mitosis/meiosis

Question 1

what is mitosis?

Answer 1

cell division which occurs in eukaryotic organisms. in which the maternal cell divides to form 2 genetically identical daughter cells. allows replacement, growth, repair of lost cells and so on…

Question 2

mitosis passes through 6 phases what are these?

Answer 2

• interphase
• prophase
  -> prometaphase
• metaphase
• anaphase
• telophase
• cytokinesis

Question 3

what is interphase

Answer 3

cell going about its normal business
G1 -
S DNA is duplicated (synthesised) during this phase
G2

Question 4

what is prophase

Answer 4

DNA condenses to become chromosomes which are visible under a microscope. centrioles move to opposite ends of the cell and extend microtubules out. (mitotic spindle) the centromeres at the centre of the chromosomes also begin to extend fibres outwards

Question 5

prometaphase?

Answer 5

• nuclear membrane disappears, microtubules attach centrioles to centromeres and start pulling the chromosomes

Question 6

metaphase?

Answer 6

chromosome becomes aligned in the middle of the cell

Question 7

anaphase?

Answer 7

chromosome pairs split (centromeres) are cut and one of each pair (sister chromatids) move to either end of the cell

Question 8

telophase

Answer 8

sister chromatids reach opp ends of the cell and become less condensed and no longer visible, new membranes form around the new nuclei for the daughter cells

Question 9

cytokinesis

Answer 9

an actin ring around the centre of the cell shrinks and splits the cell in two

Question 10

interphase

Answer 10

cell going about normal daily business
preparing for and doubling its DNA to form pairs of chromosomes

Question 11

if there is an error in mitotic division what can that mean for new daughter cell?

Answer 11

• the error will be carried on to that cell
• an error in one cell can go on and be a error in a huge no of cells. chromosomal damage e.g. trisomy 21 -> down syndrome

Question 12

what happens during meiosis?

Answer 12

• a single cell divides twice to form 4 new cell
• these cells have half the normal no of chromosomes (haploid)
• method of producing spermatozoa and oocytes
• when an egg is fertilised by a sperm the chromosomes will combine to form a cell with the normal no of chromosomes

Question 13

meosis I?

Answer 13

first division of meosis
during meosis I a cell passes through phases v similar to those of mitosis but w significant differences - but w some significant differences

Question 14

at the end of meosis I how many chromosomes does each cell have?

Answer 14

23 chromosomes and each chromosome has 2 chromatids (haploid)

Question 15

what is the key event of meosis I?

Answer 15

separation of homologous chromosomes, rather than the separation of sister chromatids as occurs during mitosis.

also in meosis I prophase I stage there is homologous recombination whereby the homologous chromosomes exchange DNA

Question 16

what are homologous chromatids?

Answer 16

two chromosomes that make up the pair of chromosomes that we talk about in diploid cells
they are described as containing genes for the same biological features however the genes may be slightly different

Question 17

female sex hormones are homologous but the male sex chromosomes are not true or false

Answer 17

true

Question 18

does DNA replicate from meosis I to meosis II?

Answer 18

no it does not. therefore there is no interphase therefore they are 2 haploid cells to begin with

Question 19

anaphase in meosis II

Answer 19

chromosome pairs are split (centromeres cut) one of each pair (sister chromatids) moving to either end of the cell (haploid)