Asexual vs Sexual Reproduction

• Reproduction is how organisms create new organisms
• There are two methods of reproduction: Asexual and sexual

Asexual Reproduction

• Requires a single parent
• Results in offspring genetically identical to the parent (clones)
• Examples include binary fission, budding, spore formation, fragmentation, regeneration, and parthenogenesis
• Advantages include not needing a mate and a high chance of offspring survival in stable environments
• A disadvantage is the lack of genetic diversity, which can be deadly if the environment changes

Sexual Reproduction

• Requires two parents
• Requires the joining of gametes (sperm and egg) to form a zygote
• Examples include insects, plants, animals, mammals, and fish
• Results in offspring that are genetically similar but not identical to the parents
• An advantage is the greater genetic variation of the offspring, increasing their chances of survival in changing environments
• A disadvantage is the energy expended in finding a mate
• Sexual reproduction provides more chances for organisms to live as the planet changes because mixing genes produces different offspring, some of which may be ideal for the new conditions
• Variation lets the community develop and adapt

Chromosomes

• Thread-like structures are located in the nucleus of animal and plant cells that are made of DNA tightly coiled around proteins called histones

Sex Chromosomes

• XX chromosomes determine female sex in many species
• XY chromosomes determine male sex in many species

Genes

• Homozygous: Having two identical alleles for a particular gene
• Heterozygous: Having two different alleles for a particular gene

Mitosis

• A type of cell division that results in two daughter cells, each having the same number and kind of chromosomes as the parent
• Typical of ordinary tissue growth

Meiosis

• A type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell
• Involved in the production of gametes and plant spores

DNA Structure

• DNA carries genetic information
• It's composed of four bases (Adenine, Thymine, Cytosine, and Guanine) arranged in a double helix structure

Stages of Cell Division

• Prophase: The cell gets ready by condensing its DNA
• Prometaphase: The DNA is ready, and the cell starts organizing to separate it
• Metaphase: The DNA lines up in the middle of the cell
• Anaphase: The DNA is pulled apart to opposite sides
• Telophase: The cell finishes dividing the DNA and starts to split in two

Mitosis (details)

• Occurs in body (somatic) cells throughout the body, wherever cells need to be replaced or where growth is occurring
• Produces 2 daughter cells
• Daughter cells are genetically identical
• Involved in growth and repair

Meiosis (details)

• Occurs in sex (gametes) cells, taking place in the reproductive organs (gonads): testes in males and ovaries in females
• Produces 4 daughter cells
• Daughter cells are genetically different
• Involved in sexual reproduction, where key processes include chromosome replication and separation

Mitosis vs. Meiosis

• Mitosis produces two genetically identical daughter cells, which are necessary for growth, repair, and replacement, by replicating and dividing chromosomes once
• Meiosis produces four genetically different gametes (sex cells) by two stages of division, reducing the number of chromosomes and introducing variety through crossing over

Key Vocabulary

• Somatic: Body cells
• Diploid: Cell with a full set of chromosomes
• Equator: The middle of a dividing cell
• Poles: Opposite ends of a dividing cell
• Gametes: Sex cells (e.g., eggs and sperm)
• Gonads: Sex organs (e.g., ovary and testis)
• Haploid: Cell with half the number of chromosomes
• Mitosis: Cell division that makes body cells
• Meiosis: Cell division that makes sex cells
• Crossing over: Process in meiosis that produces genetic variation