L16: Development of multicellular organisms

Question 1

What cells are egg & sperm derived from?

Answer 1

Germ cells

Question 2

What happens to germ-cell formation during Day 6.25 (pre-gastrulation)?

Answer 2

Primordial germ cells is seen in proximal epiblast pre-gastrulation, where germ layers form

Question 3

What happens to germ-cell formation during Day 7.25 (during gastrulation)?

Answer 3

During gastrulation, the PGC move to the posterior side of the embryo

Question 4

What happens to germ-cell formation during Day 8.5 (post-gastrulation)?

Answer 4

PGC migrate back to embryo

Question 5

Why does PGC express a different combination of genes to somatic cells?

Answer 5

Needed for cell migration & adhesion

Question 6

Define gonads

Answer 6

Glands that produce hormones involved in reproduction

Question 7

Process of PGC reaching to differentiate into eggs or sperm?

Answer 7

PGC enter hindgut endoderm & migrate via dorsal mesentery to reach the genital ridges

Question 8

Why does PGC remain in initial location?

Answer 8

Exclude them from process of laying down body plan and selecting the healthiest

Question 9

How is the migration path of PGC controlled ?

Answer 9

Chemical signals in the environment

Question 10

Define meiosis

Answer 10

Gametes with half the number of chromosomes are produced, zygote will have correct number of chromosomes

Question 11

How many rounds of cell division needs to occur in meiosis to produce 4 haploid cell from 2 diploid cell?

Answer 11

2

Question 12

2 cell divisions of meiosis?

Answer 12

1) Chromosomes replicated before 1st cell divison so number is halfed

2) Prophase: replicated homologous chromosomes pair up to undergo recombination

Question 13

Define diploid

Answer 13

One set of chromosomes

Question 14

Define haploid

Answer 14

2 sets of chromosomes

Question 15

Define oogenesis

Answer 15

Formation of female gametes

Question 16

Define spermatogenesis

Answer 16

Formation of male gametes

Question 17

Pre development of primary oocyte

Stages of oogenesis

Answer 17

1) PGC stays in posterior end of embryo
2) Migrate back inside
3) Enter ovaries
4) Primary oocytes developed

Question 18

When does 1st meiotic divison occur in oogenesis?

Answer 18

Not completed until after the ovulation in the adult

Question 19

When does 2nd meiotic divison occur in oogenesis?

Answer 19

After fertilisation

Question 20

What happens during oogensis after the PGC enters the ovary?

Answer 20

1) Oogonia divide within the ovary and divide into primary oocytes
2) They enter meiosis in embryo but arrested in prophase of 1st meiotic division until ovulation of the adult
3) After ovulation, the secondary oocyte is developed
4) 2nd meiotic division is completed after the secondary oocyte undergoes fertilisation

Question 21

Pre birth

Stages of spermatogenesis

Answer 21

1) PGC goes back into embryo & enter testes
2) Arrest in G1 stage (early stages of mitotic cell cycle)
3) Resume after birth

Question 22

What happens during spermatogenesis after birth?

Answer 22

1) After birth, stem cells are produced by mitosis
2) In a sexually mature animal, spermtogonial stem cells give rise to differentiating spermatocytes

Question 23

Hypothesis to explain mammalian fetal ovarian germline death

Answer 23

1) Failure of meiotic recombination
2) Apoptosis (cell death)

Question 24

Structure of the sperm

Answer 24

Head:
- Acrosome
- Nucleus

Midpiece:
- Centrosome
- Mitochondria

Tail:
- Plasma membrane
- Flagellum

Question 25

Function of acrosome

Answer 25

Enzymes to digest protective coat around egg

Question 26

Function of plasma membrane

Answer 26

Proteins that bind to egg & facilitate entry

Question 27

Function of flagellum & mitochondria

Answer 27

Flagellum: Movement
Mitochondria: Energy

Question 28

Define capacitation

Answer 28

Facilitating fertilisation when the sperm has been deposited into the female reproductive tract

Question 29

What happens during capacitation?

Answer 29

Membrane remodelling & removal of certain inhibitory factors

Question 30

Stages of fertilisation of a mammalian egg

Answer 30

1) Sperm penetrates sticky layer of hyaluronic acid & somatic follicle cells
2) Binds to zona pellucia
3) Pentrates it
4) Plasma membrane of sperm fuses with egg plasma membrane
5) Sperm nucleus enters egg cytoplasm

Question 31

What is zona pellucida?

Answer 31

Layer of fibrous glycoproteins that surround the plasma membrane of the egg

Question 32

What is the wave that stops multiple sperm perpetrating the egg?

Answer 32

Calcium wave

Question 33

Function of the calcium wave at fertilisation

Answer 33

Fertilising sperm triggers calcium wave
- Hardens the outer layer of the egg

Question 34

Describe cortical granule exocytosis

Answer 34

1) High concentrationof Ca2+ causes cortical granule membrane to fuse with the egg membrane

Question 35

Why does a bud in hydra appear?

Answer 35

Due to repeated mitotic division of epidermal intestinal cells

Question 36

What is parthenogenesis?

Answer 36

Development of an embryo from an unfertilised egg cell

Question 37

3 types of bees

Answer 37

1) Worker bees (female)
2) Drone bees (male)
3) Queen bee (female)

Question 38

Characteristics of the worker bees

Answer 38

All female
- Have a reproductive system including a set of ovaries but non-functional

Question 39

Characteristics of the queen bee

Answer 39

Has a functional reproductive system and working ovaries

Question 40

What does the food contain that is fed to worker bees that suppresses ovary growth?

Answer 40

Phenolic Acids

Question 41

What fertilisation system does bees have to reproduce?

Answer 41

Haploid-diploid sex determination system

Question 42

What eggs are females & males produced from?

Answer 42

Females: Sexually from fertilised diploid eggs

Males: Unfertilised haploid eggs