Stages of Meiosis Meiosis I

Interphase Same as mitosis DNA in chromatin Centrioles DNA Nuclear Membrane Same as mitosis DNA in chromatin Cells are growing and doing their normal cell jobs DNA= 2n

Prophase I DNA condenses into chromosomes and homologous chromosomes pair (homologous= carry same genes) These chromosome pairs are called tetrads Crossing over occurs in this step

Crossing Over Parts of homologous chromosomes are exchanged

Metaphase I Like metaphase in mitosis Chromosomes like up in the center of the cell Nuclear membrane now gone

Stages of Meiosis Meiosis II

Prophase II The two newly formed cells continue into the next cycle of divisions known as Meiosis II. No DNA replication between meiosis I and II Centrioles and spindle fibers appear as the nuclear membrane breaks down and disappears.

Metaphase II Like all other metaphases Chromosomes like up in the center of the cell Nuclear membrane now gone

Anaphase II Same as anaphase in mitosis Centromeres detach from each other Chromatids are pulled to opposite ends of the cells by microtubules

Telophase II and Cytokinesis Nuclear membrane reforms Cytoplasm is divided between new cells DNA goes back to chromatin

Human Males vs. Females In human males, all four cells become viable haploid gametes In females, only one of the cells will develop into a egg, rest are polar bodies

Sibling Variation Using your understanding of meiosis, explain why brothers and sisters from the same parents have similarities and differences in appearance. The variety of genetic inheritance due to crossing over and random gene selection in meiosis can account for differences and similarities between siblings.