Be able to define meiosis.
• Know and be able to explain, recognize and/or draw each phase of meiosis I & II.
• Be able to explain the importance of meiosis.
• Be able to explain the consequences of chromosome segregation and sex
chromosomes in meiosis.
• Be able to explain and/or draw the mechanisms that generate genetic variability
Meiosis is a type of cell division that occurs in sexually reproducing organisms to produce gametes (sperm and egg cells). It involves two rounds of cell division, resulting in four daughter cells with half the number of chromosomes as the parent cell.
Meiosis I:
1. Prophase I: Chromosomes condense and pair up with their homologous partners to form tetrads. Crossing over occurs, where sections of chromosomes are exchanged between homologous pairs.
2. Metaphase I: Tetrads line up at the metaphase plate.
3. Anaphase I: Homologous chromosomes separate and move to opposite poles of the cell.
4. Telophase I: Chromosomes decondense and the cell undergoes cytokinesis, resulting in two haploid daughter cells.
Meiosis II:
1. Prophase II: Chromosomes condense again and the nuclear envelope breaks down.
2. Metaphase II: Chromosomes line up at the metaphase plate.
3. Anaphase II: Sister chromatids separate and move to opposite poles of the cell.
4. Telophase II: Chromosomes decondense, nuclear envelopes form around each set of chromosomes, and the cell undergoes cytokinesis, resulting in four haploid daughter cells.
Importance of Meiosis:
- Produces genetically diverse offspring through crossing over and random assortment of chromosomes.
- Maintains the correct number of chromosomes in a species by reducing chromosome number in gametes.
- Allows for genetic recombination and evolution.
Consequences of Chromosome Segregation and Sex Chromosomes in Meiosis:
- Chromosome segregation ensures that each daughter cell receives a complete set of chromosomes.
- Sex chromosomes determine the sex of the offspring and play a role in genetic inheritance.
Mechanisms Generating Genetic Variability:
- Independent assortment: Homologous chromosomes line up randomly during meiosis, leading to different combinations of maternal and paternal chromosomes in gametes.
- Crossing over: Exchange of genetic material between homologous chromosomes leads to new combinations of genes on the chromosomes.
- Random fertilization: When gametes combine during fertilization, the combination of genes from two parents creates even greater genetic diversity.