Flashcards in Animal Reproduction Deck (31):
What is Asexual Reproduction?
Reproduction leading to genetically identical offspring; no genetic diversity, but energetically inexpensive. A relatively faster process.
What is Sexual Reproduction?
Diploid individuals (2n) produces haploid sex cells (n) [gametogenesis]. Haploid sex cells (n) unit to form new diploid individual [fertilization].
Genetic diversity, energetically expensive and relatively slow.
What is Budding?
Asexual Reproduction - a new individual arises from an outgrowth of an older one. Common in sponges and some Cnidarians.
What is Fission?
Asexual Reproduction - one individual separates into 2 or more individuals of equal size.
What is Fragmentation/Regeneration?
Asexual Reproduction - Individual breaks into small pieces - each piece can form a new individual. Some cells must dedifferentiate.
What is Parthenogenesis?
Asexual Reproduction - Development of an individual from an unfertilized egg, sometimes also called incomplete sexual reproduction.
Common in Arthropods, some fish, amphibians, and lizards.
Can be used for sex determination (e.g. ants, bees, wasps [social insects], females = diploid [fertilization], males = haploid [parthenogenesis]).
What is Cyclic Parthenogenesis?
Some invertebrates alternate between asexual and sexual mode of reproduction depending on the environmental condition.
What is an example of Cycle Parthenogenesis?
Daphnia - conditions favourable = parthenogenesis (female)
conditions unfavourable = sexual-mode of reproduction (male, some females)
What is Hermaphroditism?
A unique form of sexual reproduction.
Synchronous hermaphroditism = earthworm = both male and female characteristics.
Sequential hermaphroditism = reef fish (pseudochromids) = change sex at some point in their life cycle.
Live in an environment dominated by one sex.
What are Protoandrous?
Sequential hermophroditics who were originally male and switched to female.
What are Protogynous?
Sequential hermophroditics who were originally female and then switched to male.
What are Characteristics of Sexual Reproduction?
Increased Genetic Variability -
1. Independent assortment of homologous chromosomes during meiosis 1 (8.3 million combinations)
2. Crossing over during Prophase 1 (mixing of genes)
3. Random Fertilization (70 Trillion combinations)
More chromosomes = more genetic variability.
What is Gametogenesis?
Haploid gametes produced by germ cells in primary sex organs.
What are Eggs?
Female haploid gametes produced by ovaries. Large and non-mobile, done through oogenesis.
What are Sperm?
Male haploid gametes produced by testes, small and mobile. Produced by spermatogenesis.
What is important about Spermatogenesis?
Each diploid parent cell produces 4 sperm cells. Each day, about 3 million primary spermatocytes develop from diploid cells.
What is involved in the Endocrine Control of Spermatogenesis?
The hypothalamus (GnRH) stimulates the anterior pituitary, producing LH and FSH.
LH = Leydig cells (produce, activate, secrete testosterone - indirectly activates spermatogenesis)
FSH = Sertoli cells (directly activates spermatogenesis)
Negative feedback loops are used.
What is important about Oogenesis?
Only 1 ovum is produced in an ovarian cycle. Oogenesis occurs within follicles (layers of tissues).
Full complement of primary oocytes is present at birth and held dormant (in prophase 1) until puberty.
What is involved in the Endocrine Control of Oogenesis and Ovulation?
FSH stimulates one follicle to develop (complete meiosis 1) - estradiol stimulates the growth and development of the oocyte; LH triggers ovulation - progesterone prepares the uterus for receiving the embryo.
FSH increases in the blood - spike in estrogen (estradiol) - LH - triggers ovulation.
Positive feedback control (from first spike of estrogen) to hypothalamus; negative feedback control to pituitary.
What is Fertilization?
Combining two haploid gametes to form a diploid zygote.
What is External Fertilization?
Common in aquatic animals, the haploid gametes are released into the environment, and there they fuse to form a zygote.
There is no risk of desiccation. Potential risks include predation, water currents, and sudden environmental changes; these are compensated by large number of offspring and specific behavioural adaptations.
What is Internal Fertilization?
Common in terrestrial animals, the haploid gametes are released inside the animal and fertilization occurs inside the animals.
What is the Structure of the Mature Sperm?
Head (Nucleus, acrosome - hydrolyzing enzymes)
Mitochondria (produces the ATP that propels the movement of the tail)
Tail (allows sperm to swim)
Very little cytoplasm
What is the Structure of the Mature Ovum?
Zona Pellucida (glycoprotein outer layer, layer that surrounds the plasma membrane)
Cumulus Mass (grows inside a follicle, multiple layers of follicle cells)
What are the general steps of Fertilization?
Haploid egg and sperm unite to form diploid zygote.
Sperm swims toward egg, following species-specific chemical attractant molecules (chemotaxis; drives/guides the sperm toward the egg; high degree of species specificity).
Sperm contact plasma membrane of ova using proteolytic enzymes in acrosome to digest zona pellucida.
Once the sperm fuses with the egg, other sperm are prevented from entering.
What are the general steps of the cellular mechanisms of fertilization?
1. The fertilizing sperm penetrates the corona radiate via membrane-bound enzymes in the plasma membrane of its head and binds to ZP3 receptors on the zona pellucida.
2. Binding of the sperm to these receptors triggers the acrosome reaction, in which the hydrolytic enzymes in the acrosome are released onto the zona pelucida.
3. The acrosomal enzymes digest the zona pellucida, creating a pathway to the plasma membrane of the ovum. When the sperm reaches the ovum, the plasma membranes of the two cells fuse.
4. The sperm nucleus enters the ovum cytoplasm.
5. The sperm stimulates the release of Ca2+ stored in cortical granules in the ovum, which in turn inactivates ZP3 receptors, leading to the block to polyspermy
What makes sure only one sperm fuses?
The inactivation process of the ZP3 receptors makes sure only one sperm fuses with an ovum.
What prevents fertilization of an ovum by the sperm of a different species?
Receptor proteins on ovum prevent fertilization by the sperms of other species; species specificity of sperm-ZP binding.
Long-term stress-response are triggered by steroid hormones secreted by the __ __.
The anterior pituitary gland only secretes __.