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1. Biology A-level > 6. Core Concepts - Genetic information is copied and passed on to daughter cells > Flashcards

6. Core Concepts - Genetic information is copied and passed on to daughter cells Flashcards

1
Q

chromosome

A

made of DNA, which is wound around histone proteins

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2
Q

chromatin

A

in a cell that is not dividing

chromosomes are unwound single structures and are not visible

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3
Q

centromere

A
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4
Q

when do chromosomes become visable

A

At the beginning of cell division, the chromatin condenses. This means the chromatin coils so tightly that the chromosomes become visible.

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5
Q

chromatids

A

The chromatids in one chromosome are called sister chromatids and are genetically identical.

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6
Q

homologous pairs

A

chromosomes are in homologous pairs

do not have identicle DNA to each other

One of each pair has been inherited from the male parent the other of each pair has been inherited from the female parent

termed homologous because they are the same size and shape and carry the same genes in the same order at the same gene locus (position of the gene on the chromosome).

The alleles (different forms of a gene) can be the same or can be different.

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7
Q

diploid

A

Cells where the chromosomes are paired are termed diploid, these are body or somatic cells.

Diploid cells can divide by mitosis or meiosis.

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8
Q

haploid

A

Cells where the chromosomes are unpaired are termed haploid, these are gametes. Some organisms have body cells that are haploid.

Haploid cells can only divide by mitosis.

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9
Q

order of gene nucleus chromosome dna

A
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10
Q

alleles on homologous chromosomes

A
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11
Q
A
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12
Q
A
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13
Q

diagram of general cell cycle

A
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14
Q

interphase

A

G1, S and G2

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15
Q

S phase part of interphase

A

DNA replication takes place

only happens if the cell is going to proceed to mitosis or meiosis.

Cells that are carrying out their functions are in G1 phase for their lifespan.

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16
Q

mitosis

A

single parent cell divides to produce two genetically identical daughter cells

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17
Q

In interphase, the cell is:

A

synthesising ATP
making new organelles
carrying out protein synthesis
increasing in size
replicating DNA.

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17
Q

cytokinesis

A

Cytokinesis is the division of cytoplasm to form two new cells, each with a nucleus.

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18
Q
A
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19
Q
A

D

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20
Q

The graph below shows how the mass of DNA changes during the cell cycle.

A
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21
Q
A
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22
Q

Mitosis Prophase

A

the chromosomes condense and become visible as two sister chromatids joined by a centromere.

Centrioles migrate to the opposite sides of the cell (the poles).

The spindle begins to form in animal cells only, made by the centrioles.

The nuclear membrane disintegrates and the chromosomes scatter through the cell.

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23
Q

Mitosis Metaphase

A

the spindle completes, and the microtubules go from one side of the cell to the other (from pole to pole).

The chromosomes migrate to the equator of the cell and attach to the spindle fibres by the centromere.

Each chromosome is attached to one spindle fibre.

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24
Q

Mitosis Anaphase

A

the spindle fibres shorten pulling the chromatids to the poles of the cell by the centromeres.

The centromere divides.

Sister chromatids from one chromosome are pulled to opposite poles.

At this point the chromatids are called chromosomes again.

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25
Q

Mitosis Telophase

A

the chromosomes reach the poles of the cell and uncoil.

The spindle fibres break down.

New nuclear membranes form around each set of chromosomes.

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26
Q
A

Metaphase

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27
Q
A

A- centromere

B- spindle fibres

28
Q
A

KLHI
J: Interphase
The cell is preparing for division. Chromosomes are not visible as they are in their uncondensed form, and the cell grows and duplicates its DNA.

K: Prophase
Chromosomes condense and become visible. The nuclear envelope starts breaking down, and the spindle fibers begin to form.

L: Metaphase
Chromosomes align along the metaphase plate (the center of the cell), attached to spindle fibers by their centromeres.

I: Anaphase
Sister chromatids are pulled apart to opposite poles of the cell as the spindle fibers shorten.

H: Telophase
Chromatids reach the poles, and nuclear envelopes begin to reform around the separated chromosomes. The cell starts to divide into two.

29
Q

how is mitosis different
plant vs animals

A
  1. Plant cells lack centrioles, so, although they have a spindle, it is not generated by centrioles.
  2. In animal cells, the spindle degenerates at telophase but in plants it remains as the new cell wall is formed.
  3. At cytokinesis, animal cells form a cleavage furrow where the cytoplasm indents. In plant cells a cell plate forms between the two new nuclei and this develops into the new cell wall.
  4. Mitosis produces two new genetically identical daughter cells, so the cells have the same chromosome number as the ‘parent’ cell.
30
Q

Uses of mitosis

A
  1. Mitosis is used for growth by making new cells, or for repairing tissues by replacing damaged cells. Mitosis happens in a number of different tissues in animals but in plants it is confined to meristematic tissue such as root and shoot tips and the cambium in stems.
  2. Mitosis is also used in asexual reproduction, all the individuals produced are genetically identical.
31
Q

What controls the length of the cell cycle

A

The length of the cell cycle is controlled by genes. If these genes are damaged the cell cycle can be shorter and mitosis is uncontrolled. Uncontrolled mitosis can lead to tumours forming and cancers.

