protein synthesis of proteins involved in spindle formation
S (synthesis):
• DNA doubles through DNA replication
• Histone proteins double through protein synthesis ( 2 x as much DNA at end of S)
• Centrosome replication
What happens in Interphase G2?
- Chromosomes condense (coil up and become visible)
- Energy stores accumulate
- Mitochondria and centrioles double
What happens in Prophase?
- Chromatin condenses into chromosomes
* Centrosomes nucleate microtubules and move to opposite poles of nucleus
What happens in Prometaphase?
- 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?
• 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
- 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
What is the connection between mitosis and malignancy?
Something is defined as malignant if there are too many mitotic figure i.e. lots of dark
nuclei of different sizes
- Number of mitotic figures determine how bad cancer is, the more there are, the worse
it is
What are produced by meiosis?
4 haploid (HALF number of chromosomes i.e. 23) cells produced, which are genetically distinct from each other and the parent cell
What happens in Meiosis 1?
• Chromosome number is halved
• In Prophase 1, crossing over occurs between non-sister chromatids [genes sort
independently thus if 1 gene switches over, doesn’t mean another one will], resulting
in genetic diversity
• In Metaphase 1, random assortment occurs on the metaphase plate - also resulting in
genetic diversity
What happens in Meiosis 2?
Sister chromatids separate
• Haploid cells produced
How many days does male gametogenesis take?
60-65 days
How many sperm per ejaculate?
100-200 million
How many times must a primordial germ cell mitose to become an oogonia?
30
When do Oogonia enter prophase 1?
Oogonia enter prophase 1 of meiosis 1 by 8th month of intrauterine life (in-utero)
Does the cytoplasm divide equally in female gametogenesis?
No, cytoplasm divides unequally - 1 egg & 3 polar bodies (that apoptose - go on to die)
When is Meiosis 2 completed in female gametogenesis?
At fertilisation
What is Mendel’s Second Law?
Thelawof independent assortment states that a pair of trait segregates independently ofanotherpair during gamete formation. As the individual heredity factors assort independently, different traits get equal opportunity to occur together.
What is non-disjunction?
Failure of chromosome pairs to separate in Meiosis 1 or sister chromatids to separate properly in meiosis 2.
How can non-disjunction cause Down’s Syndrome? What are the percentages involved?
Can result in downs syndrome (non-disjunction at chromosome 21 resulting in trisomy 21) ~75% maternal meiosis I ~25% maternal meiosis II ~3-5% paternal non disjunction
How does non-disjunction cause Turner’s Syndrome?
monosomy (loss of a chromosome) - Turners syndrome, only 1 X chromosome.
What is gonadal mosaicism?
Occurs when precursor germline cells to ova or spermatozoa are a mixture of two or more genetically different cell lines (due to errors in mitosis)
• One cell line is normal, the other is mutated
• Incidence increases with advancing paternal age
• Parent is healthy ( since genetic change is only in the germline so all the other cells
are unaffected - have usual genetic components), but the foetus may have genetic
diseases
• More common in males
• Can be observed with any inheritance pattern, but most commonly autosomal
dominant and X - linked
• Observed in a number of conditions, including osteogenesis imperfect and duchenne muscular dystrophy