Vertebrate Reproduction
- Created by: daisygbates
- Created on: 21-05-17 23:14
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Vertebrate Reproduction
General features
- Timing of sexual maturity
- Environmental factors
- Photoperiod, temperature, breeding sites etc
- Act on hypothalamic-pituitary system
- Hormones control breeding, courtship + gonadal development
Reproduction definitions
- Semelparous - breed once then die
- Iteroparous - 2 or more reproductive cycles in lifetime (most common)
- Associated reproductive pattern - male androgens highest at mating (most common)
- Dissociated reproductive pattern - mating occurs when androgens reduced
- Oviparous - eggs
- Viviparous - live young
- necessitates internal fertilisation
Sex determination
- 3 types
- Genotypic
- Differences in 1 pair chromosomes
- Homogametic sex - chromosomes identical
- 'default'
- Heterogametic sex - chromosomes different
- Requires gonadal steroid hormones to overcome default
- SRY gene - Y chromosome, initiates testosterone release
- Requires gonadal steroid hormones to overcome default
- Sex chromosomes evolved separatelyin birds + mammals
- Temperature-dependant
- High/Low temperature determines sex
- Intermediate temperature = ratio of both sexes
- Oestrogens can reverse 'masculinising temperatures'
- Androgens cannot
- Behavioural
- Hermaphroditism
- Sequential and simultaneous
- EXAMPLE: female saddleback wrasse changes sex if there are too few males present
- Hermaphroditism
- Genotypic
Hypothalamic-pituitary axis
- Ultimate control of reproduction
- Ventral brain
- Hypothalamus - neuro-endocrine organ
- Interface - nervous + endocrine systems
- Receives nerve impulses
- Transduces signal - chemical stimuli
- 2 kinds neuropeptide hormones act on pituitary
- Gonadotropin-releasing hormones (GnRHs)
- Gonadotropin-inhibiting hormones (GnIHs)
- 2 main gonadotropins
- Follicle Stimulating Hormone (FSH)
- Males
- Spermatogenesis
- Females
- Maturation ovarian follicles
- Inhibited by corpus luteum
- If implantation fails, CL degenerates, FSH inhibition stops, follice development restarts
- Males
- Luteinizing hormone (LH)
- Males
- Interstitial cells
- Testosterone inhibits overproduction
- Females
- causes ovulation
- …
- Males
- Follicle Stimulating Hormone (FSH)
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