Lecture 22- Asexual and sexual reproduction Flashcards
What are the three types of asexual reproduction?
Budding, regeneration, reparthenogenesis
How does budding and regeneration produce new individuals?
Mitosis
How does budding work?
A bud grows by mitosis, cells differentiate before the bud breaks away
What is regeneration?
- Usually replacement of damaged tissues
- Sometimes pieces of an organism can regenerate complete organisms
In what organisms can regeneration be seen?
Echinoderms- each piece including central disk can regenerate
Colonial cnidarians such as corals- pieces broken off in a storm start new colonies
Segmented marine worms break apart
What is parthenogenesis?
The development of offspring from unfertilized eggs
When is parthenogenesis common?
Arthropods, fish, amphibians and reptiles
What can parthenogenesis determine?
Sex- for example, bees:
- Male are haploid
- Females are diploid
What happens in some species where the parthenogentic reproduction requires sexual behavior?
Females may act as males depending on cyclical hormonal states (estrogen and progesterone)
The sexual activity stimulates the release of the egg
What process produces haploid gametes through meiotic cell division?
Gametogenesis
What are the three fundamental steps of sexual reproduction in animals?
Gametogenesis (making gametes)
Mating (bringing gametes together)
Fertilization (fusing gametes)
What are the disadvantages of sexual reproduction?
- Time and energy
- Exposes to predators/damage
- Detracts from other behaviors
What does sexual reproduction require?
Joining of two haploid cells to form a diploid individual
Where does gametogenesis occur?
In the gonads- the testes and ovaries
What are the different gametes?
- Small, motile sperm
- Nonmotile ova (eggs)
What are gametes produced from?
Germ cells
Where do germ cells come from?
They are produced early in the development of the embryo and remain distinct from the rest of the cells
Other than germ cells, what are other embryonic cells called?
Somatic cells
What happens to the germ cells when gonads begin to form?
They migrate to the gonads
Once germ cells are within male gonads, what happens?
They undergo mitosis to produce spermatogonia
After germ cells have migrated into female gonads, what happens?
They undergo mitosis to produce oogonia
What happens to diploid spermatogonia and oogonia?
They multiply by mitosis to produce primary spermatocytes and primary oocytes
What is the next step in gametogenesis after the formation of spermatocytes and oocytes?
Meiosis- reduces chromosomes (haploid cells)
These cells mature into sperm and ova
During spermatogenesis, what does the first and second meiotic division produce?
Two secondary spermatocytes
Four haploid spermatids
During division of primary spermatocytes, what are the offspring connected by?
Cytoplasmic bridges
What happens to spermatids?
They differentiate into sperm
What is the first step in oogensis?
The female germ cell divides by mitosis to form oogonia and then primary oocytes
What happens to the primary oocyte?
It immediately begins prophase I of meiosis
What happens after prophase I of meiosis?
Development stops in many species
What happens after development of the primary oocyte stops?
It grows larger and acquires nutrients
What happens when meiosis resumes?
The nucleus of the oocyte divides into two daughter cells of unequal size
What is the name of the two unequal daughter cells produced by the meiotic division of the primary oocyte?
Secondary oocyte (larger cytoplasm) First polar body (smaller one)
What happens to the secondary oocyte?
It continues with meiosis to form a haploid ootid which differentiates into a mature ovum
And a second polar body which degenerates
What is fertilisation?
The union of a haploid sperm and a haploid egg to create a diploid zygote
What are the 6 steps in fertilisation?
- Recognition of sperm and egg
- Activation of sperm
- Plasma membranes fuse
- Additional sperm entry blocked
- Activation of egg
- Egg and sperm nuclei fuse
How are interactions between sperm and eggs mediated?
Specific recognition molecules
What do specific recognition molecules ensure?
The sperm goes towards the egg
The egg isn’t fertilised by the wrong species
Where is it particularly important eggs aren’t fertilised by the wrong species?
Aquatic organisms where sperm and eggs are released to surroundings
What adaptation do sea urchins have to make sure fertilisation occurs correctly?
Chemical attractants to increase sperm mobility are species specific
Protective layers
What two protective layers must sperm pass to get to the egg in marine animals such as sea Urchins?
A jelly coat
Vitelline envelope
What is an the membrane enclosed structure on the sperm head?
The acrosome
What happens when egg and sperm make contact?
Substances in the jelly coat trigger an acrosomal reaction
What happens during the acrosomal reaction?
Membranes in the sperm head and acrosome break down, enzymes are released and digest the jelly coat
After a hole has been digested in the jelly coat, what happens?
Actin is polymerized, the acrosomal process extends down from the head of the sperm
What is the acrosomal process coated with?
Bindin
A specific recognition molecule
Why is the acrosomal process coated with bindin?
Bindin reacts with bindin receptors in the vitelline envelope
What happens after bindin binds to bindin receptors?
Sperm and egg membranes fuse to form a fertilisation cone.
Internal fertilisation involves…
Specieis specific mating behaviors and egg sperm recognition molecules
What is the mammalian egg surrounded by?
Cumulus- cells in a gelatinous matrix
What is beneath the cumulus?
The zona pellucida- a glycoprotein envelope functionally similar to the vitilline envelope
What happens once sperm has fused and entered an egg cell?
Polyspermy is blocked
Mechanisms prevent entry of more than one sperm to an egg
