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.
- 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.
THE HUMAN REPRODUCTIVE SYSTEM
- Reproductive system functions in gamete
- Fusion of male and female gametes to form a zygote
THE MALE REPRODUCTIVE SYSTEM
- Seminal vesicles
- Prostate gland
- Bulbourethral glands
- Scrotal sac encloses testes
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
THE FEMALE REPRODUCTIVE SYSTEM
- Uterine tubes
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
- Degeneration of the endometrium
- 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
The BIRTHING PROCESS
- Uterine contractions begin
- Contraction continues until cervix dilates to 10 cm.
- Uterus pushes baby through vaginal canal
- Placenta delivered after baby comes out.
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