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Biology A-level > Mitosis / meiosis > Flashcards

Mitosis / meiosis Flashcards

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1
Q

What type of cell does binary fission occur in?

A

Prokaryotic cells

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2
Q

Describe binary fission (4 points).

A
  1. Bacteria replicate by binary fission.
  2. Replication of circular DNA.
  3. Division of cytoplasm to produce 2 daughter cells.
  4. Each with a single copy of circular DNA.
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3
Q

How do antibiotics work? (4 points).

A
  1. Antibiotics work by inhibiting enzymes that catalyse the formation of murein cross linkages in bacterial cell walls.
  2. These cell walls prevent bacterial cells undergoing osmotic lysis.
  3. Viruses don’t have cell walls- therefore antibiotics are ineffective.
  4. Also, once a virus has entered a body cell, medicines cannot reach the virus.
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4
Q

Definition of mitosis

A

Production of two daughter cells that have the same number of chromosomes as the parent cell and each other. Mitosis occurs in the body cells.

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5
Q

Definition of homologous pairs

A

Two chromosomes that carry the same genes.

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6
Q

Describe interphase as part of the cell cycle (3 points).

A

G1- Synthesis of proteins.
S- DNA undergeos semi-conservative replication
G2- Organelles grow and divide.

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7
Q

State and describe the stages of mitosis (4 points)

A
  1. Prophase- Chromosomes shortena nd thicken to become visible. Chromosomes appear as two sister chromatids joined at the centromere. Nuclear envelope begins to disintegrate and spindle fibres begin to grow from the poles.
  2. Metaphase- Chromosomes line up on the equator. Chromosomes attached to spindle fibres by their centromere.
  3. Anaphase- The centromere splits. Sister chromatids are pulled to opposite poles, as spindle fibres contract.
  4. Telophase- Chromosomes uncoil and become thinner. Cytokinesis begins.
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8
Q

Describe interphase from meiosis (3 points).

A
  1. Chromosomes are dispersed (so not visible).
  2. Each chromosome replicates.
  3. Chromosomes made of 2 sister chromatids, joined at the centromere.
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9
Q

Describe prophase 1 from meiosis (5 points).

A
  1. Chromosomes shorten and thicken to become visible.
  2. Chromosomes appear as two sister chromatids joined at the centromere.
  3. Homologous pairs of chromosomes from bivalents.
  4. Chiasma forms: the point where chromosomes crossover each other.
  5. A new combination of alleles are produced.
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10
Q

Describe metaphase 1 in meiosis (2 points)

A
  1. Homologous chromosome (in bivalents) line up on the equator.
  2. Chromosomes attached to spindle fibres by their centromere.
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11
Q

Describe anaphase 1 in meiosis

A

Homologous chromosomes are pulled to opposite poles.

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12
Q

Describe telophase 1 in meiosis

A

Chromosomes uncoil and become thinner. Cytokinesis begins (sometimes).

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13
Q

Describe prophase 2 in meiosis

A

Chromosomes shorten and thicken to become visible. Chromosomes appear as pair of of chromatids joined at the centromere.

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14
Q

Describe metaphase 2 in meiosis (2 points).

A
  1. Chromosomes line up on the equator.
  2. Chromosomes attached to spindle fibres by their centromere.
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15
Q

Describe anaphase 2 in meiosis

A

Pairs of chromosomes are pulled to opposite poles. Centromere will split.

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16
Q

Describe telophase 2 in meiosis

A

Chromosomes uncoil and become thinner.

17
Q

Describe cytokinesis in meiosis

A

Cytoplasm divides. Membranes form around new cells. 4 haploid cells are produced.

18
Q

WHat is the difference between meiosis 1 and 2?

A

In meiosis 1- homologous apirs of chromosomes are separated. In meiosis 2- pairs of chromosomes are separated.

19
Q

Compare mitosis and meiosis

A
  1. Meiosis reduces the chromosome number and mitosis maintains the same number of chromosomes as in the parent nucelus.
  2. Meiosis chromosomes cross over and there is no crossing over in mitosis.
  3. In meiosis, there are 2 divisions and in mitosis, there is only one division.
  4. In meiosis, the cells produced are genetically different and in mitosis, the cells are gentically identical.
20
Q

What is crossing over?

A

During meiosis 1, the chromatids of each pair of homologous chromosomes become twisted around each other. During this twisting, tensions are created and parts of the chromosomes break off. These broken parts join with the chromatids of its homologous partner. It is the equivalent portions of the chromosomes that are exchznged. New genetic combinations of alleles are produced.

21
Q

What is independent assortment?

A

Each pair of homologous chromosomes will randomly position themsleves on the equator of the cell during metaphase 1. The way in which each pair arranges itself as the equator is totally independent of any other pair.This creates new combinations of chromosomes in the gametes.

22
Q

How does meiosis result in variation?

A

Homologous chromosomes pair up. Independent segration / random assortment. Maternal and paternal chromosomes are re-shuffled in any combination. Crossing over leads to exchange parts of (non-sister) chromatids / alleles between homologous chromosomes. Both create new combinations of alleles.

23
Q

Why is meiosis important in sexual reproduction?

A

Produces haploid cells so fertilsation maintains the chromosome number in next generation. 46 chromosomes in a zygote.

24
Q

Explain a non-disjunction event

A

When homologous pairs of chromosomes fail to separate during meiosis. Usually results in the gamete having either one more or fewer chromosomes. When fertilised with a gamate with a normal complete chromosome number, this will make the fosspring have more or fewer chromosomes than normal. This wil be the same in all their body cells. Example: down syndrome. It is an example of a chromosome mutation. A chromosome mutation changes the structure or number of whole chromosomes. This is different to a gene mutation which is a change in the bas sequence of a gene.

25
Q

What is the cell cycle?

A

An order of events, leading to cell growth and division.

26
Q

What are the stages of the cell cycle?

A

G0: Resting phase
G1: Synthesis of proteins
G2; DNA is replicated.
Nuclear division.
Mitosis.
Cell division.
Cytokinesis.

27
Q

EQU to calculate lenght of time spent in a stage of mitosis

A

(Number of cells in stage) / (total number of cells) x number of hours

Biology A-level (27 decks)

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