Mitosis and Meiosis

Question 1

• What are the main functions of mitosis?

Answer 1

Growth, replacement of dead cells

Question 2

• What are the two major phases of cell division?

Answer 2

Mitotic phase and interphase

Question 3

• What stage of division are cells usually in?

Answer 3

Variable – cells can be in G0 (liver), continually dividing (epithelium), dividing according to regular signals (germ cells), dividing on demand (wound epithelium)

Question 4

• How many chromosomes are present in a diploid cell?

Answer 4

Two homologous copies of each chromosome

Question 5

• What happens during interphase?

Answer 5

DNA is synthesised, centrioles replicate

Question 6

• What are the phases of mitosis?

Answer 6

Interphase, prophase, metaphase, anaphase, telophase

Question 7

• What is control of the cell cycle important for the individual cell?

Answer 7

Damaged DNA must not be replicated, DNA replication must only occur once per cycle, chromosomes must be positioned on spindle correctly, phases of cycle must be synchronous

Question 8

• What are the two levels of cell cycle control?

Answer 8

Intracellular & intercellular

Question 9

• What are Cdks?

Answer 9

Cyclin dependent protein kinases – act as checkpoints at the end of G1, G2 and M phases, regulated by cyclins

Question 10

• What does mitogenic mean?

Answer 10

Stimulates mitogenesis or cell division e.g. growth factors

Question 11

• Growth factors activate Myc, how does the cell prevent excessive production of Myc?

Answer 11

Excessive Myc production activates Arf, Arf activates p53 which induces cell cycle arrest or apoptosis

Question 12

• How does p53 bring about apoptosis?

Answer 12

P53 causes activation of p21, inhibitor of the cell cycle (apoptosis occurs if damage is beyond repair)

Question 13

• Where does meiosis occur?

Answer 13

Germ cells – produces haploid cells that carry one copy of each chromosome

Question 14

• What are the three phases of meiosis?

Answer 14

Meiotic S phase, meiosis I, meiosis II (like mitosis)

Question 15

• When do chiasmata form?

Answer 15

Prophase I

Question 16

• What are the five stages of Prophase I?

Answer 16

Leptotene, zygotene, pachytene, diplotene, diakenesis

Question 17

• At which stage does crossing over occur?

Answer 17

Pachytene

Question 18

• What is significant about prophase II?

Answer 18

No DNA replication occurs

Question 19

• What is the main difference between spermatogenesis and oogenesis?

Answer 19

During the second meiotic division of oogenesis a single haploid ovum and a second polar body (package of chromosomes) are formed

Question 20

• What are the sources of genetic variation?

Answer 20

Independent assortment of chromosomes, recombination – crossing over, mutation, segregation of genes (random), differences in gene frequency (chance)

Question 21

• What method of variation introduces new genes, rather than reshuffling the existing genes?

Answer 21

Mutations

Question 22

• What is independent assortment of chromosomes?

Answer 22

Random orientation of homologous chromosomes a metaphase of meiosis I

Question 23

• In sex chromosomes where does crossing over occur?

Answer 23

Between the short segments at the end of the X and Y chromosomes

Question 24

• In females what happens to the inactive X chromosome?

Answer 24

Condensed as Barr body

Question 25

• What type of mutation can be transmitted to further generations?

Answer 25

Germ line (not somatic)

Question 26

• How might chromosomal abnormalities occur?

Answer 26

Spontaneously or by environmental damage

Question 27

• What are the four possible types of changes that can occur in a chromosomes structure?

Answer 27

Deletion, duplication, inversion, translocation