Reproduction Flashcards
Asexual or clonal reproduction mechanisms
Fission, budding, fragmentation
Some reproduce via an egg but without fertilisation e.g. bees and aphids - parthogenesis
Sexual reproduction
Creates genetic variation via fusing of gametes produced during meiosis.
Competitive advantage of 2 parents so that at least some offspring will grow and reproduce in a changing environment.
Strategies used to ensure evolutionary fitness
Synchronisation of gamete release to increase chances of fertilisation
Allow competition to determine sexual selection between males for the same female
External fertilisation, risks and strategies
Sperm must swim to egg, that uses attractants. Risks:
Waves may separate gametes
Strategies: vast numbers, cycles of breeding, amplexus where male clings to female and squeezes out eggs through cloata
Oviparous
e.g. hens lay eggs and monotremes i.e. mammal produce milk but oviparous e.g. duck-billed platypus - all food within egg
Viviparous
e.g. humans, give birth to live young after being growth in mother, eutherian placental animals (real placenta) and marsupials which give birth to live young and have mammary glands by no true placenta so babies born at a much less developed stage
Ovoviviparous
e.g. some fish, lizards, amphibians, snakes
Retain fertilised egg in body but all nutrients from egg not mother
Strategies to ensure survival and competition
Brown garden snails have courtship displays involving shooting love darts into each other that increase sperm counts
Sea urchins get together in large groups to mate - kin selection in close knit communities - look after others if relates -> altruistic
No parental care = more offspring
Lots of parental care = fewer offspring
Monogamy
One partner at a lime, often for life, e.g. birds
Promiscuous
Free for all, male investment low. Live in large groups - kin selectin
Polyandry
Rare - 1 female and many males e.g. mole rats
Polygamy
Males mate with more than one female - 80% mammals, intense male competition - female has most investment
Haremes
e.g. seals = element of female choice, but also competition between males e.g. peacocks shiny bright feathers - shiny if healthy
Sexual dimorphism
Differences in size and colour increase mating success to attract mate and support egg production. Include different appearance of genders for identification, bigger bodies female for eggs and antlers, showing off and other males that isn’t herd
Simultaneous hermaphroditism
Both mature egg and sperm in same organic, - can choose which one but cant fertilise themselves, increasing chance of success
Sequential hermaphroditism
A change from one gender to another (only one at a time) - protogynous = female first; protandrous = male first
Levels of sex determination
Genetic - recomb of X and Y
Gonadal - testes or ovaries present determined by Y chromosomes
Phenotypic - apparent anatomic sex not always true
Congenital adrenal hyperplasia
Inherited enzyme problem in biosynthesis of cortisol. The deficient of 21 beta-hydroxylate leads to a reduction in cortisol and build up of androgen steroid precursor from adrenals - masculinised features of a female
The Guevedoces of Dominican republic
Born looking female, then develop a scrotum and penis at puberty due to a deficient of 5-paha reductive which is the active precursor in production of testosterone.
When does sexual differentiation take place in development?
Early. Biopotential gonad has outer cortex and inner medulla. Sex determination depends on pre scene of SRY gene - TDF activates additional genes (testes), testes produce AMH, DST and testosterone.
Gonads
Pair of testes in male, ovaries in female
Function - produce gametes
Reproductive tract
System of specialised ducts for transporting or housing gametes
Accessory sex glands
Produce supporting secretions into tract
In males…
testes, accessory = seminal besicales, bulbourethral glands, prostate gland, penis, tract = epididymis, bas dederens, urethra
