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AS Biology > Mitosis and Meiosis > Flashcards

Mitosis and Meiosis Flashcards

1
Q

Where are chromosomes found?

A

Animal and plant nuclei

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2
Q

What occurs just before cell division?

A

DNA is replicated and more histone proteins are synthesised, leading to temporarily twice the normal amount of chromatin in the cell.

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3
Q

What does chromatin do following replication?

A

Coils up even tighter, becoming shorter and fatter and forming chromosomes.

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4
Q

How is each chromosome shaped and why?

A

Roughly X shaped because it contains 2 replicated copies of the DNA. The 2 arms of the X are therefore gentically identical and are known as chromatids. They are joined at a centromere.

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5
Q

When are chromosomes visible?

A

Only when dividing so we only can see them in their replicated, double-stranded form

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6
Q

What are karyotypes?

A

The display of chromosomes stained, with fluorescent dye.

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7
Q

What are homologous pairs?

A

The pairs that chromosomes come in with same size, shape and banding pattern.

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8
Q

What are autosomes?

A

Non sex chromosomes- humans have 22 pairs

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9
Q

What is the different pair of chromosomes in males and females?

A

Sex chromosomes- homologous in females (XX)

Non-homologous in males (XY)

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10
Q

Why do we have 2 copies of each chromosome?

A

We inherit 1 from each parent, so homologous pairs consist of a maternal and paternal version of the same chromosome.

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11
Q

What are most cells in the body?

A

Somatic cells, contain homologous chromosome pairs

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12
Q

What are diploid cells?

A

Cells that contain 2 sets of chromosomes (2n)

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13
Q

What are haploid cells?

A

Cells that have only 1 chromosome set (n)

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14
Q

What type of cells are somatic and what do they contain in humans?

A

Diploid- 23 pairs

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15
Q

What type of cells are gametes and what do they contain in humans?

A

Haploid- sex cells produced in testes and ovaries, contain 23 chromosomes

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16
Q

What is cell division?

A

The process whereby a cell splits to form daughter cells.

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17
Q

What are the 3 main stages of the cell cycle?

A
  • Interphase-period of synthesis and growth.
  • Mitosis/meiosis- period of nuclear division.
  • cell division-process of division of the cytoplasm into 2 daughter cells (known as cytokinesis).
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18
Q

What is the largest stage of the cell cycle and how much does it make up?

A

Interphase- about 90%

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19
Q

What are the stages of mitosis (PMAT)?

A

Prophase
Metaphase
Anaphase
Telophase (inc. cytokinesis)

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20
Q

What occurs during the interphase?

A

•DNA replicated

  • new organelles sythesised
  • active process so ATP production
  • protein sythesis producing more histone proteins
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21
Q

How does interphase appear in a diagram?

A

Scribbles in central nucleus. Scribbles = chromatin.

22
Q

What occurs during the prophase?

A
  • nuclear envelope + nucleolus disappears.
  • duplicated chromatin condenses to form chromosomes which join at a centromeres so can now be called a pair of sister chromatids.
  • in animal cells, centrioles move to opposite poles of the cell.
  • spindle fibres start to form
23
Q

How is the prophase shown in a diagram?

A

Chromosomes joined at centromere visible and scattered.
Partially formed spindle fibres visible.
Disintegrating nuclear membrane seem

24
Q

What are chromosomes made of?

A

A single molecule of DNA tightly wrapped around proteins to form chromatin.

25
Q

What happens in the metaphase?

A

Chromosomes randomly line up at cell’s ewuator.

  • they attach to the spindle fibres by their centrosomes.
  • relatively short so difficult to observe on a slide section
26
Q

How is metaphase shown in a diagram?

A

Chromatids along equator, spindle fibres run from centromeres to membrane.

27
Q

What happens in the anaphase?

A

-centromeres divide and spindle fibres contract
-this separates the sister chromatids to the opposite poles of the cell (centromere first)
Called chromosomes once separated

28
Q

How is the anaphase shown on a diagram?

A

Separated chromatid pairs are being pulled to opposite poles by contracted spindle fibres, centromere leading.

29
Q

What occurs during the telophase?

