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Year 1 Semester 1 Medical Cell Biology and Genetics > S2) Mitosis and Meiosis > Flashcards

S2) Mitosis and Meiosis Flashcards

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1
Q

Identify all the stages in the cell cycle

A
  • G1
  • S Phase
  • G2 Phase
  • M Phase
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2
Q

Describe what happens the G1 phase and when it begins

A
  • Begins immediately after mitosis
  • Synthesis of RNA, proteins, and organelles
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3
Q

Describe what occurs in the S Phase

A

DNA replication occurs, i.e. chromosomes form sister chromatids

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4
Q

Describe what occurs in the G2 Phase

A
  • Mitochondria divide
  • Synthesis of precursors of spindle fibres
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5
Q

Identify all the stages of M Phase (mitosis)

A
  • Prophase
  • Prometaphase
  • Metaphase
  • Anaphase
  • Telophase
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6
Q

What occurs in prophase?

A
  • Chromatin condenses due to supercoiling and chromosomes become visible
  • Nucleoli disappear
  • Nuclear envelope breaks down
  • Centrioles divide and migrate to opposite poles
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7
Q

What occurs in prometaphase?

A
  • Microtubules produce spindle fibres form
  • Spindle fibres attach to centromere of chromosomes
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8
Q

What occurs in metaphase?

A

Chromosomes, with spindle fibres attached, line up on the equator of the dividing cell

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9
Q

What occurs in anaphase?

A
  • Centromeres divide, converting each sister chromatid into a chromosome
  • Chromosomes migrate toward opposite ends of the cell until there is a complete set of chromosomes at each end of the cell
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10
Q

What occurs in telophase?

A
  • Chromosomes reach the opposite poles of the cell
  • Chromatin decondenses & spindle fibres break down
  • Nuclear membrane reforms
  • Nucleoli reappear
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11
Q

What occurs in cytokinesis?

A
  • Cleavage furrow forms at equator of cell and deepens
  • Cytoplasm divides
  • New nuclear envelope forms
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12
Q

Describe the structure of chromosomes

A
  • Each chromatid consist of one identical DNA molecule
  • Each chromatid has a p (short) and q (long) arm
  • Telomeres at the end of each chromatid
  • Centromeres link sister chromatids
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13
Q

Identify the different types of chromosome structures

A
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14
Q

What occurs in meiosis?

A
  • Members of a chromosome pair separate from each other
  • Each daughter cell receives a haploid (n) set of 23 chromosomes
  • These haploid cells form gametes (sperm and egg)
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15
Q

Explain the reduction that occurs in meiosis

A
  • Before cells enter meiosis, the chromosomes replicate during interphase
  • Meiosis I reduces the chromosome number accomplished by two rounds of division (meiosis I and meiosis II)
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16
Q

How does fertilisation affect the overall chromosome number?

A
  • Fusion of two haploid gametes in fertilisation restores the chromosome number to the diploid number of 46
  • Fertilised egg has a full set of genetic information
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17
Q

Explain what is meant by the following terms:

  • Homologous chromosomes
  • Sister chromatids
  • Non-sister chromatids
A
  • Homologous chromosomes have the identical DNA but may have different alleles
  • Sister chromatids have identical DNA and the same alleles
  • Non-sister chromatids have identical DNA, but may have different alleles
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18
Q

How does recombination occur in meiosis I?

A

Meiosis produces new combinations of parental genes in two ways:

  • Random assortment which puts random combinations of maternal and paternal chromosomes into gametes
  • Crossing over which is the exchange of chromosome segments between non-sister chromatids of homologous chromosomes
19
Q

What occurs in prophase I of meiosis?

A
  • Chromatin condenses & chromosomes are visible
  • Homologous chromosomes pair & crossing over occurs
  • Newly forming spindle microtubules become attached to each chromosome
20
Q

What occurs in metaphase I of meiosis?

A
  • Paired chromosomes align at equator of cell
  • Random assortment of chromosomes occurs
21
Q

What occurs in anaphase I of meiosis?

