Component 2: Mitosis and Meiosis

Question 1

What is mitosis?

Answer 1

A type of cell division which produces genetically identical daughter cells with each cell containing the same number of chromosomes as the parent nucleus

Question 2

What is mitosis needed for?

Answer 2

• Growth
• Cell replacement and regeneration
• Asexual Reproduction

Question 3

Describe processes in interphase in mitosis?

Answer 3

• DNA replicates, chromosomes are not visible as chromatin is still dispersed
• cell grows in size
• organelles replicate
• proteins (e.g. histones) and enzymes are synthesised

Question 4

Describe prophase in mitosis?

Answer 4

• chromosomes condense (2 chromatids held together by a centromere)
• nucleolus and nuclear envelope disappear
• centrioles move to opposite poles of the cell and start to form spindle fibres

Question 5

Describe metaphase in mitosis?

Answer 5

• chromosomes arrange themselves on the equator of the spindle
• spindle fibres attach to the chromosomes by their centromeres

Question 6

Describe anaphase in mitosis?

Answer 6

• centromeres divide in two
• spindle fibres shorten and pull the chromatids to the opposite poles of the cells, centromere first
• chromatids now called daughter chromosomes

Question 7

Describe telophase in mitosis?

Answer 7

• daughter chromosomes reach the poles, then uncoil and lengthen (become chromatin)
• nuclear envelope and nucleolus reform
• 2 new nuclei are formed
• spindle fibres disintergrate

Question 8

Describe cytokinesis in mitosis?

Answer 8

• DNA appears as chromatin again as chromosomes have uncondensed
• the division of the rest of the cell (cytoplasm and organelles) after the nucleus divides
• in animal cells the cytoplasm pinches in
• in plant cells a cell plate forms

Question 9

What happens after mitosis and cytokinesis?

Answer 9

The cell returns to interphase and continues to grow and perform regular cell activities

Question 10

What is cancer in terms of mitosis?

Answer 10

• uncontrolled mitosis

- cancerous cells divide repeatedly forming a tumour (an irregular mass of cells)

Question 11

What does cancer do to the body?

Answer 11

cancerous cells prevent normal cells/organs from functioning normally

Question 12

What are cancers thought to be started by?

Answer 12

When changes occur in the genes that control cell division

Question 13

What is meiosis?

Answer 13

cell division that occurs during sexual reproduction when it’s important that haploid gametes are produced

Question 14

What does meiosis produce?

Answer 14

• four genetically different cells from 2 consecutive divisions (gametes)
• contain half the original number of chromosomes

Question 15

Define diploid?

Answer 15

Cells or organisms that have two copies of each chromosome in their nuclei, has homologous pairs of chromosomes

Question 16

Define haploid?

Answer 16

A cell or organism that has one set of chromosomes/one copy of each chromosome, doesn’t have homologous pairs of chromosomes

Question 17

What is the diploid number in human?

Answer 17

46 (23 homologous pairs, one from mother and one from father)

Question 18

What are homologous chromosomes?

Answer 18

pair of chromosomes that have the same genes at the same loci (1 maternal and 1 paternal)

Question 19

What happens in interphase?

Answer 19

• chromosomes are not visible
• DNA replicates
• Protein synthesis
• ATP production
• new organelles formed
• mitochondria and chloroplasts replicate
• nuclear envelope and nucleolus still present

Question 20

What happens in early prophase I?

Answer 20

• chromosomes condense from chromatin
• each chromosome consists of 2 sister chromatids held together by a centromere
• centrioles move to opposite poles of the cell
• each homologous pair of chromosomes come together to form a bivalent

Question 21

What happens in late prophase I?

Answer 21

• crossing over takes place between the non-sister chromatids in the bivalent
• the exchange of genetic material (alleles) between homologous chromosomes occurs at the chiasmata forming between chromatids
• nuclear envelope and nucleolus disappear

Question 22

What happens in metaphase I?

Answer 22

• bivalents arrange themselves on the equator of the spindle
• spindle fibres attach to centromere
• chromosomes arrange themselves randomly arrange themselves (random/independent assortment)

Question 23

What happens in anaphase I?

Answer 23

spindle attaches to the centromere of each homologous chromosomes and pulls whole chromosomes to opposite poles as spindle fibres shorten

Question 24

What happens in telophase I?