A
  • the chromosomes reach the poles + uncoil to form chromatin.
  • the spindle fibres break down
  • a nuclear envelope + nucleolus forms around each set of chromosomes.
30
Q

How is telophase shown in a diagram?

A

Looks like two separate nuclei in a cell with breaking down spindle fibres inbetween

31
Q

What happens in cytokinesis in animals?

A

The cell divides due to constriction of the centre of the parent cell from the outside inwards, producing a cleavage furrow.

32
Q

What happens in cytokinesis in plants?

A

The cell divides by growth of a growth plate across the centre of the parent cell from the centre outwards.

33
Q

How does cytokinesis appear in a diagram?

A

Looks like two cells separating.

34
Q

What are the 3 significant uses of mitosis?

A

Growth
Repair of damaged tissues
Asexual reproduction

35
Q

How is mitosis good for growth?

A

As multicellular organisms grow, the number of cells making up their tissues increases. New cells must be genetically identical to existing ones.

36
Q

Mitosis for repair of damaged tissue with example:-

A

Damaged cells must be replaced by exact copies of the originals. E.g skin cells are constantly shed and must be replaced.

37
Q

Mitosis for asexual reproduction 2 examples:-

A

Producing plants like tulips.

Bacteria, fungi and yeasts- it allows a rapid increase in numbers, advantageous when colonising new habitats.

38
Q

How can cancer occur?

A

Cancer occurs as a result of mutations during DNA replication (interphase) can lead to the formation of groups of cells called tumours.

39
Q

What are the genes involved with cancers classed as?

A

Proto-oncogenes or tumour supressor genes.

40
Q

How do proto-oncogenes cause cancers?

A

Encode proteins that function to stimulate cell division, inhibit cell differentiation and halt cell death.
-Mutated version is called an oncogene- results in increased protein prod, increased cell division and inhibition of cell death.
This results in the formation of tumours.

41
Q

How do tumour supressor genes work?

A
  • can restrain inappropriate cell growth and division as well as stimulating cell death to help keep our cells in proper balance- this acts as a ‘brake’ to cells from becoming cancerous.
  • when TS cells mutate function is lost and so leads to uncontrolled cell division.
42
Q

What does meiosis do?

A

Occurs in diploid cells during gamete formation.
Involves 2 consecutive cell divisions and produces four haploid daughter cells from a single parent cell. Consecutive cell divisions referred to as meiosis I and meiosis II.

43
Q

Where do the main differences between mitosis and meiosos occur?

A

Between mitosis and meiosis I as mitosis and meiosis II are almost identical

44
Q

What is it important to remember about Prophase 1?

A

Chromatid of one chromosome crosses over with another, swapping genetic info?

45
Q

What is independent assortment?

A

The random way chromosomes arrange themselves at the equator.

46
Q

How is Prophase I different to mitosis’ prophase?

A

Homologous chromosomes pair up to form bivalents.

Chiasmata form and crossing over may occur, giving rise to genetic variation.

47
Q

How is metaphase I diff to mitosis metaphase?

A

Homologous chromosome pairs (bivalents) randomly line up SIDE BY SIDE at cell equator.

48
Q

How is anaphase I different to mitosis’ anaphase?

A
  • centromeres don’t divide
  • so whole chromosomes are pulled to opposite poles of cell, not chromatids.
  • chromosomes may not be genetically identical due to crossing over.
49
Q

How is telophase I diff?

A
  • half no. of chromosomes present in daughter cells
  • 1 pair of homologous chromosomes present in daughter cells.
  • no uncoiling to form chromatin
50
Q

How does interphase II work?

A

NO DNA REPLICATION

-in some species may be a slight delay pre meiosis II, in many is simply absent.

51
Q

What uniquely occurs in prophase II?

A

Spindle forms at right angles to meiosis I’s spindle.

52
Q

What are the 4 points genetic variation can occur?

A
  • random gamete fusion during fertilisation.
  • Prophase I crossing over= homologous pair of chromosomes in a bivalent swap genes at the chiasmata
  • independent assortment (metaphase I)
  • natural selection (genetic variation within a population = longterm survival)

AS Biology (14 decks)

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