A
  • Paired homologous chromosomes separate
  • Sister chromatids move to opposite poles
22
Q

What occurs in telophase I of meiosis?

A
  • Chromosomes uncoil
  • Spindle fibres break down
  • Nucleoli & nuclear envelop reform
23
Q

What occurs in cytokinesis of meiosis I?

A
  • Cytoplasm divides
  • 2 haploid daughter cells are formed
  • All chromosomes are still in the duplicated state
24
Q

Outline Meiosis II

A
  • Prophase II: Chromosomes re-coil and shorten
  • Metaphase II: Unpaired chromosomes become aligned at equator of cell
  • Anaphase II: Centromeres separate. Daughter chromosomes, which were sister chromatids, pull apart
  • Telophase II: Chromosomes uncoil and nuclear envelope re-forms
  • Cytokinesis: Cytoplasm divides forming 4 haploid daughter cells
25
Q

What is spermatogenesis?

A

Spermatogenesis is the production of sperm which occurs in the testes of males

26
Q

Outline the process of spermatogenesis

A
27
Q

What is oogenesis?

A

Oogenesis is the production of gametes (ova) which occurs in the ovaries of females

28
Q

Outline the process of oogenesis

A
29
Q

Describe the phenomena of missegregation in meiosis

A
  • 30% of human meiosis is faulty
  • Consequences: miscarriages and infertility
30
Q

How can chromosomes be analysed?

A

Metaphase spread:

  • Stained metaphase chromosomes
  • Actively dividing cells are needed
31
Q

State the standard format used to describe the karyotype

A

Karyotype = Chromosome number, sex complement, structural changes (no spaces)

  • E.g. 46,XX - normal female*
  • E.g. 47,XY,+21 - male with trisomy 21*
32
Q

What is mitotic non-disjunction?

A

Mitotic nondisjunction is when daughter cells have abnormal chromosome numbers (aneuploidy) due to the failure of sister chromatids separating in anaphase of mitosis

33
Q

Aneuploidy can result fron non-disjunction.

Define this term

A

Aneuploidy is the presence of an abnormal number of chromosomes in a cell

34
Q

What is mosaicism?

A

- Mosaicism is the presence of 2/more cell lines in an individual

  • It can occur throughout the body or be tissue limited
  • Non-disjunction can cause mosaicism
35
Q

What influences the degree of mosaicism?

A
  • When the first post-zygotic division occurs
  • When later mitotic divisions occur
36
Q

What is the role of the mitotic spindle in mitosis?

A

The mitotic spindle ensures the accuracy of chromosome segregation

37
Q

The mitotic spindle is a proven target for successful cancer treatment.

Explain how

A
  • Cancer cells are aneuploid (not diploid) and exhibit chromosome instability
  • Treatments interfere with microtubules, preventing cell division in rapidly-dividing cancer cells
38
Q

Cancer cells often display numerical chromosome instability (CIN).

What causes this?

A
  • Mitotic errors promote CIN and tumour heterogeneity
  • Amplified centrosomes, often seen in cancer, produce multipolar spindles which also promote CIN
39
Q

What regulates spindle polarity?

A

Spindle polarity is regulated by centrosome number

40
Q

What is the role of TSG?

A

Tumour suppresor genes (TSG) stop cancer growth

41
Q

What is the role of oncogenes?

A

Oncogenes promote cancer growth

42
Q

What results from TSG and oncogene mutations?

A

Centrosome amplification results from TSG and oncogene mutation

43
Q

What is centrosome clustering and what does it do?

A
  • Cancer cells have mechanisms to cluster amplified centrosomes
  • Clustering extra centrosomes allows cancer cells to survive
44
Q

Identify a therapeutic strategy targeting centrosome clustering

A

Inhibition of centrosome clustering to lead to cancer cell death

Year 1 Semester 1 Medical Cell Biology and Genetics (23 decks)

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