Overview
This lecture explains how human males produce gametes (sperm) through the process of meiosis, highlighting chromosome behavior and key steps.
Chromosomes and Cell Types
- Human cells are typically diploid, containing two sets of chromosomes—one from each parent.
- Homologous chromosomes are matching pairs, with one maternal and one paternal chromosome.
DNA Replication and Structure
- During interphase, chromosomes are duplicated, forming sister chromatids (identical copies).
- Sister chromatids consist of DNA wound around histone proteins and further coil into helical fibers.
Steps of Meiosis
- Meiosis starts with spindle formation and centrosome migration to opposite cell poles.
- Chromosomes condense and homologous chromosomes pair up, enabling genetic recombination (swapping between nonsister chromatids).
- Microtubules from opposite poles attach to homologous chromosomes, preparing for separation.
Meiosis I
- Homologous chromosome pairs align in the cell's center at metaphase I.
- Homologous chromosomes separate to opposite poles, but each chromosome still has two sister chromatids.
- At the end of meiosis I, each daughter cell has 23 chromosomes (half the original number).
Meiosis II
- Microtubules attach again, and chromosomes align at the center.
- Sister chromatids separate and move to opposite poles.
- Nuclear envelopes reform, and each cell divides, producing four haploid cells.
Formation of Gametes
- The process starts with one diploid cell and results in four haploid cells.
- These haploid cells mature into gametes (sperm), each with a single set of chromosomes.
Key Terms & Definitions
- Diploid — a cell with two sets of chromosomes (one from each parent).
- Haploid — a cell with a single set of chromosomes.
- Homologous chromosomes — a matching pair of maternal and paternal chromosomes.
- Sister chromatids — identical copies of a duplicated chromosome.
- Meiosis — cell division process creating haploid gametes from diploid cells.
- Genetic recombination — exchange of genetic material between nonsister chromatids, increasing genetic variation.
Action Items / Next Steps
- Review the stages of meiosis and the differences between meiosis I and meiosis II.
- Be able to define key terms related to meiosis and chromosome structure.