Reproduction 1 Flashcards
Define reproduction
production of offspring
Describe 3 key features of asexual reproduction
- All offspring are genetically identical (clones)
- Copying and proliferation in both unicellular + multicellular
- Transmission of an intact, single parental genome but mutations also transferred
Is asexual reproduction widespread across the animal kingdom? Give some examples
Yes it is. e.g komodo dragons, sponges, bees/wasps etc.
Some organisms can reproduce both sexually (when conditions are favourable) & asexually (when they are unfavourable) e.g Daphnia
List the 4 types of asexual reproduction
- Fragmentation/regeneration
- Binary fission
- Budding
- Parthenogenesis
Define fragmentation/regeneration as a type of asexual reproduction
parent broken into pieces = adults, followed by regeneration e.g starfish
Define budding
Offspring grows out of the parent. Specialised masses of cells are released from the parent that can develop into offspring e.g Hydra
Define Parthenogenesis
Virgin birth. Unfertilised eggs develop into offspring but are not haploid. Occurs in several fish, insects, reptiles but NOT mammals due to genomic imprinting
In a low stress environ, will an animal reproduce asexually or sexually?
Asexually
In a high stress environ, will an animal reproduce asexually or sexually?
Sexually
Why do organisms produce sexually in high stress environments (as opposed to asexually)
Because it promotes genetic variation in offspring if environ is unfavourable (stressful)
What is the main con of asexual reproduction?
Parental mutations are passed to offspring –> no genetic variation
What are the 3 stages of sexual reproduction?
- Gametogenesis
- Mating
- Fertilisation
Define gametogenesis
production of gametes
- evolutionarily conserved
Define mating
transferring of gametes
- extraordinarily diverse
Define fertilisation
fusion of gametes
- evolutionarily conserved
What are the 2 stages of gametogenesis?
- Meiosis (diploid cell → haploid cell)
- Spermatogenesis and oogenesis
Describe spermatogenesis
- Produced from spermatogonial stem cells → divide by mitosis initially = diploid primary spermatocytes
- 1 primary spermatocyte = 4 sperm cells
Describe spermatogenesis in mammals
- Occurs in seminiferous tubules within testes
- From periphery to lumen
- Starts in puberty
- Sperm produced in approx. 74 days
- Stored in epididymis for <4 weeks or reabsorbed
- Semen from seminal vesicles & prostate gland
Describe spermatogenesis in insects
- Occurs in cysts within testes
- From distal to proximal (outside to centre)
- Starts in larval stage
- Sperm produced in a few days
- Stored in seminal vesicle
- Semen from accessory gland
Gametogenesis: at puberty the hypothalamus secretes what?
GnRH
What does GnRH do?
Stimulates FSH and LH from anterior pituitary cells
What does FSH stand for?
Follicle stimulating hormone
What does FSH do in ‘males’?
stimulates development of seminiferous tubes (where sperm form) & spermatogenesis acting together with testosterone by stimulating Sertoli cells
What does LH stand for?
luteinizing hormone
What does LH do in males?
stimulates Leydig cells to secrete testosterone which stimulates spermatogenesis
Describe sperm morphology
- Head (nucleus)
- Neck (sperm centriole for tail formation and movement, and embryo development)
- Midpiece (mitochondria → ATP for energy)
- Tail (propels sperm forwards)
Give an example of sperm gigantism
fruit fly body length = 3mm/ sperm length = 60mm
