Chapter 11-4 Meiosis

Meiosis Vocabulary Diploid Haploid Gametes Homologous chromosomes Crossing over Tetrad

So lets talk about making a person So who do you look like? What holds the genetic information? How is this genetic information passed to the next child? How many sets of chromosomes do you have? What are homologous chromosomes? Where do you get your sets of chromosomes?

Meiosis Most cells have two sets of chromosomes This is called diploid (2 sets of 23) 2n = diploid #, humans 2n = 46 Gametes have one set of chromosomes This is called haploid cell (1 set of 23) n = haploid #, humans n = 23 Sperm, egg, pollen are examples Meiosis is the process of making haploid cells from diploid cells Haploid + haploid = diploid /fertilization

Meiosis Meiosis has two divisions Meiosis 1 Meiosis 2 First division separates the homologous chromosomes Crossing over of genetic material can take place Meiosis 2 2nd division separates the sister chromatids into individual chromosomes Process is like mitosis Except for the number of chromosomes Each division has same 4 ‘steps’ Prophase, metaphase, anaphase, telophase

Figure 11-15 Meiosis Meiosis I Interphase I Section 11-4 Prophase I Metaphase I Anaphase I Cells undergo a round of DNA replication, forming duplicate Chromosomes. Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. Spindle fibers attach to the chromosomes. The fibers pull the homologous chromosomes toward the opposite ends of the cell. Go to Section:

Figure 11-17 Meiosis II Meiosis II Section 11-4 Prophase II Metaphase II Anaphase II Telophase II Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original. The chromosomes line up in a similar way to the metaphase stage of mitosis. The sister chromatids separate and move toward opposite ends of the cell. Meiosis II results in four haploid (N) daughter cells. Go to Section:

Mitosis vs Meiosis Mitosis Meiosis 1 division 2 daughter cells Exact copies of parent cells Diploid to diploid Purpose Growth Repair Asexual reproduction Meiosis 2 divisions 1st separates pairs 4 daughter cells Each unique Diploid to haploid Purpose Make gametes/ sex cells Leads to genetic variation due to crossing over