22. Cell reproduction. Haploid-Diploid cycle. Aberrations in the normal run of mitosis and meiosis. Flashcards Preview

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Flashcards in 22. Cell reproduction. Haploid-Diploid cycle. Aberrations in the normal run of mitosis and meiosis. Deck (12):
1

How do prokaryotes reproduce

Prokaryotes reproduce asexually through binary fission (a single cell is divided into 2 cells of the same size). Eukaryotes divide by mitosis/ meiosis

2

What are the definitions of Mitosis and Meiosis?

Mitosis - cell division where a parent cell forms 2 identical daughter cells

Meiosis - cell division where daughter cell contains half the info from parent cell

3

Give a brief explanation of meiosis

Meiosis

- only found in sex cells - gametes

- somatic cells CANNOT divide by meiosis
- gametes are haploid (n)
- fertilisation = when oocyte and spermatozoan fuse - becomes diploid (2n)
- mitosis of cells to make organs…
- mitosis - diploid progeny cells
- each gamete has either a maternal or paternal version of each chromosome - the choice is random for each pair

- Crossing over: happens only in meiosis for gametes, it’s the exchange of genetic material from maternal + paternal versions of each chromosome. Generates genetic diversity

4

Explain Mitosis interphase

Mitosis:

INTERPHASE
G1:

- growth phase - cell grows

- synthesises mRNA and proteins

S:

- synthesis phase - DNA is replicated

- (DNA packaged in chromosomes are replicated)

G2:

- Rapid cell growth + protein synthesis

- cell gets ready for mitosis
- safety gap - check if DNA has been duplicated properly

5

Explain the (M phase) Of mitosis:

Stages: Prophase, prometaphase, metaphase

M PHASE

Prophase:
- chromosomes condense

- mitotic spindle assembles

Prometaphase:

- nuclear envelope fragments

- chromosomes attach to microtubules

Metaphase:

- chromosomes at the equator (middle)

- chromatids attach to the mitotic spindle

6

Explain the (M phase) Of mitosis:

Stages: Anaphase and telophase

Explain the final stage cytokinesis

Anaphase:

- kinetochore microtubules shorten

- chromosomes separate

Telophase:

- chromosomes at the pole

- nuclear envelope reassembles

Cytokinesis:

- cleavage

- nuclear envelope completed

7

Explain Meiosis
stage: interphase

Meiosis:
INTERPHASE - before meiosis begins, genetic material is duplicated MEIOSIS I

8

Explain Meiosis
stage: Prophase I and its substages

Prophase I:
- duplicated chromatin condenses

- each chromosome consists of 2, closely associated sister chromatids
- (crossing over at the end stage)

Leptotene:

- consists of the condensing of replicated chromosomes

- each sister chromatid is attached to nuclear envelope

Zygotene:

- synapsis between homologous chromosomes begins

- after homologous pairs synapse, they are called tetrads, bivalents

Pachytene:

- synapses snap, allowing crossing-over of genetic info

- 2 sister chromatids separate from each other
- homologous chromosomes are attached

Diplotene:

- 2 homologous chromosomes begin to migrate apart - repel one another

- 2 chromosomes move apart
- chiasma move to end of chromatids

Diakinesis:

- Termination of the condensing of chromosomes

- chromosomes are at there most condensed
- nucleolus disappear

9

Explain Meiosis
stages: Metaphase I, Anaphase I and Telophase I

Metaphase I:

- homologous chromosomes align at the equatorial plate

Anaphase I:

- homologous pairs separate with sister chromatids remaining together

Telophase I:

- 2 daughter cells are formed with each daughter containing only 1 chromosome of the homologous pair

10

Explain MEIOSIS II:

Stages: Prophase II, Metaphase II, Anaphase II and Telophase II.

MEIOSIS II:
Prophase II:
- DNA does NOT replicate

Metaphase II:

- chromosomes align the equatorial plate

Anaphase II:

- centromeres divide + sister chromatids migrate separately to each pole

Telophase II:

- cell division is complete

- 2 haploid daughter cells are obtained

11

Aberrations during Meiosis:
1) What is Aneuploidy

Aneuploidy - addition or loss of one or two chromosomes
- Non-disjunction - chromatids don’t separate properly

- (division failure of sister chromatids)
- multipolar mitosis - 3 or more poles

12

Aberrations during Meiosis:
2) What is Polyploidy

Polyploidy - addition of complete haploid sets of chromosomes

- endomitosis, chromosomal replication not followed by cytokinesis

- endoreduplication, cells grow + enlarge, but don’t go through process of dividing - mitosis

- C mitosis, colchicine block mitotic anaphase (colchicine blocks mitotic spindles contracting

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