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
In females…
Ovaries, tract = oviducts (fallopian tubes), uterus, cerix, vagina, vulva
Gametogenesis
The production of gametes is under complex endocrine control. Sex steroid hormones derived from cholesterol.
Glands for production of sex hormones
Hypothalamus, pituitary, gonads
Hypothalamopituitarygonoadal axis
Pulsatile release of GnRH from hypothalamus causes secretion of LH and FSH from pituitary which act on testes to bring about testosterone production -> spermatogenesis
Testosterone
95% from testes, 5% adrenal glands in males. Acts on reproductive system before emirs to masculinise tract and promote decent of testes into scrotum. Has effects on sex-specific tissues after birth - puberty, spermatogenesis an maintenance of tract.
Secondary sexual characteristics: male hair growth, deep voice, muscle growth
Develops sex drive and controls gonadotropin
Promotes bond growth and epiphyseal fusion, causes aggression
Spermatogenesis
Mitotic and meiotic division and cytodifferentiation. Highly specialised (tail, many mitochondria, acrosome) to carry genetic material considerable distance. Spermatozoa krrp close association with sertoli cells during development. 1 spermatogonim:4 spermatozoa.
Sperm stored and concentrated in epididymis and ducts deferens.
During ejaculation…
Sperm mixed with secretions from accessory glands. Seminal vesicles - fructose for energy and prostaglandins providing movement. The prostate alkaline fluid neutralises acid in vaginas and clots so sperm doesn’t fall out. PSA breaks down clot after so sperm can move up (mucous production). Release of sperm in a sexual response cycle: excitement, plateau, orgasmic and resolution phases
Oestrogen
Causes ova maturation and female secondary sexual characteristics. Also has effects on endometrium and myometrium. Feedback on pituitary gonadotrophins.
Progesterone
Effects on endometrium and myometrium (in uterus). Feedback on pituitary and gonadotrophins. Also thermogenic (makes temp rise)
Follicular cycle
Primordial follicles begin to enlarge. Day 6 - one dominant remains and some artertic follicles. Oestrogen secreted to circulation from theca internal cells and follicular fluid from granulose cells. Day 14 = ovulation.
Luteal phase
Proliferation of granulose and theca cells giving luteal cells - corpus luteum. Secretion of oestrogen and progesterone and degradation of CL - corpus albicans
Menstruation
Day 1-5, proliferative phase including endometrium (little secretion), build up day 5-14
Secretory phase
Including vascularisation, coiled glands and secretion of fluid to nature egg day 14-28
Uterine endometrium
Glands enlarge. Stratum functional, coiler arteries, straum basal straight basilar arteries, loss of hormonal support (CL) - thinning of endometrium, spasm of arteries, necrosis and sloughing
Clinical tests for ovulation
Endometrial biopsy (sample of uterus lining), cervical mucous changes, body temp, hormone levels (LH kits - peak just before ovulation, enzyme immunoassays that detect hormone and mid-luteal progestogens - tells you ovulation has occurred)
Hormonal control
Hypothalamus - GnRH brings about anterior pituitary LH and FSH
LH surge caused by switch of oestrogen feedback from- to +. After ovulation = progesterone increase prevents further +ve feedback from oestrogen on LH
Primary oocytes
Remain in meiotic arrest until puberty. At the start of each cycle, a few primary oocytes begin to develop, but usually only 1 ovulate per cycle. Natural loss = atresia. 1 oocyte:1ovum. Antrum formation changes shape. What is left of follicles becomes corpus luteum, which provides hormones to keep fertilised egg going. No fertilisation = death of CL
Specialised features of eggs
Stored nutrients and factors needed for early embryo development. Egg coat - vitelline coat blocks polyspermy by hardening once fertilised. Chemotaxis attacks sperm tp egg. Protein reasct released by arbacia
Drosophila
Produce 1 sperm 3x length of body which blocks female tract so no other males can mate
Cast and marmosets
Spines present on penis so that female is locked to male
Dragonflies
Spoon shaped end to penis to scoop out sperm from another male
Elephants
Reproductive tract ~2m long, testes internal
Males produce sperm from 10-15 years of age - only large bulls can produce
Males has musth - episode of elevated testosterone and aggressiveness with eat-waving musth scent, rumble low frequency noise and musth walk. A cycling female may vocalise and show interest for bulls
Bulls test cow’s readiness to breed by performing flemen behaviour - trunk brings urine samples to receptors in roof of mouth => 1 -3 day window
Cows reproduce from 12-14 years and interval between calves is ~5 years
