Gametogenesis

Question 1

What is a gamete?

Answer 1

The cells responsible for reproduction - sperm and ova - these are haploid cells derived as a product of meiosis containing half the normal amount of DNA and they fuse together to form a diploid zygote

Question 2

How does genetic variation occur?

Answer 2

genetic variation ensures each gamete is genetically unique

• crossing over
• independent assortment
• random segregation

Question 3

What are the differences between men and women in regards to their fertility?

Answer 3

women only have about 400 ova in a lifetime - they are present at birth but are stimulated by fertilisation
men produce a large number or sperm (200 million) per day so their reproductive potential is pretty much unlimited

Question 4

Where does spermatogenesis occur?

Answer 4

seminiferous tubules

Question 5

Why are spermatifus at different levels of maturation at different sections of the seminiferous tubules?

Answer 5

if all were at the same stage then men would need to wait until fill maturation - and as women are only fertile for short periods of time this is not beneficial for fertilisation

Question 6

What is the spermatogenic cycle?

Answer 6

the length of time it takes for spermatids at the same stage in the cycle to show up again when looking at a specific point along the seminiferous tubules

Question 7

What is the spermatogenic wave?

Answer 7

to distance between groups of spermatids at the same level of maturation

Question 8

What is spermiogenesis?

Answer 8

the process by which spermatids become spermatozoa

Question 9

When does spermiogenesis take place?

Answer 9

once the spermatids have been released into the lumen of the seminiferous tubules

Question 10

What happens to the spermatozoa as they pass down the seminiferous tubules?

Answer 10

they remodel as the pass through the retentions testis to mature - non motile spermatids become mobile by the time they reach the epidydimis

Question 11

How do spermatids move if they aren’t mobile?

Answer 11

peristaltic contractions and secretions by the sertoli cells

Question 12

Why do sperm need mitochondria?

Answer 12

they need energy (ATP) and use fructose as their metabolic fuel - flagella tail provides motility for the sperm

Question 13

What do the seminal vesicles secrete?

Answer 13

AA, citrate, fructose, prostaglandins

Question 14

Why is fructose used instead of glucose?

Answer 14

to reduce competition with bacteria

Question 15

What do the prostatic glands produce?

Answer 15

proteolytic enzymes and zinc - less zinc more fertility

Question 16

What do the coppers glands produce?

Answer 16

mucoproteins to help lubricate and neutralise acidic urine in distal urethra

Question 17

What is sperm capacitation?

Answer 17

final maturation step required before sperm becomes fertile

Question 18

Where does capacitation occur and why?

Answer 18

in the female genital tract as the conditions there stimulte;

• removal of glycoproteins and cholesterol fro sperm membrane
• activation of sperm signalling pathways
• allow sperm to bind to zone pellucid of oocyte and initiate acrosome reaction

Question 19

What is oogenesis?

Answer 19

the process of oocyte maturation in the ovary

Question 20

Where do germ cells come from?

Answer 20

arise from the yolk sac

Question 21

How is an oocyte transported?

Answer 21

the fimbrae sweep over the surface of the ovary and the uterine tube begins to contract rhythmically so the oocyte is carried to the tube by the swelling movements of the frimbriae - oocyte then propelled by peristaltic muscular contractions of the tube and by cilia in the mucosa

Question 22

How is an oocyte transported?

Answer 22

the fimbrae sweep over the surface of the ovary and the uterine tube begins to contract rhythmically so the oocyte is carried to the tube by the swelling movements of the frimbriae - oocyte then propelled by peristaltic muscular contractions of the tube and by cilia in the mucosa

Question 23

What happens to the CL if no fertilisation occurs?

Answer 23

the CL degrades and forms a mass of fibrotic scar tissue called the corpus albicans - progesterone production decreases so menstruation follows

Question 24

What happens to the CL is fertilisation occurs?

Answer 24

HCG produced by the embryo prevents CL degenerating and the CL grows to form the CL of pregnancy which secretes progesterone until the placenta becomes adequate to secrete it itself