Reproduction

An Overview

Reproduction

• Reproduction is the process by which an organism produces others of its same kind

• It is the way a species is continued

• May be either sexual or asexual depending on the species

Comparison of Asexual and Sexual Reproduction

Asexual Reproduction• One parent• Genetically identical

to parent• Cell copies or clones

itself and splits off from a parent

• Common in simple organisms such as bacteria and ferns

Sexual Reproduction• Two parents• Offspring similar to

parents, but not genetically identical

• Two gametes fuse nuclei to form a zygote

• Common in complex organisms such as vertebrates

Advantages/Disadvantages

• Asexual • Advantage:

– Numerous offspring with little effort or time used

• Disadvantage:– Only source of

diversity is mutation (a mistake in copying the DNA)

– Population is uniform

• Sexual• Advantages:

– Greater diversity in offspring

– Species can evolve

• Disadvantage:– Requires more time

and effort to reproduce

Asexual Reproduction:Genetically Identical Offspring

• Budding

• Regeneration

• Parthenogenesis

… Cloning???

Binary Fission…

• most common form of reproduction in prokaryotes and occurs in some single-celled eukaryotes

Budding…• New Organisms Arise

as an Outgrowth from the Parent Organism

• Seen Mostly in Marine Animals– Examples Include;

Hydra, Yeast, Sponges, Corals and Jellyfish…

Coral Polyp Photo courtesy Jeffrey N. Jeffords http://oceanworld.tamu.edu/students/coral/coral1.htm

Fragmentation and Regeneration…

• This refers to the ability of some animals to re-grow severed parts.

• Some of these animals can also grow new organisms from the severed pieces (Segmented Worms and Sea Stars)

Parthenogenesis…

• Offspring can arise from unfertilized eggs.

• Includes some Fish, Reptiles, Amphibians and Aphids.

• Most of these species can switch between Sexual and Asexual Reproduction.

(depending on conditions)

http://www.duke.edu/%7Ejsr6/Hawaiipics/Rhampho.jpg

http://aolsearch.aol.com/aol/imageDetails?invocationType=imageResults&query=photos+of+parthenogenic+species&img

http://spot.colorado.edu/~noyesr/TEACHING/4800%20Fall%202002.%20Biology%20and%20Evolution%20of%20Sex/Gynogenesis.Poecilia.pdf

www.ag.ndsu.nodak.edu

Examples of Sexual Reproduction

Examples of Sexual Reproduction--Pollination

Examples of Sexual Reproduction

Sexual ReproductionCellular Level

Where Is the Information for Heredity Stored?

Sexual ReproductionCellular Level

•The key to the diversity we see in organisms that reproduce sexually is the special form of cell division that takes place ONLY in the male and female reproductive organs

• Results in gametes (sex cells)that each have half of the chromosomes necessary to make an organism

•The name of this process is meiosis

•It occurs in the ovaries and testes in humans

Sexual ReproductionOrganism Level

• Fertilization- Gametes (such as egg and sperm) from two parents fuse to form a zygote (offspring)

Male and female human body cells contain 46 chromosomes in 23 pairs

Ovaries produce egg cells that each contain 23 chromosomes

Testes produce sperm cells that each contain 23 chromosomes

23

23

46

Sexual ReproductionSpecies Level

• Allows for greater genetic variability in offspring

• Allows for diversity in a population

• Allow the ability to evolve

• Why is that an important advantage for the species?