BIOLOGY

• Asexual reproduction


  • Production of offspring whose genes all come from one parent without the fusion of egg and sperm
  • Usually diploid eggs are produced by mitosis which then develop directly
• Sexual reproduction


  • Production of offspring by the fusion of haploid gametes (eggs & sperm) from two parents to form a diploid zygote (fertilized egg)
  • Dioecious
  • Gametes arise by meiosis
  • Genetic variability is increased by the random combinations of genes from the parents
• Parthenogenesis


  • Development of an embryo from an unfertilized egg or one where sperm & egg nuclei did not fuse
  • Ameiotic parthenogenesis - no meiosis, egg is formed by mitosis (diploid)
  • Meiotic parthenogenesis - haploid ovum formed by meiosis, it may be activated by a male (or not)
• Honey bees: drones are males and are produced parthenogenetically and female workers and queens form from fertilized eggs
• Sexual reproduction


  • Generally involves two parents
  • Special germ cells unite to form a zygote
  • Recombines parental characters
  • Results in a richer, more diversified population
  • In haploid asexual organisms mutations are expressed and selected quickly
  • In sexual reproduction a normal gene on the homologous chromosome may mask a gene mutation
• Hermaphroditism


  • An organism has both male and female reproductive systems
  • Monoecious
  • Some can fertilize themselves
  • Usually a mate is required - they can fertilize each other
• Sequential hermaphroditism


  • An individual reverses its sex during its lifetime
  • In wrasses, sex reversal is associated with age, size and social conditions
  • Fish are female first
  • The largest female becomes male if the previous male dies
  • Protogyny: first female - a change from female to male
  • Protandry: first male - a change from male to female
• Fertilization


  • Fusion of egg and sperm into a single diploid cell, the zygote
  • External
  • Internal
• External fertilization


  • Fertilization takes place outside the female's body
  • A wet environment is required so gametes don't dry out and so sperm may swim to the eggs
  • Environmental cues (day length, temperature) or chemical cues may cause a whole population to release gametes at once to increase likelihood of fertilization
• Internal fertilization


  • Allows terrestrial animals to reproduce away from water
  • Cooperative behavior leading to copulation is required
• Pheromones


  • Chemical signals released into the environment by one organism that influence the physiology or behavior of members of the same species
  • Effective in very small amounts
  • Mate attractants
• Species with external fertilization


  Produce huge quantities of gametes that result in lots of zygotes, but predation on young is high and few will survive to reproduce
• Species with internal fertilization


  Produce fewer zygotes, but protect them more from predation with tough eggshells, embryo development in reproductive tract of female, and parental care of eggs & offspring
• Advantages of sexual reproduction


  • Costs include finding mates, greater energy cost, reduced proportion of genes passed on to offspring, and slower population growth
  • However, increases variability in the population - important during times of environmental change
• Reproductive patterns


  • Oviparous - animals that lay eggs
  • Ovoviviparous - animals that retain the eggs within their bodies, nourishment comes from the egg
  • Viviparous - eggs develop in oviduct or uterus, nourishment from mother
• Invertebrate reproductive systems

  • Many insects have separate sexes, internal fertilization and have complex reproductive systems
  • Female crickets use long ovipositors to deposit eggs
• Vertebrate reproductive systems


  • Nonmammalian vertebrates usually have one combined opening, the cloaca, for the digestive, excretory, and reproductive systems
  • The uterus is partly or completely divided into two chambers in most vertebrates
  • Humans & other mammals with few young, birds & snakes have a single structure
• Reproductive system


  System of sex organs within an organism which work together for the purpose of sexual reproduction
• Primary sex organs


  • Testes in males
  • Ovaries in females
• Gametes


  Sex cells (sperm - male, ova/eggs - female)
• Hormones


  Affect maturation, development and changes in the activity of the reproductive system organs
• Reproductive hormones


  • Estrogen and progesterone in female
  • Androgens (esp. testosterone) in male
• Male reproductive system


  • Testes
  • Ducts
  • Accessory glands
  • Supporting structures
• Follicle-Stimulating Hormone (FSH)


  The pituitary gland makes FSH that is necessary to produce sperm (spermatogenesis)
• Testes


  Primary reproductive organs of the male, produce sperm and secrete hormones
• Primary hormones that help the male reproductive system function


  • Luteinizing Hormone (LH)
  • Testosterone
• Sperm production


  1. Seminiferous tubules in testes

  2. Epididymis for maturation

  3. Vas deferens for transport
• Luteinizing Hormone (LH)


  The pituitary gland also makes LH which is also necessary to continue the process of spermatogenesis
• Epididymis


  Tightly coiled tubes where sperm maturation happens
• Testosterone


  It is the main sex hormone in male. It helps you develop certain characteristics, including muscle mass and strength, fat distribution, bone mass and sex drive (libido)
• Vas deferens


  Passageway for sperm
• Estrogen


  Developing female sexual characteristics
• Ejaculatory duct


  Union of vas deferens and seminal vesicle duct
• Primary hormones that help the female reproductive system function

  • Progesterone
• Seminal vesicle


  Accessory gland that contributes most of the fluid in semen
• Progesterone


  Creates a healthy uterine lining to support a fertilized egg, embryo and fetus
• Prostate gland


  Accessory gland that secretes alkaline fluid to help sperm swim
• Ovulation


  1. A mature egg is released from the ovaries and travels down the fallopian tube

  2. The egg survives for 12-24 hours, then it disintegrates into the uterine lining and eventually sheds with the monthly period
• Bulbourethral gland


  Accessory gland that lubricates the urethra
• Menstrual cycle


  Normal vaginal bleeding that occurs as part of a woman's monthly cycle