module 9 bio

Asexual reproduction

Reproduction involving one parent, producing genetically identical offspring through mitosis.

Sexual Reproduction

Reproduction involving two parents, each contributing half their DNA, producing genetically diverse offspring through meiosis + fertilization.

Diploid (2n)

A cell with two sets of chromosomes; humans have 46. Found in body cells.

Haploid (n)

A cell with one set of chromosomes; humans have 23. Found in gametes (egg & sperm).

Mitosis

Cell division that produces two identical diploid cells; used for growth, repair, and asexual reproduction.

Meiosis

Cell division that produces four genetically different haploid gametes for sexual reproduction.

Prophase I

Tetrads form and crossing over occurs between homologous chromosomes.

Metaphase I

Tetrads line up randomly along the metaphase plate, allowing independent assortment.

Anaphase I

Homologous chromosomes separate and move to opposite poles.

Telophase I + Cytokinesis

Cell divides into two haploid cells, each with duplicated chromosomes.

Prophase II

Spindle fibers form in each haploid cell; chromosomes begin moving.

Metaphase II

Chromosomes line up single-file at the metaphase plate.

Anaphase II

Sister chromatids separate and move to opposite poles.

Telophase II + Cytokinesis

Cells divide again to form four genetically distinct haploid gametes.

Independent Assortment

Random alignment of homologous chromosome pairs during Metaphase I & II, producing unique combinations of chromosomes in gametes.

Crossing Over

Exchange of DNA between non-sister chromatids in a tetrad during Prophase I, creating recombinant chromosomes.

Fertilization

Fusion of two haploid gametes to form a diploid zygote; increases diversity because gametes are genetically different.

Benefit of Genetic Diversity

Increases chances of survival and adaptation and lowers the chance of inheriting two recessive genetic disease alleles.1

Role of Mitosis in Humans

Produces identical diploid cells for growth, tissue repair, and development after fertilization.

Role of Meiosis in Humans

Produces haploid gametes (egg and sperm) and increases genetic variation for sexual reproduction.