Answer 24

• (in animals cells) organelles and cytoplasm divide (cytokinesis)
• two new haploid cells are formed (each cell has one copy of each homologous pair)
• chromosome number per cell is halved
• chromosomes are genetically different from those in the original cell
• nuclear envelope reforms
• plants cells go straight to meiosis II, cytokinesis doesn’t take place

Question 25

What happens in prophase II?

Answer 25

- centrioles replicate - new spindle fibres form at right angles to the first - nuclear envelope and nucleolus disappear

Question 26

What happens in metaphase II?

Answer 26

- chromosomes align themselves randomly on the equator of the (90º to original) - each chromosome is a pair of chromatids - this phase produces genetic variation due to the random assortment of chromatids on the equator

Question 27

What happens in anaphase II?

Answer 27

- centromeres divide | - chromatids pulled to opposite poles of the cell by the attached spindles

Question 28

What happens in telophase II?

Answer 28

- cytokinesis begins - four haploid cells result - each daughter cell produced in genetically different - nuclear envelope and nucleolus reappear - chromatids lengthen and become chromatin

Question 29

Describe processes that happen to produce genetic variation

Answer 29

- during independent assortment of homologous chromosomes, maternal and paternal chromosomes are mixed up - during sexual reproduction, there is a random fusion of haploid gametes to form zygote - during crossing over, parts of homologous chromosomes may be exchanged producing new allele combinations

Question 30

Difference between mitosis and meiosis: number of nuclear divisions

Answer 30

mitosis: 1 nuclear division meiosis: 2 nuclear division

Question 31

Difference between mitosis and meiosis: number of cells formed

Answer 31

mitosis: 2 daughter cells formed meiosis: 4 daughter cells formed

Question 32

Difference between mitosis and meiosis: ploidy of parental cells/nuclei

Answer 32

mitosis & meiosis: 23 pairs of chromosomes (2n, diploid)

Question 33

Difference between mitosis and meiosis: ploidy of daughter cells/nuclei

Answer 33

mitosis: diploid meiosis: haploid (produces cells with half the original number of chromosomes)

Question 34

Difference between mitosis and meiosis: genetic nature of daughter cells/nuclei

Answer 34

mitosis: genetically identical daughter cells formed meiosis: genetically different daughter cells

Question 35

Difference between mitosis and meiosis: pairing of homologous chromosomes

Answer 35

mitosis: no pairing of homologous chromosomes meiosis: pairing of homologous chromosomes

Question 36

Difference between mitosis and meiosis: crossing over

Answer 36

mitosis: no crossing over meiosis: crossing over occurs

Question 37

Difference between mitosis and meiosis: segregation of homologous chromosomes

Answer 37

mitosis: homologous pairs aren't separated meiosis: homologous pairs are separated

Question 38

Where is DNA found and what is its function?

Answer 38

Found in the nucleus and controls all cell activities

Question 39

What is chromatin?

Answer 39

Long and thread-like DNA in a non-dividing cell

Question 40

What is a chromosome?

Answer 40

- doubled, coiled, short DNA in a dividing cell - chromosomes only become visible when chromatin condenses prior to cell division - the 2 copies of the chromosome are called sister chromatids and are joined at the centromere

Question 41

Why does chromatin condense?

Answer 41

DNA changes from chromatin to chromosome for more efficient division

Question 42

What is a chromatid?

Answer 42

One of the 2 identical copies of a chromosome, joined at the centromere prior to cell division

Question 43

What is the centromere?

Answer 43

Specialised region of a chromosome where 2 chromatids join and to which the microtubules of the spindle attach at cell division

Question 44

What is meant by homologous?

Answer 44

The chromosomes in a homologous pair are identical in size and shape and they carry the same gene loci, with genes for the same characteristics. One chromosome of each pair come from each parent, X and Y are not homologous

Question 45

What are the 4 stages in the cell cycle?

Answer 45

Mitosis G1 phase S phase G2 phase

Question 46

What happens in G1 phase?

Answer 46

- first growth phase - protein synthesis - cytoplasm increases - number of organelles increases

Question 47

What happens in S phase?

Answer 47

DNA replicates if cell is going to divide

Question 48

What happens in G2 phase?

Answer 48

- second growth phase | - proteins necessary for cell division are synthesised