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Wjec Biology As Unit 1 > 1.6 > Flashcards

1.6 Flashcards

1
Q

What do chromosomes consist of

A

DNA and histone

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2
Q

When are chromosomes visible

A

After they condense at the onset of cell division

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3
Q

Following DNA replication what does a chromosome exist as

A

Two identical sister chromatids joined by the centromere

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4
Q

What do chromosomes contain

A

Genes that code for specific polypeptides

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5
Q

How manu chromosomes do humans have

A

46

23 pairs

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6
Q

What are homologous chromosomes?

A

Chromosomes that are the same size and shape and carry the same genes but these may be different versions called alleles.
One chromosome of
each pair comes from each
parent

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7
Q

Two complete sets of chromosomes

A

Diploid 2n

Humans - 46

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8
Q

What is haploid and where are haploid numbers found

A

n

Human gametes

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9
Q

What are the stages of the cell cycle

A

Interphase
Mitosis
Cytokines

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10
Q

Define interphase

A

a period of synthesis and growth during the cell cycle

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11
Q

Describe interphase

A
  • longest cell cycle phase
  • very metabolically active
  • DNA quantity doubles (chromosome number remains as it becomes 2 sister chromatids)
  • protein synthesis
  • organelle replication
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12
Q

What is mitosis

A

Chromosomes are arranged and separated prior to cell division
Results in two genetically identical cells that contain the same number or chromosomes as the parent cell

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13
Q

What happens during prophase of mitosis

A

• Chromosomes condense to become shorter and thicker
• Chromosomes become visible as two sister chromatids attached by a centromere
• Centrioles move to opposite
poles (not higher plants)
• Nuclear envelope disintegrates
• Nucleolus disappears

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14
Q

Which stage

A

Prophase of mitosis

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15
Q

What happens during metaphase of mitosis

A
  • Spindle forms

* Chromosomes align at the equator of the cell attached to spindle microtubules via centromere

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16
Q

Which stage

A

Metaphase of mitosis

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17
Q

What happens during anaphase of mitosis

A
  • Spindle fires shorten

* Centromeres divide, and chromatids are pulled towards opposite poles

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18
Q

Which stage

A

Anaphase of mitosis

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19
Q

What happens during telophase of mitosis

A 
• Chromatids reach poles and
become indistinct by uncoiling
• Nuclear envelope reforms
• Nucleolus reforms
• Spindle disintegrates
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20
Q

Which stage

A

Telophase of mitosis

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21
Q

What is cytokinesis

A

the division of the cytoplasm to form

two daughter cells

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22
Q

Animal cytokinesis

A

membrane infolds via cleavage furrow until the two cells become separated

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23
Q

Plant cell cytokinesis

A

Cell plate develops from the centre outwards until the cell is divided into two

24
Q

Why is animal and plant cytokinesis different

A

Plants have cellulose cell walls which prevents them from forming a cleavage furrow

26
Q

What is the significance of mitosis

A

Growth, repair and asexual reproduction
Animal - blood and skin cells are constantly replaced
Plant - root and shoot tip meristems constantly undergo mitosis

27
Q

What is a proto-oncogene?

A

Gene that has the potential to cause cancer

28
Q

Describe the cell division which leads to the formation of tumours and cancers

A

Uncontrollable

29
Q

How does vincristine help treat cancer

A
  • prevents formation of spindle so arresting mitosis at metaphase
  • slows the rate of cell division
30
Q

Define meiosis

A

Two consecutive cell divisions to produce four genetically different, haploid cells

31
Q

Where does meiosis occur

32
Q

When does interphase occur during meiosis

A

Before prophase 1

34
Q

What increases genetic variation during meiosis

A

Bivalents crossing over

Independent assortment

35
Q

What happens during prophase 1 meiosis

A
  • Chromosomes condense to become shorter and thicker
  • Centrioles move to opposite poles (not higher plants)
  • Chromosomes come together in homologous pairs (bivalent)
  • Crossing over occurs - part of one chromatid is exchanged with another
  • Nucleolus and nuclear membrane disappear
36
Q

DNA content and chromosome number per cell during prophase 1

37
Q

What happens during metaphase 1

A

• Spindle forms
• Homologous chromosome pairs (bivalents) align at the equator of the cell attached to spindle microtubules via centromere
• This alignment is random and called
independent assortment

38
Q

DNA content and chromosome number per cell metaphase 1

39
Q

What happens during anaphase 1

A
  • Spindle fires shorten

* Bivalents separate and chromosomes are pulled towards opposite poles

40
Q

DNA content and chromosome number per cell in anaphase 1

41
Q

What happens during telophase 1

A

Chromosomes reach poles

42
Q

DNA content and chromosome number per cell in telophase 1

43
Q

Cytokinesis of meiosis 1

A

Division of cytoplasm

2 haploid cells

44
Q

What happens during prophase 2

A

Centrioles separate, and arrange

themselves at 90° to the previous spindle

45
Q

DNA content and chromosome number per cell in prophase 2

46
Q

What happens during metaphase 2

A

Chromosomes align at the equator of the cell attached to spindle microtubules via centromere

47
Q

DNA content and chromosome number per cell in metaphase 2

48
Q

What happens during anaphase 2

A
  • Spindle fires shorten

* Centromeres divide, and chromatids are pulled towards opposite poles

49
Q

DNA content and chromosome number per cell in anaphase 2

50
Q

What happens during telophase 2

A 
• Chromatids reach poles and become
indistinct
• Nuclear envelope reforms
• Nucleolus reforms
• Spindle disintegrates
51
Q

DNA content and chromosome number per cell in telophase 2

52
Q

Cytokinesis meiosis 2

A

Four haploid cells produced

53
Q

DNA content and chromosome number per cell in cytokinesis of meiosis 2

54
Q

DNA content and chromosome number per cell in cytokinesis of meiosis 1

55
Q

What is the significance of meiosis

A
  • genetic variation- crossing over and independent assortment
  • keeps constant chromosome number - gametes recombine during fertilisation which restores diploid number

Wjec Biology As Unit 1 (7 decks)

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