32
Q
A
33
Q

summary mitosis garlic experiment

A
34
Q

microscope view of meristem
10x

A
35
Q

microscope view of meristem
40x

A
36
Q
A

X - ANAPHASE
Z - TELOPHASE
Y - METAPHASE

37
Q

mitotic index

A

The mitotic index is the percentage of cells in a mitotic phase that can be seen at any one time. It is the number of cells visible in prophase, metaphase, anaphase and telophase all together, divided by the total number of cells in the field of view multiplied by 100. A higher mitotic index indicates a faster growth rate.

The mitotic index goes down the further back from the root tip the sample is taken from. In the zone of elongation, the cells are getting longer, which also contributes to growth of the root.

The number of cells at each stage in mitosis can be expressed as a percentage of the total number of cells in the field of view, and if the duration of one cell cycle is known, the time taken for each phase can be calculated.

38
Q

Meiosis is a reduction division

A

this means that the chromosome number is reduced from diploid (2n) to haploid (n).

39
Q

product of meiosis

A

The product of meiosis is a gamete. Gametes fuse at fertilisation, restoring the diploid number.

40
Q

meiosis ensures

A

Meiosis ensures that the chromosome number of individuals remains the same from generation to generation in sexually reproducing populations.

41
Q

how is reduction achieved

A
42
Q

meiosis reasons for genetic differences

A

Each cell is genetically different because of crossing over and random assortment during meiosis.

Random fusion of gametes means that the zygotes and offspring developing from them are all genetically different. This variation means that if environmental conditions change, some of those offspring will have variations that enable them to survive, increasing the chance of survival of the species.

43
Q

crossing over

A
44
Q

independent assortment

A

Mendel stated -
Inheritence of seed shape is independent of inheritence of seed colour

When gametes form the two alleles of any given gene segregate during meiosis independently of any two alleles of the other genes

45
Q
A
46
Q

Meiosis 1
Prophase 1

A

Prophase I: chromatin condenses and chromosomes become visible as two sister chromatids joined by a centromere. Homologous chromosomes pair up forming bivalents. Crossing over between the maternal and paternal chromosomes of the homologous pair takes place at chiasmata. In animal cells, the centrioles migrate to the poles. The spindle forms and the nuclear membrane disintegrates.

47
Q

Meiosis 1
Metaphase 1

A

Metaphase I: the bivalents migrate to the equator of the cell and attach to the spindle by the centromeres. The orientation of the maternal and paternal homologs towards the poles is random, this is random assortment.

48
Q

Meiosis 1
Anaphase 1

A

Anaphase I: the spindle contracts and pulls the chromosomes towards each pole. Each chromosome is still composed of two chromatids, although they are not genetically identical because of crossing over.

49
Q

Meiosis 1
Telophase 1

A

Telophase I: the chromosomes reach the poles and the nuclear membranes reform. Each nucleus is haploid as the chromosomes are not paired.

50
Q

Meiosis 1
Cytokinesis

A

Cytokineses: forms two cells each with a haploid nucleus.

51
Q

diagram of crossing over during Prophase 1

A
52
Q

Meiosis II: in this stage, the daughter cells divide again in two.

A

Prophase II: the chromosomes condense and become visible as two chromatids joined by a centromere. The spindle forms and the nuclear membranes disintegrate.

53
Q

Meiosis II: in this stage, the daughter cells divide again in two.
Metaphase 2

A

Metaphase II: the chromosomes migrate to the equator and attach to the spindle by the centromere. The chromatids are not identical, each one in the chromosome can orientate towards a pole randomly – random assortment.

54
Q

Meiosis II: in this stage, the daughter cells divide again in two.
Anaphase 2

A

Anaphase II: the centromeres divide as the chromatids are pulled to the poles by contraction of the spindle. The chromatids are now called chromosomes.

55
Q

Meiosis II: in this stage, the daughter cells divide again in two.
Telophase 2

A

Telophase II: the chromosomes reach the poles and the nuclear membranes reform.

56
Q

Meiosis II: in this stage, the daughter cells divide again in two.
Cytokinesis 2

A

Cytokinesis: each cell now divides, forming two daughter cells.

57
Q
A

Prophase 1

58
Q
A

Metaphase 1

59
Q
A

Anaphase 2

60
Q
A

Haploid

61
Q
A

Telophase 1

62
Q
A

Random assortment

63
Q

meiosis 10x objective lens

A
64
Q

Using the x40 objective lens focus on a pollen sac and the cells dividing, you will see something like the image below. Draw and label the dividing cells as shown.

A
65
Q
A
66
Q
A
67
Q
A
68
Q

Compare mitosis and meiosis

A
  1. Mitosis takes place in one division, meiosis has two consecutive divisions.
  2. Mitosis produces two genetically identical cells, as identical sister chromatids are separated. Meiosis produces four cells that are not genetically identical because of crossing over in prophase I and random assortment in metaphase I and II.
  3. Meiosis can only happen in diploid cells as the homologous pairs form bivalents in prophase I. The diploid number is reduced to the haploid number. Mitosis can happen in diploid or haploid cells as the sister chromatids from each chromosome are separated into new cells. Haploid cells undergoing mitosis produce haploid cells, diploid cells undergoing mitosis produce diploid cells.

1. Biology A-level (17 decks)

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