Week 26 Flashcards
(41 cards)
What are the key differences between oogenesis and spermatogenesis?
- Oogenesis: One gamete formed per stem cell.
Spermatogenesis: Four gametes per stem cell.
Oogenesis has interruptions; spermatogenesis is continuous.
Oogenesis occurs in the ovary; spermatogenesis in the testis.
Oogenesis starts before birth; spermatogenesis starts at puberty.
What are the stages of oogenesis?
- Oogonium → Mitosis → Primary oocyte (2n).
Meiosis I begins before birth, arrested in prophase I.
Completes at puberty → Secondary oocyte (n) + polar body.
Meiosis II starts, arrested at metaphase II. If fertilised: Meiosis II completes → Ovum (n) + 2nd polar body.
What hormonal feedback mechanisms control oogenesis?
- Hypothalamus releases GnRH → Stimulates anterior pituitary to release FSH and LH. FSH: follicle growth. LH: ovulation. Follicle releases oestrogen → negative feedback to hypothalamus. High oestrogen → positive feedback → LH surge → ovulation.
What structures are visible in a cross-section of the ovary?
- Primary follicle (small, single layer). Developing follicle (multiple granulosa layers). Graafian follicle (fluid-filled cavity). Corpus luteum (yellow body). Corpus albicans (degenerate corpus luteum).
What is the process of spermatogenesis?
- Occurs in seminiferous tubules. Spermatogonia (2n) → Mitosis → Primary spermatocytes (2n) → Meiosis I → Secondary spermatocytes (n) → Meiosis II → Spermatids (n) → Maturation → Spermatozoa (n).
Describe the early stages of spermatogenesis.
- Spermatogonia undergo mitosis. Some remain stem cells; others become primary spermatocytes. Primary spermatocytes begin Meiosis I.
What happens after meiosis in spermatogenesis?
- Secondary spermatocytes → Meiosis II → Spermatids. Spermatids → Spermiogenesis: lose cytoplasm, grow flagellum, become spermatozoa.
How is spermatogenesis hormonally regulated?
- Hypothalamus releases GnRH → Anterior pituitary releases LH & FSH. LH → Leydig cells → Testosterone. FSH → Sertoli cells → Support spermatogenesis. Testosterone → Negative feedback to hypothalamus.
What structures are visible in a cross-section of the testis?
- Seminiferous tubules (spermatogenesis). Sertoli cells (support sperm). Leydig cells (interstitial space, secrete testosterone).
What is the structure and function of the seminiferous tubules?
- Lined with germinal epithelium.
Basal layer: spermatogonia.
Luminal layer: spermatids/spermatozoa.
Sertoli cells support and nourish developing sperm.
What are the roles of Sertoli and Leydig cells?
- Sertoli: Blood-testis barrier, nourish sperm, secrete inhibin (inhibits FSH).
Leydig: Between tubules, produce testosterone in response to LH.
What are the key hormones involved in pregnancy?
- hCG: Maintains corpus luteum.
Progesterone: Maintains endometrial lining.
Oestrogen: Stimulates uterine growth.
Hormones produced by placenta after corpus luteum degenerates.
What are the two main types of reproduction in animals?
- Asexual reproduction (offspring genetically identical to parent)
- Sexual reproduction (genetic recombination between two individuals)
What are the costs of sexual reproduction?
- Cost of meiosis: only 50% of genes passed on
- Energy and time spent finding a mate
- Increased risk of predation and disease
- Risk of gametes not finding each other
What is the benefit of sexual reproduction?
- Creates genetic variation, which enables natural selection
- Improves adaptability and survival of species
What is August Weismann’s hypothesis about sex?
- Sex increases variation in gene combinations
- Allows selection to operate more efficiently
What does the Hardy-Weinberg principle state about genetic variation?
- Genetic variation will be maintained in a population under certain conditions (no selection, mutation, migration, or drift)
How does mimicry illustrate the importance of genetic variation?
- Variability in phenotype helps individuals avoid predation by resembling toxic species
How does the sickle cell anaemia example support sexual reproduction?
- Heterozygotes have malaria resistance without disease
- Maintains genetic variation in population
What is the Red Queen hypothesis?
- Constant coevolution with parasites drives the need for genetic variation from sex
How do mud snails support the Red Queen hypothesis?
- Populations with more males (sexual reproducers) are less infected by parasites
Why is behaviour important in sexual reproduction?
- Gametes must meet and timing must be correct
- Behaviour helps attract mates and synchronise reproduction
What behaviours help with successful sexual reproduction?
- Courtship
- Parental care
- Nest building
- Feeding and protecting offspring
What are the different mating strategies in the animal kingdom?
- Monogamy: 1 male, 1 female
- Polygyny: 1 male, multiple females
- Polyandry: 1 female, multiple males
- Promiscuity: multiple partners
- Polygynandry: multiple males & females
