Reproduction Notes

Reproduction—ability to pass genetics on and make the next generation

            *one basic, defining characteristic of life

2 methods of reproduction:

  • Asexual Reproduction—process of forming a new individual from a single parent
    1. Offspring have no genetic variation and are 100% identical to parent

 

  • Sexual Reproduction—process of forming a new individual from 2 parents
    1. Offspring have new combinations of parents’ genes
    2. Receive 50% of genetics from each parent
      1. Number of combinations is limitless
      2. Offspring is different from both parents

 

Asexual Reproduction

--most common in plants; also occurs in bacteria (single celled), fungi, etc.

Pro: reproduction is very quick and only requires one organism

Con: do not receive a mix of traits; gets all good, but also all bad, that parent had

            --offspring is an exact genetic copy of the parent

            Examples:

  • Vegetative Propagation: new plant grows from part of parent plant, or special plant structure (like bulbs)
    1. Potato—eyes grow stems that grow into new plants
    2. Strawberry—sends out runners (long stems) that grow new plants along them

  • Binary fission: Bacteria reproduces by growing and dividing in half
    1. DNA copies itself and the cell grows
    2. Cell divides into 2 cells as new membranes form to split cell
    3. One copy of the DNA is contained in each cell
  • Fragmentation: invertebrates (like flatworms) divides into two; each half regenerates into a new flatworm
  • Parthenogenesis: (some insects, fish, lizards) unfertilized egg cell grows into a new organism
    1. Common in honeybees—fertilized eggs become workers, unfertilized eggs become drones

 

Sexual Reproduction

--combines genetic information from 2 parents (one male, one female)

Pro: creates more genetic diversity

            --may receive diseases from parent, but may not if other parent doesn’t have them

Con: reproduction is a slower, more complex process

            *Males produce specialized reproduction cells called sperm

            *Females produce specialized reproduction cells called eggs

                                 (Ostrich egg is the largest cell in the world)

            *Sperm cells and egg cells combine in process called fertilization

                        --combination creates a zygote—the first cell of a new organism

            --Sperm cells and egg cells each only contain ½ of an organisms DNA, zygote ends up with complete DNA sequence

            --human sperm and eggs each only have 23 chromosomes, so zygote ends up with complete set of 46 chromosomes, mixing the DNA of the parents

 

--In flowering plants: flower contains reproductive cells (sperm in pollen, egg in ovary deep in flower)—need pollinators (bees, etc) to transfer pollen between flowers to reproduce

            --fertilized egg grows into embryo in seed, and can grow into plant when planted

*Many species can reproduce both sexually and asexually:

            Aspen trees, starfish, sponges, some other plants and fungi