Presentation on theme: "Sexual Division of Cells"— Presentation transcript:
1Sexual Division of Cells MeiosisSexual Division of Cells
2Gamete vs. Zygote What is a Gamete? Egg & Sperm What is a Zygote? When two gametes come together (fertilization)
3Why your body can not use mitosis to make sperm or eggs? A typical cell in your body has 46 chromosomes (23 pairs of homologous chromosomes). Suppose that human sperm and eggs were produced by mitosis. How many chromosomes would each sperm or egg have?46
4Why your body can not use mitosis to make sperm or eggs? If a sperm of this type fertilized an egg of this type, and both the sperm and egg contributed all of their chromosomes to a zygote, how many chromosomes would the resulting zygote have?92
5Why your body can not use mitosis to make sperm or eggs? In humans, how many chromosomes should a zygote have, so the baby’s body cells will each have a normal set of chromosomes?46
6Why your body can not use mitosis to make sperm or eggs? Obviously, if the body used mitosis to make sperm and eggs, the resultant zygote would have too many chromosomes to produce a normal baby. TO produce a normal zygote, how many chromosomes should each sperm and egg have?23
7Gamete vs. Zygote What is a Gamete? Egg & Sperm What is a Zygote? When two gametes come together (fertilization)
8To produce the needed number of chromosomes in the sperm and eggs… Meiosis reduces the number of chromosomes by half.A gamete (eggs and sperm) has half the number of chromosomes as a normal cell.During fertilization the sperm and egg unite to form a single cell called the zygote.The zygote contains 23 chromosomes from the sperm and 23 chromosomes from the egg.A zygote has 46 chromosomes .A zygote undergoes mitosis to begin to form an embryo and continue to grow and develop.
9Diploid and Haploid Cells 4623ReproductionHaploid cells do not have all the DNA and therefore can not function like somatic cells
10Gamete vs. ZygoteWhat is a Gamete?HaploidWhat is a ZygoteDiploid
11Review! Discuss with your partner - Why do we need Meiosis to occur? What is the difference between a Gamete and a zygote?What is the difference between haploid and diploid?
12Where do your genes come from? MeiosisWhere do your genes come from?
13Homologous Chromosomes Chromosomes are lined up from biggest to smallest (except the last pair). Each pair contains one pink (maternal) and blue (paternal) chromosome. The pairs are homologous.X and Y are the sex chromosomes – they determine the sex of the individual
14Homologous Chromosomes 9. Each pair is homologous – meaning it is the same size, shape and carries the same genes.Homologous Chromosomes –Chromosomes that are the same size, shape and carry the same genes
1611. What are the two types of division shown? Mitosis and meiosis 12. Which type of division producesDiploid cells? MitosisHaploid cells? (egg and sperm) meiosis13. Which type of cell division, mitosis or meiosis, do you think is normally used to produce new cells for:Growing from a baby to an adult mitosisHealing a wound? mitosis13. Making egg and sperm? meiosis
17Review! Discuss with partner what we just spoke about What is the differences between Haploid and Diploid?What is a homologous pair?What are the differences between mitosis and meiosis that you know so far?
18Cell Division with Meiosis Where do your genes come from?
19The cell cycle remains the same except… G1Division: meiosis & cytokinesisSG2
20VIDEO Meiosis makes unique haploid cells. As you study meiosis focus on two things:How are we ‘mixing things up’ so that our offspring are unique?How are we moving and separating the chromosomes so that we end up with ½ the material?INTRO: Difference between meiosis and mitosis
21Prophase IProphase I is the longest and most complex phase.All of the events that occurred during prophase of mitosis occur +Homologous chromosomes come together to form a SYNAPSE (TETRAD).CROSSING-OVER occurs.
23Metaphase IHomologous chromosomes line up randomly at the center of the cell. We call this independent assortment.
24Anaphase IDuring anaphase the homologous chromosomes in the center of the cell divide.
25Telophase I / Cytokinesis Telophase I two nuclei form and cytokinesis occurs resulting in 2 haploid daughter cells.
