Mitosis is used for cell division throughout the body, producing genetically identical daughter cells.
Meiosis is specialized for the production of gametes (sperm and eggs), reducing chromosome number by half to create haploid cells, ensuring genetic diversity.
Fertilization combines haploid gametes to form a diploid zygote.
Phases of Meiosis
Meiosis Overview
Meiosis involves two sequential rounds of cell division: Meiosis I and Meiosis II.
Meiosis I: Homologous chromosomes (paired chromosomes from each parent) are separated.
Meiosis II: Sister chromatids (identical copies of a chromosome) are separated, similar to mitosis.
Meiosis I
Interphase
A preparatory phase where the cell grows, duplicates its DNA, and prepares for division.
Prophase I
Chromosomes condense and pair up with their homologous partner.
Crossing over occurs, where homologous chromosomes exchange DNA segments, facilitated by the synaptonemal complex.
Crossovers are visible as chiasmata, important for genetic variance.
Metaphase I
Homologous pairs line up at the metaphase plate.
Random orientation allows for various combinations of paternal and maternal chromosomes.
Anaphase I
Homologous chromosomes are pulled to opposite poles, sister chromatids remain joined.
Telophase I
Chromosomes reach opposite poles.
Cytokinesis occurs, forming two haploid daughter cells.
Meiosis II
Prophase II
Chromosomes condense again, and the nuclear envelope breaks down.
Metaphase II
Chromosomes align individually at the metaphase plate.
Anaphase II
Sister chromatids pulled apart to opposite poles.
Telophase II
Chromosomes decondense, nuclear envelopes form.
Cytokinesis results in four genetically diverse haploid cells.
Genetic Variation in Meiosis
Crossing over and random orientation during metaphase I lead to genetic diversity.
Human meiosis can produce over 8 million different gametes due to these mechanisms.
Special Considerations in Meiosis
During spermatogenesis, meiosis produces four functional sperm cells.
During oogenesis, typically one functional egg and polar bodies (non-functional) are produced due to cytoplasmic division.
Importance of Meiosis
Meiosis introduces genetic diversity, crucial for evolution and species survival.
The mixing of genes contributes to variations seen in offspring, important for adapting to different environments.