mitosis and meiosis (topic 4)

Question 1

what does mitosis do and what is it used for

Answer 1

cell division in all cells excluding gametes
- 2 daughter cells are genetically identical to parent cells (unless mutation)
important for:
organism growth,
tissue repair/cell replace,
reproduction eg bacteria

Question 2

what is interphase

Answer 2

the period of time cells are not dividing (90% of the time), you can just see the nucleus and cell membrane in a microscope, chromosomes are not visible

DNA replication occurs => 46 chromosomes become still 46 chromosomes due to centromere (92 chromatids)

/ chromosome (one chromatid)
X also chromosome (sister chromatids)

Question 3

mitosis - prophase

Answer 3

chromosomes become visible, condense (short+fat)

nuclear membrane disintegrates

spindle fibres start to develop from centrioles at opposite poles

Question 4

mitosis - metaphase

Answer 4

sister chromatids line up along the equator of the cell because spindle fibres attach to the centromeres and pull them into position

Question 5

mitosis - anaphase

Answer 5

sister chromatids are pulled apart to opposite poles, spindle fibres contract and pull on the centromeres

Question 6

mitosis - telophase

Answer 6

nuclear envelopes reform
chromosomes recoil (long+thin) and become invisible
spindle fibres disintegrate

Question 7

cytokinesis

Answer 7

splitting of cytoplasm => 2 genetically identical daughter cells

Question 8

mitotic index equation

Answer 8

= (P+M+A+T) / total no of cells x100

prophase, metaphase, anaphase, telophase

Question 9

what does chemotherapy aim to do

Answer 9

blocks some part of the cell cycle to stop the growth of the cancer
- prevent dna replication, or metaphase by interfering with spindle formation

Question 10

sex cells chromosomes

Answer 10

have 23 chromosomes each (haploid)

Question 11

meiosis prophase I

Answer 11

nuclear envelope disintegrates and nucleolus disappears
centrioles move to opposite and spindle fibres start to form
chromosomes condense (short and fat) becoming visible
pair up in homologous chromosomes

Question 12

meiosis metaphase I

Answer 12

pairs of homologous chromosomes line up along the equator
crossing over can occur between homologous chromosomes (exchange genetic material)
- recombinant chromosomes are formed

Question 13

meiosis anaphase I

Answer 13

spindle fibres contract, pulling pairs of homologous chromosomes apart to opposite poles

Question 14

meiosis telophase I

Answer 14

nuclear envelope and nucleolus reform
chromosome recoil (long and thin) become invisible

then cytokinesis

Question 15

meiosis prophase II

Answer 15

nuclear envelope disintegrates and nucleolus disappears
chromosomes condense (short and fat) and become visible
centrioles move to opposite poles and spindle fibres form

Question 16

meiosis metaphase II

Answer 16

sister chromatids (chromosomes) line up along the equator (due to spindle fibres attached to centromeres)

Question 17

meiosis anaphase II

Answer 17

spindle fibres contract pulling sister chromatids apart to opposite poles

Question 18

meiosis telophase II

Answer 18

nuclear envelope and nucleolus reform
chromosomes recoil (long and thin) becoming invisible

Question 19

meiosis cytokinesis 2 (product)

Answer 19

4 genetically different daughter cells
each have 23 chromosomes and 23 chromatids (haploid)

Question 20

meiosis - independent segregation

Answer 20

meiosis is random, 2 chromosomes that pair up will randomly mix when gametes form
(metaphase, they could move around which means they get separated into different daughter cells)

Question 21

meiosis - genetic recombination

Answer 21

each pair of chromosomes lie side by side, so genes can cross over

Question 22

calculate possible number of combinations of chromosomes in each daughter cell

Answer 22

(2^n) (n = no of pairs of homologous chromosomes)

eg humans = 2^23 = 8,388,608

after fertilisation: (2^n)^2

Question 23

homologous chromosomes

Answer 23

copies of the chromosome with same size and gene position
=> eg one from mother one from father