Niyogi Lectures 15-17

Question 1

What is budding and what animals is it common in?

Answer 1

Asexual reproduction where a new individual arises from an outgrowth of an older one.
Common in sponges and some cnidarians

Question 2

What is fission and what animals is it common in?

Answer 2

Asexual reproduction where one individual separates into 2 or more individuals of about equal size.
Bacteria and some cnidarians

Question 3

What is fragmentation/regeneration and what animals is it common in?
What may be necessary in this process?

Answer 3

Asexual reproduction where an Individual breaks into small pieces– each piece can form a new individual.
Some cells must dedifferentiate
Starfish

Question 4

Whats is parthenogenesis? What animals is this common in? What purpose does it serve?

Answer 4

Asexual reproduction where the development of an individual arises from an unfertilized egg.
Common in Arthropods, some fish, amphibians, and lizards
Can be used for sex determination like in ants, bees, and wasps
where the females are diploid and males are haploid

Question 5

Some invertebrates alternate between sexual and asexual reproduction based on environmental conditions. Give an example.

Answer 5

Daphnia

Question 6

Compare simultaneous hermaphroditism and sequential hermaphroditism.
Also use the terms protogynous and protoandrous.

Answer 6

Simultaneous hermaphroditism: have both ovaries and testes
sequential hermaphroditism: change sex
Protogynous is female before male
Protoandrous is male before female

Question 7

How does sexual reproduction increase genetic variability? (3)

Answer 7

(1) Independent assortment of homologous chromosomes during meiosis I
(2) crossing over during prophase I
(3) random fertilization

Question 8

What is gametogenesis?

Answer 8

haploid gamete production by germ cells in primary sex organs
- oogenesis (ovaries)
- spermatogenesis (testes)

Question 9

Describe spermatogenesis.

Answer 9

Each diploid parent cell produces 4 haploid sperm cells

Question 10

How does the endocrine system control spermatogenesis?

Answer 10

Sertoli cells provide factors necessary for the successful progression of spermatogonia into spermatozoa. Sertoli cells have receptors for follicle stimulating hormone (FSH) and testosterone which are the main hormonal regulators of spermatogenesis.

Question 11

Describe oogenesis.

Answer 11

Question 12

How does the endocrine system control oogenesis and ovulation?

Answer 12

FSH stimulates one follicle to develop (complete meiosis I
Estradiol stimulates the growth and development of the oocyte
LH triggers ovulation
Progesterone prepares the uterus for receiving the embryo

Question 13

External fertilization occurs mainly in aquatic animals. Why?

Answer 13

Because water is usually needed for the sperm to travel to the egg. Cannot afford to excrete their gametes on the external environment because water is a valued resource; very well may dry up and the gametes could die. This is a massive waste of energy.

Question 14

What are the potential risks of external fertilization? How do animals compensate?

Answer 14

gametes are open to predation risks, may not be viable

Produce massive amounts of gametes or protect the offspring

Question 15

Describe the structure of mature gametes.

Answer 15

Question 16

What are the cellular mechanisms of fertilization?

Answer 16

(1) Acrosome releases hydrolytic enzyme that dissolves the jelly coat of the ovum
(2) sperm-head binds to the receptor on the plasma membrane of the ovum
(3) fusion of sperm and ovum plasma membranes, sperm nucleus enters the ovum
(4) Activation of IP3-Ca2+ signaling pathway, separation and hardening of zona pellucida (fertilization membrane)
(5) fusion of two haploid nucleus to form a diploid nucleus

Question 17

What prevents fertilization of an ovum by the sperm of a different species?

Answer 17

One major barrier that prevents the fusion of isolated gametes from different species is the zona pellucida—a glycoprotein-rich coat that surrounds the ovulated oocyte—which exhibits species-specific interactions with sperm

Question 18

What prevents polyspermy?

Answer 18

An egg must be fertilized by a single sperm only. To prevent polyspermy, the zona pellucida, a structure that surrounds mammalian eggs, becomes impermeable upon fertilization, preventing the entry of further sperm.

Question 19

What is the trade-off of external or internal fertilization/development?

Answer 19

External- less energy
Internal- more protection

Question 20

Define oviparous, viviparous, and ovoviviparous.

Answer 20

Types of internal development/fertilization

Oviparous:
- lay eggs, no support from parent
- evolution of amniotic egg
- birds

Viviparous:
- live young, nutrients, gases, etc. from parent
- most mammals

Ovoviviparous:
- young develop in an egg inside parent often with live birth but little maternal support
- some insects, sharks, snakes

Question 21

Why do fertilized eggs of aquatic animals not have shells?

Answer 21

external fertilization, water environment

Question 22

List the early stages of development following fertilization.

Answer 22

Question 23

Cleavage produces a multi-celled zygote. What does this mean?

Answer 23

Mitotic cell divisions without new cytoplasm or increase in size/mass causes the zygote to be partitioned into successively smaller cells

Question 24

Describe the structure of the morula, the multi-celled zygote produced by cleavage.

Answer 24

Animal pole:
- most active (small cells divide rapidly)
- in some species forms the embryo

Vegetal pole:
- less active (large cells divide slowly)
- may form the yolk

Question 25

Describe the structure of the blastula, the multi-celled zygote produced by further cleavage of the morula.

Answer 25

Blastocoel: fluid filled cavity that will form the coelom (body cavity)

Question 26

The ratio of nuclear volume to cytoplasmic volume in the embryo increases/decreases steadily during cleavage.

Answer 26

increases

Question 27

There is very little gene transcription during cleavage. Why?

Answer 27

chromosomes are condense during all of mitosis and everything is getting copied during S, not much time for transcription

Question 28

How do meroblastic and holoblastic cleavage compare?

Answer 28

Question 29

What is gastrulation?

Answer 29

The continued division and migration of embryonic cells that forms three germ layers (Ectoderm, Mesoderm, and Endoderm) and primordial germ cells (PGC).
Invagination at blastopore forms archenteron (early gut lined with mesoderm).