26REVIEW! Do you understand how a haploid cell is created? Discuss with partner – what happens in Meiosis 1?
27Meiosis IIMeiosis II usually comes directly after cytokinesis. No growth (interphase) takes place.Meiosis II is broken into 4 events:prophase IImetaphase IIanaphase IItelophase II.The steps of Meiosis II are identical to mitosis.
28Prophase IIProphase II is the same as prophase in mitosis.
29Metaphase IIMetaphase II is the same as metaphase in mitosis.
30Anaphase IIAnaphase II is the same as anaphase in mitosis. Notice that the sister chromatids separate.
31Telophase IITelophase II is the same as telophase in mitosis.
32VIDEO Remember meiosis makes unique haploid cells. As you watch the video again pay attention to:How are we ‘mixing things up’ so that our offspring are unique?How are we moving and separating the chromosomes so that we end up with ½ the material?
33Review!Discuss with your partner –What happens in Meiosis II?
34What is the goal of meiosis? Goals – reduce the chromosome number & mix up the DNAMeiosis 2Goals – separate sister chromatids and form 4 cells
35What 2 important things are accomplished through meiosis 1? reduce the chromosome number & mix up the DNA
36What 2 important processes help mix up the DNA in meiosis 1? Crossing over (during prophase I)Independent Assortment (during Metaphase I)
37What is major difference between metaphase 1 and 2? Metaphase I – homologous pairs line upMetaphase II – individual chromosomes line up
38What is the major difference between anaphase 1 and 2? Anaphase I – homologous chromosomes separateAnaphase II – sister chromatids separate
39Introduction to Meiosis Review Sheet What are the major differences between diploid and haploid cells?How similar are homologous chromosomes?How similar are sister chromatids?Cell 1 = Cell 2 = Cell 3 = Cell = 4Arrow A = Arrow C =Would you expect the genetic information in Cell 4 to be identical to chromosome content of Cell 1? Explain.
40Do you know meiosis?Why is meiosis necessary for sexually reproducing organisms?Needs to reduce number of chromosomes in order to have an offspring with the correct amount of DNAGenetic recombination – DNA is “mixed up”Are sister chromatids identical?YES!Are homologous chromosomes identical?Not identical. They are similar.One comes from female and one comes from male.They are the same shape, size and carry the same genes
41Do you know meiosis?In Prophase I, how many homologous chromosome pairs are present?23What is crossing over? When does it occur and why is it important?It is when homologous chromosomes swap genes during prophase IGenetic recombination – it creates genetically unique offspringHow can you tell by looking at a cell whether it is in metaphase I or II?Metaphase I – homologous chromosomes line up – double lineMetaphase II - sister chromatids line up – one line
42Do you know meiosis?What is independent assortment? When does it occur and why is it important?Homologous chromosomes randomly line up during Metaphase I.Genetically unique offspringHow can you tell by looking at the cell whether it is in anaphase I or II?Anaphase I – homologous chromosomes are separatedAnaphase II – sister chromatids are separated
43Required Reading #3 What are homologous chromosomes? Each chromosome that come from the male parent has a corresponding chromosomes from the female parent.What is the difference between a haploid cell (gamete) and diploid cell (somatic)?DIPLOID = “two sets” (2N) – cell contains both sets of homologous chromosomesHAPLOID = “one set” (N) – cell has single set of chromosomesWhat is meiosis?Process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.What are the steps of meiosis?Meiosis 1, Meiosis 2
44Required Reading #3 What is a tetrad? Pairing of the homologous chromosomes during Meiosis 1What is crossing over? Why is it important?When tetrads exchange portions of their chromatidsLook at figure How is meiosis different in men and women?Male = produce 4 gametes (sperm)Female = only one gamete (out of 4) is actually involved in reproductionBECAUSE the division at the end of meiosis 2 is uneven so that a single cell receives most of the cytoplasm – known as eggRemaining 3 are known as polar bodies and usually do not participate in reproduction.Compare and contrast mitosis and meiosis.Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces 4 genetically different haploid cells.