Meiosis I II Making Sperm and Eggs Learning

Meiosis I & II Making Sperm and Eggs

Learning Objectives • Describe how the process of meiosis results in haploid cells • Summarize the events of meiosis

Goal #1 of Meiosis Reduce genetic material by ½ in gametes. Without Meiosis: Sperm Egg Offspring too much! With Meiosis: Sperm Egg Offspring Just right!

Goal #2 of Meiosis Increase genetic variation in offspring Without Meiosis: With Meiosis:

2 Phases of Meiosis I - Homologous chromosomes separate Meiosis II - Sister chromatids separate

Meiosis I - Prophase I • Homologous chromosomes pair and condense • Crossing over occurs

Crossing Over Homologous chromosomes overlap. Crossing over increases genetic variation.

Meiosis I - Metaphase I • Chromosome pairs align along the equator of the cell.

Meiosis I - Anaphase I Chromosomes separate and move to opposite poles.

Meiosis I - Telophase I • Nuclear envelope reassembles • Cytokinesis divides cell into two

End of Meiosis I At the end of meiosis I, two diploid cells are produced.

Meiosis II - Prophase II • Nuclear envelope breaks down • Spindles form

Meiosis II - Metaphase II • Chromosomes align along equator of cell

Meiosis II - Anaphase II • Sister chromatids separate and move to opposite poles.

Meiosis II - Telophase II • Nuclear envelope reassembles • Cytokinesis divides the cell

End of Meiosis II • 4 haploid cells • One copy of each chromosome

Result of Meiosis Polar Bodies Females: One egg and three polar bodies Males: Four sperm cells

You. Tube Video Meiosis

You. Tube Video Crossing Over Animation Crossing Over Song and Dance

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Types of Body Cells Somatic cells – all cells except gametes Gametes– sex cells: sperm and egg cells

Meiosis I - Anaphase I • Chromosomes separate and move to opposite poles. • Sister chromatids remain attached at their centromeres.