,WEEK 1
1.1 INTRODUCTION TO REPRODUCTION
Appreciate how knowledge of reproduction system is applied in veterinary profession
Appreciate the differences between sexual and non-sexual reproduction
Outline the key characteristics and stages of meiosis, and how meiosis differs from mitosis.
Outline why meiosis is important in sexually-reproducing organisms
Discuss how meiosis is related to the stages of male and female gametogenesis
Define the terms homologous chromosome, homologous recombination, chiasma(ta), crossover, synapsis
Importance of reproduction
➢ Fertility decreasing in humans and animals
➢ Milk yield increasing, fertility decreasing in cows
What can reduce fertility?
➢ Pollution, deforestation, rising global temp
➢ Migration disruption
Biological reproduction = The process by which new individuals are produced from previously existing individuals.
Asexual Reproduction
- One individual producing genetically identical offspring to itself
- Produced by mitosis
Types
- Budding = offspring grows out of body of parent
- Gemmules = parent releases specialised mass of cells that develop into offspring
- Fragmentation = body of parent breaks into pieces
- Regeneration = piece of parent detaches and grows into new individual
Sexual Reproduction
- Two individuals produce offspring with genetic characteristics from both parents
- Introduces new gene combinations into populations
Advantages + disadvantages
- Allows for genetic variation and in turn natural selection to occur
- Allows a species to be more competitive
- Two parents require
- Only half of parent genes passed on (meiosis)
- Reproduction rates are less efficient
2 chromatids per chromosome → attached by a centromere
Haploid (n)
Diploid (2n)
Locus = Position of gene
What are homologous chromosomes?
➢ Pair of chromosomes similar in shape and size
➢ Carry genes controlling same inherited traits
➢ Each locus is in same position
Meiosis for males (spermatogenesis)
➢ Spermatogonia undergo mitosis > provide stock of cells
➢ Spermatogonia enter meiosis > form spermatocytes
➢ Spermatocytes undergo 2 division rounds > form 4 haploid spermatids
, ➢ Spermatids differentiate into > spermatozoa
Meiosis during female gametogenesis
➢ Oogonia expand by mitosis > provides stock of egg precursors
➢ Oogonia enter meiosis I > forming oocytes
➢ DO NOT progress to meiosis II until ovulation occurs (sperm enters egg)
Interphase: Before meiosis begins, genetic material is duplicated.
First division of meiosis
Prophase 1: Duplicated chromatin condenses and forms chromosomes. Each chromosome consists of two, closely
associated sister chromatids. Crossing-over can occur during the latter part of this stage.
Metaphase 1: Homologous chromosomes align at the equatorial plate.
Anaphase 1: Homologous pairs separate with sister chromatids remaining together.
Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of the
homologous pair.
Second division of meiosis: Gamete formation
Prophase 2: DNA does not replicate.
Metaphase 2: Chromosomes align at the equatorial plate.
Anaphase 2: Centromeres divide and sister chromatids migrate separately to each pole.
Telophase 2: Cell division is complete. Four haploid daughter cells are obtained
Homologous Recombination
➢ Exchange of identical DNA sequences between similar/identical DNA molecules
1) Double strand breaks in both DNA molecules
2) DNA strands exchanged and repaired (crossing over)
3) Crossing sites known as chiasma (like a chain)
Non-disjunction
➢ Failure of chromosomes or chromatids to separate during meiosis
➢ Results in odd chromosomes number (1 less Monosomy , 1 more Trisomy)
, 1.2 NON-PREGNANT FEMALE ANATOMY AND PHYSIOLOGY
Identify key components of the female reproductive system (e.g. ovaries, oviducts, uterus, cervix, vagina,
vestibule, associated ligaments).
Describe the gross anatomical structures of the ovary and their respective functions.
Describe the histological features of follicles at different stages of development and relate these to the
process of folliculogenesis, oogenesis, ovulation and luteolysis.
Folliculogenesis
Development of follicle from primordial follicle to corpus luteum
➢ Provides hormonal and structural support to oocyte
Primordial follicle
- Dormant until puberty
- Immature & smallest
- Single layer of flattened cells (squamous epithelium)
Primary follicle
- Single layer of cuboidal cells (granulosa cells)
Secondary follicle
- Has microscopic Theca cells
- 2+ layers of follicular cells
- Oocyte surrounded by thick zona pellucida layer
Early Antral/tertiary follicle
- Fluid filled space (antrum)
- Surrounded by Theca externa
Dominant Antral follicle
- Large fluid filled space
- Oocyte on edge of granulosa cells
- Cumulus granulosa
What happens to follicle during ovulation
1) Wall breaks down, ruptures through ovary into oviduct
2) Blood vessels rupture = corpus haemmorragicum
3a) Becomes corpus luteum = secreted progesterone
3b) Becomes corpus albican = egg not fertilised
Oogenesis = development of the oocyte from immature oocyte to ovum
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