Meiosis Unit Flashcards

Key Terms and Definitions

• Homologous: Sets of chromosomes where each chromosome from one parent corresponds to one from the other parent.
• Diploid: Cells containing two sets of homologous chromosomes; also referred to as body cells or somatic cells.
• Haploid: Cells with one set of chromosomes, known as sex cells or gametes.
• Meiosis: Cell division process reducing the chromosome number by half, producing haploid cells from diploid cells.
• Zygote: The fertilized egg resulting from the fusion of sperm and egg cells.

Meiosis Process

• Begins with a diploid cell and results in four haploid cells.
• Consists of two rounds of division: Meiosis I and Meiosis II, separating homologous chromosomes and then sister chromatids.

Key Stages of Meiosis

• Prophase I: Homologous chromosomes pair up, forming tetrads; crossing over occurs.
• Metaphase I: Homologous pairs line up at the cell equator, spindle fibers attach to centromeres.
• Anaphase I: Spindle fibers pull homologous chromosomes to opposite poles of the cell.
• Telophase I/Cytokinesis: Nuclear membranes form around each cluster of chromosomes; two new cells are created.
• Prophase II: Chromosomes become visible again; centrioles replicate.
• Metaphase II: Sister chromatids align along the equator; centromeres attach to spindle fibers.
• Anaphase II: Sister chromatids are pulled apart to opposite poles.
• Telophase II: Nuclear membranes reform, resulting in the division of the cytoplasm and yielding four haploid daughter cells.

Genetic Outcomes and Comparisons

• Meiosis increases genetic variation through processes like crossing over.
• Mitosis produces two genetically identical diploid cells; meiosis produces four genetically different haploid cells.
• Male meiosis results in four usable sperm cells, while female meiosis typically results in one usable egg cell due to unequal cytokinesis.

Differences Between Mitosis and Meiosis

• Meiosis occurs in sex cells for reproduction while mitosis occurs in body cells for growth and repair.
• Meiosis includes two divisions and results in haploid cells, while mitosis results in diploid cells.

Tetrads and Crossing Over

• Tetrads consist of two homologous chromosomes, each with two sister chromatids, forming during prophase I.
• Crossing over occurs during prophase I, contributing to genetic diversity by exchanging segments between homologous chromosomes.

Additional Facts

• Diploid chromosome number is represented as 2N, while haploid as N.
• Meiosis occurs in reproductive organs, necessary for gamete formation.
• The difference in meiotic processes between males and females is driven by reproductive strategies: males produce continuously, whereas females have a finite number of eggs.