2- sexual reproduction in mammals

Question 1

order of oogenesis

Answer 1

oogonia -> primary oocytes -> first meiotic division -> second meiotic division -> completion of meiosis -> polar bodies

Question 2

oogenesis- oogonia

Answer 2

primordial germ cells divide by mitosis to form oogonia during the foetal period

Question 3

oogenesis- primary oocytes

Answer 3

• each oogonium grows and becomes a primary oocyte
• the primary oocyte enters prophase of the first meiotic division but halts
• at birth, all primary oocytes are in a state of arrested development until puberty

Question 4

oogenesis- first meiotic division

Answer 4

at the start of each menstrual cycle, one primary oocyte resumes its first meiotic division to form a secondary oocyte and a small polar body

Question 5

oogenesis- second meiotic division

Answer 5

• the secondary oocyte enters metaphase of the second meiotic division but halts
• the secondary oocyte is released at ovulation

Question 6

oogenesis- competition of meiosis

Answer 6

• when fertilisation occurs, the secondary oocyte resumes its second meiotic division to form the ovum and another polar body

Question 7

oogenesis- polar bodies

Answer 7

• they are small cells that eventually degenerate
• they serve to discard the extra set of chromosomes

Question 8

spermatogenesis- spermatogonia

Answer 8

primordial germ cells divide by mitosis to form spermatogonia

Question 9

spermatogenesis- primary spermatocytes

Answer 9

spermatogonia grow and become primary spermatocytes

Question 10

spermatogenesis- first meiotic division

Answer 10

primary spermatocytes enter the first meiotic division to form secondary spermatocytes

Question 11

spermatogenesis- second meiotic division

Answer 11

• secondary spermatocytes enter the second meiotic division to form spermatids

Question 12

spermatogenesis- maturation

Answer 12

• spermatids differentiate and grow to form mature spermatozoa

Question 13

polar body

Answer 13

• small cells that bud off from an oocyte which eventually degenerate
• they serve to discard the extra set of chromosomes

Question 14

gonad

Answer 14

the organ that produces gametes

Question 15

germinal epithelium

Answer 15

an epithelium consisting of a single layer of primordial germ cells that undergoes mitosis to produce other cells

Question 16

primordial germ cells

Answer 16

the primary undifferentiated germ cell type that differentiates into germ cells and give rise to gametes through meiosis

Question 17

oogenesis diagram

Answer 17

Question 18

spermatogenesis diagram

Answer 18

Question 19

events of fertilisation order

Answer 19

initial contact -> acrosome reaction -> enzyme release -> membrane fusion -> entry of sperm nucleus -> cortical reaction -> competition of meiosis II -> nuclear fusion

Question 20

fertilisation- initial contact

Answer 20

glycoproteins on the sperms cell membrane and the eggs zona pellucida interact

Question 21

fertilisation- acrosome reaction

Answer 21

the acrosome reaction is triggered. it fuses with the sperms cell membrane

Question 22

fertilisation- enzyme release

Answer 22

the acrosome releases hydrolytic enzymes, which help digest the zona pellucide

Question 23

fertilisation- membrane fusion

Answer 23

the sperms cell membrane and the eggs cell membrane fuse together

Question 24

fertilisation- entry of sperm nucleus

Answer 24

the sperm nucleus enters the egg

Question 25

fertilisation- cortical reaction

Answer 25

the cortical reaction is triggered, cortical granules in the egg fuse with the cell membrane and release enzymes that harden the zona pellucida to prevent polyspermy

Question 26

fertilisation- competition of meiosis II

Answer 26

the egg completes the second meiotic division

Question 27

fertilisation- nuclear fusion

Answer 27

the haploid nuclei of the sperm and ovum to form a diploid nucleus- a zygote

Question 28

egg diagram

Answer 28

Question 29

sperm diagram

Answer 29

Question 30

corona radiata

Answer 30

follicle cells that form a protective coating around the oocyte

Question 31

zona pellucida

Answer 31

- protective coating that the sperm has to penetrate through for fertilisation to occur - prevents polyspermy

Question 32

cortical granules

Answer 32

releases substances which causes the zona pellucida to harden, forming a rough fertilisation membrane

Question 33

nucleus - egg

Answer 33

haploid so a full set of chromosomes is restored at fertilisation

Question 34

acrosome

Answer 34

contains digestive enzymes which break down the zona pellucida and allow sperm to penetrate the egg

Question 35

nucleus- sperm

Answer 35

haploid, so a full set of chromosomes is restored at fertilisation

Question 36

mitochondria

Answer 36

provide energy for rotation of the flagella allowing the cell to move

Question 37

centriole

Answer 37

the centriole is contributed to the zygote to allow it to undergo cell division

Question 38

flagella

Answer 38

allows the sperm to swim towards the oocyte

Question 39

early development of the embryo to blastocyst stage

Answer 39

1) the zygote undergoes mitosis as it moves through the fallopian tube towards the uterus 2) blastomere cells are formed 3) by day 3-4, a morula (solid ball of 16 blastomeres) is formed, it reaches the uterus 4) by day 5-9 a blastocyst (ball is filled with fluid) is formed, cell differentiation begins. 5) the trophoblasts (outer layer of cells) form the amnion, placenta and extraembryonic tissues 6) the inner cell mass (blastomeres) form the embryo