DNA and Inheritance

Question 1

What happens during nuclear division in somatic cells (mitosis and meiosis) and cytoplasmic division (cytokinesis)?

Answer 1

Eukaryotic cells pass on their instructions for growth and development from 1 generation of cell to the next.

Question 2

How many daughter cells do mitosis and cytokinesis result in?

Answer 2

2 daughters cells (identical sets of chromosomes)

Question 3

Define cell cycle?

Answer 3

The sequence of events from one cell division to another.

The length of the cell cycle varies in different cells

Question 4

What are the 5 phases of mitosis?

Answer 4

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

Question 5

What are the 3 phases in interphase?

Answer 5

G₁ phase

S phase

G₂ phase

Question 6

What occurs during G₁ phase?

Answer 6

Cell metabolically active

Duplicates organelles and cytosolic components

Starts replicating centrosomes

Question 7

What occurs during S phase?

Answer 7

DNA is replicated

Question 8

What occurs during G₂ phase?

Answer 8

Cell growth continues

Enzymes and other proteins are synthesised

Replication of centrosomes is complete

Question 9

What occurs during prophase?

Answer 9

Chromosomes condense and become visible

Spindle fibres emerge from the centrosomes

Nuclear envelope breaks down

Nucleolus disappears

Question 10

What occurs during metaphase?

Answer 10

Mitotic spindle is fully developed

Centrosomes are at opposite poles of the cell

Chromosomes are lined up at the metaphase plate

Each sister chromatid is attached to a spindle fibre

Question 11

What occurs during anaphase?

Answer 11

Cohesin proteins binding sister chromatids together break down

Sister chromatids (now called chromosomes) are pulled towards opposite poles

Question 12

What occurs during telophase?

Answer 12

Chromosomes arrive at opposite poles and begin to de-condense

Nuclear envelope material surrounds each set of chromosomes

The mitotic spindle breaks down

Question 13

What occurs during Cytokinesis?

Answer 13

Animal cells-a cleavage furrow separates daughter cells

Plant cells-a cell plate separates daughter cells

Question 14

Define metacentric.

Answer 14

Centromere in the centre

Question 15

Define submetacentric.

Answer 15

Centromere nearer to one end than the other

Question 16

Define acrocentric.

Answer 16

Centromere close to one end

Question 17

Define telocentric.

Answer 17

Centromere on the end

Question 18

Define apoptosis.

Answer 18

Aprogrammed series of events that lead to cell death as a result of dismantling of the internal contents of the cell (DNA shredded) by various enzymes including caspases

Question 19

Define phagocytes.

Answer 19

Scavenging cells that clear apoptotic bodies.

Particularly macrophages.

Question 20

What problems arise if apoptosis fails?

Answer 20

Cancer

Developmental defects

Question 21

What occurs during apoptosis?

Answer 21

Programmed death is signalled

Cell volume decreases

Membrane bulges outward

Nucleus fragments as cell destroys it

Apoptotic bodies form

Apoptotic debris is engulfed by macrophage

Question 22

How does cytokinesis occur in plant cells?

Answer 22

Cytoplasm of plant cells divides with the formation of a cell plate

Cellulose is deposited at cell plate forming a wall that divides the parent cell into 2 daughter cells – each with a plasma membrane

Question 23

How does cytokinesis occur in animal cells.

Answer 23

Cytoplasm divides by cleavage

Plasma membrane around the middle of cell draws together to form a cleavage furrow

Cleavage furrow continues until edges meet and cell is cleaved (results in 2 daughter cells)

May result in unequal distribution of proteins (asymetrical cell division)

Question 24

Describe binary fission.

Answer 24

Produces 2 daughter cells

Produces the same number of chromosomes as parental cell

Question 25

Why do prokaryotes undergo binary fission?

Answer 25

Lack nucleus Single chromosome with no centromere Not considered proper mitosis

Question 26

What occurs during binary fission?

