Week 9 Topic : Reproduction

Sexual VS Asexual Reproduction

Sexual reproduction – a type of reproduction in which the genetic materials from two different cells combine, producing an offspring.

  • The cells that combine are called sex cells.
    • Female – egg
    • Male – sperm
  • Fertilization – an egg cell and a sperm cell join together. A new cell is formed and is called a zygote.

Advantages of Sexual Reproduction

  • Diverse offspring – genetic variation among offspring
    • Half of the DNA comes from mom
    • Half of the DNA comes from dad
  • Due to genetic variation, individuals within a population have slight differences
    • Plants – resist diseases
    • Traits can develop to resist harsh environments that allows an organism to survive.
  • Selective Breeding
    • Used to develop many types of plants and animals that have desirable traits
    • Agriculture / farming: better plants, larger animals
    • Desirable pets

Disadvantages of Sexual Reproduction

  • Time and Energy
    • Organisms have to grow and develop until they are old enough to produce sex cells.
    • Search and find a mate
    • Searching can expose individuals to predators, diseases, or harsh environmental conditions
    • Fertilization cannot take place during pregnancy, which can last as long as 2 years for some mammals.

Asexual Reproduction

  • One parent : organism produces offspring without fertilization
  • Uniform offspring
    • Because offspring inherit all of their DNA from one parent, they are genetically identical to each other and to their parent
  • Fission – cell division in prokaryotes that forms two genetically identical cells.
    • DNA is copied
    • The cell begins to grow longer, pulling the two copies apart
    • The cell membrane pinches inward in the middle of the cell
    • Cell splits to form two new uniform, identical offspring
    • Examples: bacteria, Ecoli, pond critters
  • Budding – a new organism grows by mitosis and cell division on the body of its parent
    • The bud, or offspring is identical to the parent
    • The bud, when large enough can break off of the parent and live on its own
    • Offspring may remain attached and form a colony
    • Examples : yeast, hydra, cactus
  • Regeneration – occurs when an offspring grows from a piece of its parent
    • Producing new organisms : sea stars, sea urchins, sea cucumber, sponges and planarians
    • Producing new body parts : gecko, newts, tadpoles, crabs, hydra, and zebra fish
  • Vegetative Propagation – uniform offspring grow from a part of a parent plant
    • Parent plants send out runners
    • Where the runner touches the ground, roots can grow
    • A new plant is produced even if the runner is broken apart
    • Each new plant is uniform and identical to the parent
    • Examples: strawberries, potatoes, ivy, crabgrass

Advantages of Asexual Reproduction

  • Enables organisms to reproduce without a mate, thus no wasted time and energy
  • Enables some organisms to rapidly reproduce a large number of uniform offspring

Disadvantages of Asexual Reproduction

  • Because their offspring are identical, there is no genetic variation that can give an organism a better chance for survival
    • Example: if a weed killer can kill the parent, it will also kill the offspring
    • A whole species can be wiped out from a disease
  • Dangerous mutations in DNA – if the parent has the mutation in their DNA, the offspring will have it too.



  1. Reproductive system functions in gamete
    • Production
    • Storage
    • Nourishment
    • Transport
  1. Fertilization
    • Fusion of male and female gametes to form a zygote



Male Organs:

  • Seminal vesicles
  • Prostate gland
  • Bulbourethral glands
  • Scrotal sac encloses testes
  • Penis

 Secondary Sexual Characteristics – Male

  • Produced by testosterone
    • Deeper voice
    • Axillary and pubic hair
    • Chest and facial hair
    • Lengthen bones
    • Increased size of testes for sperm production




Female Organs:

  • Ovaries
  • Uterine tubes
  • Uterus
  • Vagina

Secondary Sexual Characteristics in Females:

  • Induced by increased LH, FSH, estrogen, and progesterone hormone levels
    • Axillary and pubic hair
    • Widen pelvis
    • Enlarge mammary tissue
    • Begin menstrual cycles

The Menstrual Cycle

  • Repeating series of changes in the endometrium
  • Continues from menarche to menopause
  • Menses
    • Degeneration of the endometrium
    • Menstruation
  • Proliferative phase
    • Restoration of the endometrium
  • Secretory phase
    • Endometrial glands enlarge and accelerate their rates of secretion


  • Occurs in upper 1/3 of Fallopian tube
  • Once one sperm enters, egg membrane changes
  • Fertilized egg = zygote


  • Implanted into thick walls of uterus
  • Chorion membranes dig into uterus to form placenta
  • Embryo supported via umbilical cord
  • Once pregnant, progesterone levels stay high in mom

First Trimester (1-3 Months)

  • Heart develops first / Neural tube develops
  • Morning sickness occurs about seventy percent of all pregnant women, and typically improves after the first trimester.
  • All body systems appear by Week 8 – Now a Fetus

 Second Trimester (4-6 Months)

  • Mostly growth / Weeks 13 to 28 of the pregnancy.
  • Looks more like a baby / fetus begins to move / quickening can be felt.
  • Some preemies survive at this stage

 Third Trimester (7-9 Months)

  • More growth / rapid growth / final weight gain takes place by the mother.
  • Kicking, rolling, stretching / Rotates head down position
  • Eyes open – Week 32 / Lungs mature



  1. Labor
    • Uterine contractions begin
    • Contraction continues until cervix dilates to 10 cm.
  1. Birth
    • Uterus pushes baby through vaginal canal
  1. Placenta delivered after baby comes out.









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