2 One parent cell produces four daughter cells. MeiosisMeiosis is the type of cell division by which germ cells (eggs and sperm) are produced.One parent cell produces four daughter cells.Daughter cells have half the number of chromosomes found in the parent cell
3 There are 2 parts to Meiosis: During meiosis, DNA replicates once, but the nucleus divides twice.There are 2 parts to Meiosis:Meiosis 1Meiosis 2The 4 new daughter cells have variation of the parent DNA; this is genetic variation
4 Meiosis TerminologyKaryotype: Arranging of chromosomes from largest to smallest; pairing up the homologous chromosomesAutosomes: All non-sex chromosomes; (#1-22 for humans)Sex Chromosomes: Chromosomes that determine the sex of an organism (#23 for humans)Set (n): # of different chromosomes. REMEMBER: Haploid = 1set, Diploid= 2 sets
6 Karyotype of a human Is this person male or female? How many sex chromosomes are present?How many autosome chromosomes are present?How many homologous pairs of chromosomes are present?
7 Background on Meiosis Meiosis involves 2 divisions of the nucleus Meiosis STARTS with HOMOLOGOUS CHROMOSOMESHomologous Chromosomes: They are similar in shape, size & genetic content
8 Meiosis 1: 1st Division of Meiosis Prophase I: Chromosomes condense, nuclear envelope breaks, homologous chromosomes pair at ends.***Cross-Over: Part of chromatid on 1 homologous chromosome exchanges with the other chromosome***This isGenetic variationDRAW ME
9 Meiosis 1: 1st Division of Meiosis Metaphase I: Homologous chromosomes move to center of the cell by the spindle fibers.Anaphase I: Homologous chromosomes separate and move to opposite poles, BUT sister chromatids stay together. A set of chromosomes moves to each poleTelophase I: The spindle fibers disappear, cells begin to cleave; still, two sets of chromosomes are at opposite poles
11 End of Meiosis IOnce Meiosis I is complete, cytokinesis occurs and the cell splits into 2 haploid cells. These 2 cells enter Meiosis II
12 Meiosis I: STOP & THINK1. What is the purpose of Meiosis? 2. Describe genetic variation 3. Explain purpose of karyotyping 4. Explain cross-over 5. What major event occurs in Anaphase I ? 6. Are the daughter cells haploid or diploid? Explain
15 Meiosis IIProphase II: A new spindle forms around the chromosomes (no longer HOMOLOGOUS CHROMOSOMES)Metaphase II: Chromosomes line up at center & spindle fibers attach to centromereAnaphase II: Centromeres split, chromatids move to opposite poles of cellTelophase II: Nuclear envelope forms around each set of chromosomes & spindles retracts, cell begins cytokinesis
16 Result of Meiosis II 4 HAPLOID cells form as a result of Meiosis II Haploid = cell containing 1 set of chromosomes
22 Meiosis Booklet 1. Everyone needs 3 sheets of blank paper 2 Meiosis Booklet 1. Everyone needs 3 sheets of blank paper 2. Fold each one hotdog style 3. Cut straight up the fold (You should have 6 long sheets, only use 5) 4. Label each square with the phases of meiosis the same as the mitosis booklet
23 Meiosis Review Questions What type of cells are used in Meiosis? Give examples of these cells.2. Meiosis is used in sexual reproduction. Explain the process of “cross-over”3. Draw homologous chromosomes going through cross-over.4.Meiosis is divided into two parts, why?5. Define “Haploid”6. Compare and Contrast Meiosis to Mitosis.In your notebook!