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Biology > CELL DIVISION > Flashcards

CELL DIVISION Flashcards

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1
Q

What are the main parts of a chromosome?

A

Chromatid and centromere

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2
Q

What are non-sister chromatids?

A

Chromatids from different chromosomes

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3
Q

What are homologous chromosomes?

A

The matching pair of chromosomes from the father’s cell and mother’s cell that have the same length, size and genetic information at the same location in the chromosome.

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4
Q

How many pairs of homologous chromosomes are there in humans, and which are excluded?

A

22 pairs.

The sex chromosome X is longer than sex chromosome Y, hence they are not homologous chromosomes.

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5
Q

What is synapsis?

A

The fusion of homologous chromosomes at the start of meiosis.

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6
Q

What is the chiasma?

A

The point at which paired chromosomes come into contact in the first prophase of meiosis, in order to exchange genetic material between the non-sister chromatids.

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7
Q

Define mitosis.

A

Process by which the nucleus of a cell divides to produce two daughter cells identical to the parent cell.

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8
Q

What is the cell cycle in mitosis?

A

Interphase -> Mitosis -> Cytokinesis

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9
Q

What happens in interphase?

A

Chromosomes in the cell replicate to form two identical sister chromatids joining at the centromere. The centriole replicates.

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10
Q

What are the stages of mitosis?

A

Prophase -> Metaphase -> Anaphase -> Telophase

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11
Q

What happens in prophase?

A
  1. Duplicated chromatin condenses into visible chromosomes
  2. Spindle fibres form in the cytoplasm
  3. Nuclear envelope breaks down into vesicles
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12
Q

What happens in metaphase?

A
  1. Chromosomes align along the equator (middle) of the spindle fibres
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13
Q

What happens in anaphase?

A
  1. Centromeres divide
  2. Sister chromatids separate and move along the spindle fibres to the opposite poles as daughter chromosomes
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14
Q

What happens in telophase?

A
  1. Daughter chromosomes arrive at the poles.
  2. Chromosomes uncoil and lengthen to become thin chromatin threads again
  3. Nuclear envelope reappears around the daughter chromosomes
  4. Spindle fibres disappear
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15
Q

What happens in cytokinesis?

A
  1. The cytoplasm divides
  2. Cell membrane pinches inward ultimately to produce two diploid daughter cells
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16
Q

What are diploid (2n) cells?

A

Cells that have the complete number of chromosomes (46) and are genetically identical to the parent cell.

17
Q

How does mitosis differ in animals and plants?

A

In plant mitosis, the cytoplasm does not pinch inwards during cytokinesis/ Instead, the fusion of vesicles at the equator of the cell forms a cell plate.

A new cell wall is formed along the cell plate between the 2 daughter nuclei, dividing them into two.

18
Q

Why is mitosis important in living organisms?

A
  1. Produces new cells for growth, repair etc
  2. Allows for asexual reproduction in unicellular organisms to form new organisms
  3. Ensures identical genetics of the offspring or new cells to the parent
  4. Preserves the diploid number of chromosomes
19
Q

Define meiosis.

A

Process by which a parent diploid cell divides to produce four daughter haploid cells.

20
Q

What are haploid (n) cells?

A

Cells that contain half the number of chromosomes (23) as the parent nucleus.

21
Q

How is meiosis unique?

A
  1. Produces gametes (eggs and sperm)
  2. Involves a reduction in the amount of genetic material
  3. Comprises two successive nuclear divisions: meiosis I and meiosis II
22
Q

What are the stages of meiosis?

A

Interphase -> Meiosis I -> Meiosis II -> Cytokinesis

23
Q

What happens in prophase I?

A
  1. Duplicated chromatin condenses into visible chromosomes
  2. Homologous chromosomes synapse through synapsis
  3. Crossing over occurs, where chromatids may cross and exchange part of genetic information, giving rise to genetic variations in germ cells
  4. Spindle fibres form in the cytoplasm
24
Q

What happens in metaphase I?

A

Homologous chromosomes align themselves along the equator of the spindle fibres

25
Q

What happens in anaphase I?

A

Paired homologous chromosomes separate from each other, and each moves to the opposite pole of the cell

(Each chromosome contains TWO chromatids)

26
Q

What happens in telophase I?

A
  1. Nuclear membrane forms around the chromosomes at each pole
  2. Cytoplasm divides to form two daughter cells, each containing only haploid chromosome sets
27
Q

What happens in prophase II?

A
  1. Centrioles move to opposite poles
  2. Spindle fibres appear
  3. Nuclear envelope breaks down
28
Q

What happens in metaphase II?

A

Chromosomes align themselves along the equator of the spindle fibres

29
Q

What happens in anaphase II?

A
  1. Centromeres divide
  2. Sister chromatids separate and move along the spindle fibres to the opposite poles as daughter chromosomes
30
Q

What happens in telophase II?

A
  1. Spindle fibres disappear
  2. Nuclear membrane forms around the daughter
31
Q

At which points of meiosis does genetic variation occur?

A

PROPHASE I
- crossing over of chromosomes allows the exchange of genetic materials between the pair of homologous chromosomes

METAPHASE I
- independent assortment of chromosomes, resulting in a random mixture of maternal and paternal chromosomes

FERTILISATION
- random fusion of gametes

32
Q

Why is it important meiosis produces haploid gametes?

A

To enable the restoration of diploid chromosomes in the species when haploid gametes fuse in fertilisation.

Biology (7 decks)

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