Gametogenesis

Question 1

What is gametogenesis?

Answer 1

The making of sex cells, spermatogenesis or oogenesis

Question 2

What process is required for gametogenesis?

Answer 2

Meiosis, one parent cell makes for genetically different, haploid daughter cells

Question 3

Where is sperm formed in most species?

Answer 3

Highly specialised organs, gonads

Question 4

Describe spermatogenesis

Answer 4

Sperm are produced from spermatogonial stem cells. Spermatogonial cells divide by mitosis initially, producing the diploid primary spermatocytes. In total, each primary spermatocyte gives rise to four sperm cells

Question 5

Where does spermatogenesis occur in insects and mammals?

Answer 5

Insects = occurs within the cysts in testes 
Mammals = occurs seminiferous tubules in the testes

Question 6

What is the direction of spermatogenesis in insects and mammals?

Answer 6

Insects = from distal to proximal 
Mammals = from periphery to lumen

Question 7

When does spermatogenesis begin in insects and mammals?

Answer 7

Insects = starts in larval stage 
Mammals = From puberty

Question 8

How long does spermatogenesis last in insects and mammals and how many sperm are produced per day??

Answer 8

Insects = Produced in a few days, 10 000 per day
Mammals = Produced in 74 days, 300 000 000 per day

Question 9

Where is sperm stored in insects and mammals?

Answer 9

Insects = Stored in the seminal vesicle
Mammals = Stored in epididymis for <4 weeks or reabsorbed

Question 10

Where does semen come from in insects and mammals?

Answer 10

Insects = Semen from accessory glands
Mammals = semen from seminal vesicles and prostate glands

Question 11

What is sperm gigantism?

Answer 11

Sperm length exceeds body length

Question 12

What is sperm heteromorphism?

Answer 12

The simultaneous production of two or more distinguishable types of sperm by a single male

Question 13

What is oogenesis?

Answer 13

A primary oocyte gives rise to a single oven, begins in the female embryo

Question 14

Where does oogenesis occur in insects and mammals?

Answer 14

Insects = From distal to proximal
Mammals  = Within a follicle

Question 15

How long oogenesis last in insects and mammals and how many are produced per day?

Answer 15

Insects = Starts in larval stage, eggs are produced in a few days <100 eggs per day
Mammals  = 400 000 follicles at birth and no more are produced, but ovulation begins in puberty, one egg per month produced

Question 16

Where are eggs released into in insects and mammals?

Answer 16

Insects = released into uterus for fertilisation
Mammals  = Follicle ruptures, oocyte enters fallopian tube for fertilisation

Question 17

What happens if an egg isn’t fertilised in mammals?

Answer 17

If not fertilised, degenerates and prepared uterus lining (thick, vascular endometrum lining) sloughs away

Question 18

What controls gametogenesis?

Answer 18

Hormones. At puberty, hypothalamus secretes gonadotrophin- releasing hormone (GnRH)
GnRH stimulates FSH (follicle stimulating hormone) and LH (lutenizing hormone) from the anterior pituitary cells.

Question 19

How do FSH and LH affect spermatogenesis?

Answer 19

FSH – stimulates development of seminiferous tubules (where sperm form) and spermatogenesis acting together with testosterone by stimulating Sertoli cells
LH – stimulates Leydig cells to secrete testosterone which stimulates spermatogenesis

Question 20

How do FSH and LH affect oogenesis?

Answer 20

FSH – stimulates development of follicles and secretion of estrogens
LH – stimulates maturation of follicles and release of ova at ovulation

Question 21

What is the role of oestrogen and progesterone

Answer 21

Estrogen – enhances growth of follicles, grows endometrium
Progesterone – grows and maintains endometrium for pregnancy, secretes nutrients for embryo
Fluctuate in 28 d cycle in humans

Question 22

What do embryonic placental cells secrete if fertilised?

Answer 22

chorionic gonadotropin to rescue the corpus luteum and maintains its function

Question 23

How does the birth control pill work?

Answer 23

By negative feedback to FSH and LH

Question 24

When does menstruation occur?

Answer 24

When oestrogen and progesterone levels are low