Answer 26

DNA replicates (2 chromosomes) Each copy attaches to a different part of the cell membrane When cell pulls apart, original and replicate chromosomes are separated A wall forms across the cell and divides into 2 cells of identical genetic composition

Question 27

Where does meiosis occur?

Answer 27

Specialised organs of sexually reproducing animals and plants

Question 28

What does meiosis produce?

Answer 28

Gametes (sex cells) – sperm and egg/ ova 4 daughter cells

Question 29

What occurs during prophase I?

Answer 29

Chromosomes condense, nucleolus disappears & spindle forms with centrioles at opposite ends Homologous chromosomes lie side by side (synapsis) A pair of chromosomes (1 maternal & 1 paternal) now called a bivalent

Question 30

What occurs during metaphase I?

Answer 30

Nuclear envelope breaks down Homologous chromosomes move together to equator of spindle

Question 31

What occurs during anaphase I?

Answer 31

Maternal & paternal chromosomes of homologous pairs move to opposite poles of spindle. The separation or disjunction of each pair of homologous chromosomes occurs independently

Question 32

What occurs during telophase I?

Answer 32

Spindle breaks down, cell starts to separate across its middle & nuclear envelopes form around the 2 new nuclei

Question 33

What occurs at the end of meiosis I?

Answer 33

A brief interphase DNA does not duplicate during this interphase

Question 34

What occurs during prophase II?

Answer 34

New spindle forms at right angles to the first one

Question 35

What occurs during metaphase II?

Answer 35

Chromosomes move to equator of spindle

Question 36

What occurs during anaphase II?

Answer 36

Chromatids separate and move apart from each other Chromatids become the chromosomes of the daughter cells When they reach the poles, the cells enter telophase

Question 37

What occurs during telophase II?

Answer 37

Spindle apparatus disappears Chromosomes de-condense to their thread-like form New nuclear envelopes and nucleoli form

Question 38

Compare function of mitosis and meiosis.

Answer 38

**Mitosis** * Nuclear & cell division for growth, repair & replacement of tissues **Meiosis** * Nuclear & cell division for producing sex cells (gametes)

Question 39

Compare the locations in which mitosis and meiosis occur.

Answer 39

**Mitosis** * Takes place in somatic cells **Meiosis** * Takes place in gonads or reproductive organs (e.g. ovaries & testes of mammals; ovaries & anthers of flowering plants)

Question 40

Compare outputs of mitosis and meiosis.

Answer 40

**Mitosis** * Two cells are the outputs **Meiosis** * Four cells (gametes) are the outputs

Question 41

Compare number of cell divisions in mitosis and meiosis.

Answer 41

**Mitosis** * One cell division completes the process **Meiosis** * Two cell divisions complete the process

Question 42

Compare the number of chromosomes in each daughter cell in mitosis and meiosis.

Answer 42

**Mitosis** * Each daughter contains the diploid (2n) of chromosomes **Meiosis** * Each daughter contains the haploid (n) of chromosomes

Question 43

Compare the way in wich organisms reproduce using mitosis or meiosis.

Answer 43

**Mitosis** * Asexually reproducing organisms reproduce by mitotic division of cells * Prokaryotes reproduce by binary fission not mitosis **Meiosis** * Sexually reproducing organisms reproduce by fusion of gametes, restoring the diploid number (2n) of chromosomes of each cell

Question 44

Compare the amount of variation produced my mitosis and meiosis.

Answer 44

**Mitosis** * New cells of this kind show no variation unless mutations or environmental influences (genetically identical – clones) * Variation & diversity of offspring are narrowed **Meiosis** * Offspring produced show variation between them * Variation and diversity of offspring are increased

Question 45

Compare the applications of mitosis and meiosis.

Answer 45

**Mitosis** * Tissue culture (skin grafts & cloning plants) **Meiosis** * Creating new varieties of organisms