BIOL1030 Animal Reproduction Topic 6

Sexual Reproduction

• typical

• Female + male gametes produced (via meiosis) fuse to form offspring

• Female + male gametes produced (via meiosis) fuse to form offspring

• Offspring vary genetically

Asexual Reproduction

• atypical

• Offspring arise from one parent

• (female) - makes copies of itself (via mitosis) - gametes optional

• One parent provides all of the offspring's DNA (alleles)

• Offspring genetically identical

Haploid

one set of chromosomes (n)

Diploid

two sets of chromosomes (2n)

Meiosis

cell division -where the number of chromosome sets are halved(2n to n)

Mitosis

cell division -where the number of chromosome sets remain the same

Methods of Asexual Reproduction

• Budding

• Fission

• Parthenogenesis

Budding

• outgrowths enlarge and separate from parent (males or females) - e.g. hydra

Fission (Fragmentation)

parent separates into two or more similar-sized or smaller individuals(males or females) - e.g. anenome

Parthenogenesis

• unfertilized eggs develop into an individual (females only)

Parthenogenesis of bees and wasps

• Queen produces haploid eggs (via meiosis)

• Mates and stores sperm

• Lays 2 egg types: Fertilized (diploid) → Females

  • Fertile queens, sterile workers

• *Unfertilized (haploid) → Males

  • Fertile haploid drones

Parthenogenesis of Invertebrates

• e.g. Daphnia- Female produces diploid eggs (mitosis) Unfertilized eggs → parent clones

Parthenogenesis of Vertebrates

e.g. whiptail lizard

• Only females (no males)

• Female produces diploid eggs

• (modified form of meiosis, involving DNA doubling and then halving)

Dioecious ('two houses') species

= male OR female sexual parts on different individuals

-Difficult to find mates → adaptations...

Monoecious ('one house') species

male AND female sexual parts on same individual - Hermaphrodite

Simultaneous

male & female parts at same time

Cross-fertilize

• mate with others

• offspring genetically distinct from parent

Self-fertilize

• mate with self

• • Cost - offspring are genetically identical

• Benefit - reproduce even if hard finding mates

Monoecious

• Simultaneous

• Sequential

• Protandry or Protogyny

Sequential ('sex reversal')

• start life as one sex and develop into the other

Protandry (common)

= male to female

e.g. clown fish

• born males

• • largest → female; 2nd largest is male partner

  • female dies, largest male → female

Protogyny (rare)

= female to male (other fish species)

Multiple sex reversals (rare)

e.g. Whiptail lizard - all female but behave like females & males

• Ovulation triggered by hormone changes & behaviour (copulation)

• Female-like - when about to ovulate (high estradiol)

• Male-like - just after ovulation (high progesterone)

Gametogenesis

formation of gametes

Spermatogenesis

Primordial Germ Cell (diploid) - divides by mitosis - produces 2 daughter cells:

1. Spermatogonial stem cell (regenerated → unlimited sperm)

2. Spermatogonium (diploid)

   • Mitosis → Primary Spermatocyte

   • Meiosis I (2 cells-equal sizes)

   • Meiosis II (4 cells-equal sizes)
     form Spermatids
     - mature → Sperm cells
     (gametes)
     • All 4 cell products of meiosis become
     sperm
     • Starts at puberty (whole process takes
     3-4 weeks)

Oogenesis

Primordial Germ Cell (diploid) - divides
by mitosis - produces 2 daughter cells:
- Oogonium (no regenerating germ
cells → limited eggs)
- Mitosis → Primary Oocyte
- Meiosis I (2 cells-unequal size) form
haploid Secondary Oocyte
- Small - polar body (excess DNA) & Large
- Meiosis II (2 cells-unequal size) form
haploid Ootid
- Small - polar body (excess DNA)
-Large → Ootid → Fertilized Egg
• 1 cell product of meiosis becomes an
egg (large, lots of food/yolk to nourish
embryo)
• Starts pre-birth → pauses (birth) →
resumes (puberty) → ends (menopause)

Reproductive Cycles

• Most animals exhibit reproductive cycles related to changing seasons

• Conserve resources and reproduce when sufficient energy sources or stores are available and when environmental conditions favour offspring survival

• Reproductive cycles are controlled by hormones, regulated by environmental cues (e.g., day length, seasonal temperature)

Ovulation

release of mature eggs at the midpoint of a female cycle