Reproduction

1
Reproduction Embryonic Development

• Ch. 27

2
Objectives Define Comprehend

• Variations and dis/advantages of sexual and
  asexual reproduction
• Fe/male reproductive anatomy
• Spermatogenesis/oogenesis
• Fertilization
• Development cleavage, gastrulation, cell death,
  induction, pattern formation
• Human development
• Childbirth

3
Sexual vs. asexual reproduction

• What is the benefit for organisms that reproduce
  sexually?
• Genetic variation
• Why is genetic variation important?
• Increases chance that some variant offspring will
  be able to survive and reproduce should sudden or
  drastic changes occur in the environment

4
Asexual Reproduction Advantages Disadvantages

• Advantages
• Dont need a mate to procreate
• Produce offspring quickly
• Perpetuation of a particular genotype
• Disadvantages
• No genetic variation!

5
Asexual reproduction Budding
6
Asexual reproduction fission
7
Asexual reproduction Fragmentation Regeneration
Linckia
8
Sexual Reproduction hermaphroditism

• Advantage for those that are either solitary or
  nonmobile

9
Sexual reproduction external fertilization

• Many aquatic invertebrates, and most fishes and
  amphibians
• Parents discharge gametes into the water where
  fertilization occurs
• Often have courtship rituals to trigger
  simultaneous gamete release

10
Sexual reproduction internal fertilization

• Sperm deposited in or close to females
  reproductive tract
• Majority of terrestrial animals
• Protects developing eggs from excessive heat and
  drying
• Requires copulation and complex reproductive
  systems

11
Human Reproduction
12
Human Reproduction
13
Meiosis Review

• Why does our body reduce our total chromosome
  number by half?
• How many cells are produced via meiosis?
• Are these cells haploid or diploid?

14
Sperm Production

• Occurs in seminiferous tubule in testis
• Multiply constantly
• 3 million cells differentiate into primary
  spermatocytes every day!

15
Egg Production

• Majority of process occurs in ovaries
• At birth, ovaries contain all follicles female
  will ever have
• Secondary oocyte released once/month
• Complete meiosis II when sperm enters

16
Fertilization
17
Sperm

• Form follows function
• Shape allows it to swim to egg
• Mitochondria provide energy necessary for sperm
  to reach its goal
• Fuel from semen
• Enzymes in acrosome
• To dissolve eggs coat

18
Fertilization
19
Fertilization

• Proteins on sperm head bind to receptor proteins
  of egg
• Ensures that sperm of other species cannot
  fertilize egg
• Fertilization envelope prevents other sperm from
  fertilizing egg
• Why?
• Too many chromosomes

20
Cleavage

• Creates a multicellular embryo from a
  single-celled zygote
• Partitions embryo into developmental regions

21
Gastrulation

• Adds more cells to embryo
• Sorts cells into distinctive layers
• Ecto, endo, and mesoderm
• Actual process varies a bit by species

22
Organ formation

• After gastrulation, cells in each of the 3 layers
  begin to differentiate into tissues and embryonic
  organs
• Notochord becomes spine
• Neural tube becomes brain and spinal cord
• Somites give rise to segmented structures
• Coelom body cavity

23
Early Organ Formation
24
Organ Formation
D\Teen Brains\Teen Brains.mpg
25
Development of Form

• Cell shape
• normal shaped cells elongate and become
  wedge-shaped
• Cell migration
• Cells crawl to specific destinations
• Join together
• Differentiate
• Programmed cell death
• Important for ex create space between fingers
  and toes

26
Induction initiates organ formation

• The effect of induction is to switch on genes
  whose expression makes the receiving cells
  differentiate into a specific tissue
• Leads to increasingly greater specialization of
  cells as organs begin to take shape

27
Pattern Formation

• Master control genes respond to chemical signals
  that tell a cell where it is relative to other
  cells in the embryo
• These signals determine which master control
  genes will be expressed
• Ultimately, which body parts will form

28
Pattern Formation

• Body part formation needs signals specifying its
  position in 3 dimensions
• Ex wing how close to main axis, to the
  anterior/posterior edge, to dorsal/ventral
  surface

29
Human Development
30
Human Development
31
Human Development

• Trophoblast secretes enzymes that enable the
  blastocyst to implant in the endometrium
• During early development, the amnion develops and
  surrounds the embryo
• protects the embryo
• The yolk sac in mammals produces the first blood
  cells and pre-cursors for gamete producing cells

32
Human Development

• HCG is secreted by placenta to maintain the
  corpus luteum of the ovary during the first 3
  mon.
• The corpus luteum secretes estrogen and
  progesterone which prevents menstruation from
  occurring
• The placenta consists of embryonic blood vessels
  and blood vessels of the endometrium
• No direct contact b/t blood of mother and embryo
• Embryo blood vessels absorb nutrients and oxygen
  from the mothers blood
• Wastes of embryo diffuse into mothers bloodstream

33
Placenta
34
Human Development

• http//media.health.discovery.com/centers/pregnanc
  y/video/video.html

35
The radical first Trimester

• Early human embryo is similar to other vertebrate
  embryos
• At about 9 weeks, embryo begins to resemble a
  human
• Now referred to as fetus
• Has all organs and major body parts
• Can determine sex by end of first trimester

36
Second trimester

• Fetus increases in size and a general refinement
  of human features occurs
• Placenta takes over task of maintaining
  progesterone secretion
• At end of 2cd trimester, fetus is active, its
  eyes are open, and teeth are forming

37
Third trimester

• Fetus grows rapidly and gains strength in
  preparation for life outside of womb
• Fetuss circulatory and respiratory systems
  undergo changes that will allow the switch to air
  breathing
• Fetus can maintain its own temperature
• Bones begin to harden and muscles thicken
• The brainstem is still controlling behavior
• Mostly reflexive

38
Childbirth

• Estrogen reaches high levels during last weeks of
  pregnancy
• Triggers formation of oxytocin receptors on
  uterus
• Oxytocin is a powerful stimulant that causes
  uterine muscles to contract
• Positive feedback
• Decreasing levels of progesterone and estrogen
  allow uterus to return to prepregnancy state
• Less progesterone in maternal blood allows
  prolactin to promote milk production in mammary
  glands