chapter 14 - new body cells / sex cells

Question 1

what is mitosis

Answer 1

• occurs in somatic body cells, two daughter cells are produced (2n diploid) which are identical to each other and the parent cell
• function: provide cells for growth, maintenance and repair
• cell cycle: continuous cycle of stage we (interphase, prophase, metaphase, anaphase, telophase)

Question 2

what happens during interphase

Answer 2

• dormant phase between cell division, DNA / nucleus / centriole duplication (46->92 chromosomes), DNA is invisible (long chromatin threads)

Question 3

what happens during prophase

Answer 3

• nuclear membrane and nucleolus break down / disappear
• centrioles: become visible, form miotic spindles in which microtubules radiate (forming spindle fibres), move to opposite poles
• chromatin: threads of DNA become more tightly coiled (visible), are now called sister chromatids (joined at centromere), pairs migrate to equator

Question 4

what happens during metaphase

Answer 4

• chromatid pairs line up at equator, spindle fibres bind to centromere

Question 5

what happens during anaphase

Answer 5

• sister chromatids separate at centromere (become chromosomes), move towards opposite poles, spindle fibres retract towards poles, cell stretches / extends towards poles

Question 6

what happens during telophase

Answer 6

• chromosomes uncoil (no longer visible, become chromatin threads), spindle fibres disappear, nuclear membrane and nucleolus reappear / reform
• cytokinesis: cleavage furrow forms (cleavage: name given to cytoplasmic division), furrow deepens until the cell is split into two (daughter cells form)

Question 7

what is cell division

Answer 7

• function: the process by which new cells are made due to the damage of other cells, to enable growth or for reproduction
• types: mitosis (growth and repair) and meiosis (reproduction)

Question 8

what is meiosis

Answer 8

• occurs in gametes (sperm and ova) in the male and female sex organs, four daughter cells are produced (unique / different to each other and parent)

Question 9

what is fertilisation

Answer 9

• fusion of sperm and egg (form a zygote), daughter cells produced in meiosis (MII) contain half the number of chromosomes (n haploid)
• IPMAT and PMAT (two processes)

Question 10

what is gametogenisis

Answer 10

• gamete formation from meiosis to mature gametes

Question 11

what is spermatogenisis

Answer 11

• occurs in male, seminiferous tubules, formation of 4 spermatozoa (sperm)
• puberty: primary spermatocyte undergo 1st meiotic division to produce secondary spermatocytes undergo 2nd meiotic division to produce 4 (n) spermatids
• everyday: eventually mature into spermatozoa (sperm), cytoplasm is lost and tail forms

Question 12

what is oogenisis

Answer 12

• occurs in female, ovaries, formation of 1 ova and 3 up to polar bodies
• born with all eggs: primary osteocyte undergo prophase 1
• puberty: complete 1st meiotic division to produce a secondary osteocyte and a polar body (1/2 cytoplasm, may undergo 2nd meiotic division, may disintegrate) begins 2nd meiotic division, but stops at metaphase 2
• ovulation: secondary osteocyte is expelled into uterine tubes
• fertilisation: meiosis 2 is completed and produces 2nd polar body and an ootid (n) which matures to become an ovum

Question 13

what happens during meiosis 1

Answer 13

• I1: DNA duplication etc
• P1: chromatin becomes visible, more tightly coiled (chromatid pairs), move to find homologous pairs (same shape, size and gene) consists of 4 strands, crossing over occurs, rest the same
• M1: homologous pairs of random assortment line up at equator
• A1: homologous pairs seperate (1 member = 2 sister chromatids), resulting in 23 sister chromatids (n)
• T1: cytoplasm divides, 2 diploid (2n) cells produced

Question 14

what happens during meiosis 2

Answer 14

• meiosis 2 is the same process as mitosis
• no interphase (no replication of DNA)
• four haploid (n) daughter cells are produced

Question 15

what are factors affecting variation

Answer 15

• random assortment of chromosomes (M1)
• crossing over (P1)
• which egg / spermatids is fertilised
• different partners

Question 16

summary of mitosis

Answer 16

• one duplication of chromosomes, one nuclear division, one process (IPMAT)
• produces 2 diploid (2n) daughter cells, identical to each other and parent cell
• purpose: growth, maintenance, repair
• no homologous pairs, no crossing over, no random assortment
• 46 -> 92 -> 46 + 46

Question 17

summary of meiosis

Answer 17

• one duplication, two nuclear divisions, two processes (IPMAT, PMAT)
• produces 4 haploid daughter cells unique to each other and parent cell
• purpose: formation of gametes for reproduction
• homologous chromosomes pair up and crossing over occurs (P1) and random assortment of chromosomes takes place (M1)