Presentation on theme: "ANNOUNCEMENTS LAB #3 MITOSIS & MEIOSIS has been moved to FRIDAY because I’m not finished grading lab #1. DO THE SAMPLE FREE RESPONSE QUESTIONS FOR HOMEWORK."— Presentation transcript:
1ANNOUNCEMENTSLAB #3 MITOSIS & MEIOSIS has been moved to FRIDAY because I’m not finished grading lab #1.DO THE SAMPLE FREE RESPONSE QUESTIONS FOR HOMEWORK. I’ll post them on facebook and teacherweb.Do the lab bench exercise for LAB 3 mitosis & meiosisLAB 3 is now on FRIDAY- you will have a lab quizHere are other websites that will help you:TEST #2 IS TUESDAY 10/9… YOUR BIG CHANCE TO BRING YOUR GRADE WAY UP! :)
2Meiosis & Sexual Life Cycles CHAPTER 13Meiosis & Sexual Life Cycles
4ASEXUAL REPRODUCTION reproduction which does not involve meiosis, reduction, or fertilization. Only one parent is involved in asexual reproduction.A lack of sexual reproduction is relatively rare among multicellular organisms, for reasons that are not completely understood.Current hypotheses suggest that asexualreproduction may have short term benefitswhen rapid population growth isimportant or in stable environments,while sexual reproduction offers a netadvantage by allowing more rapidgeneration of genetic diversity, allowingadaptation to changing environments.Types of asexual reproduction1.1 Binary fission1.2 Budding1.3 Vegetative reproduction1.4 Spore formation1.5 Fragmentation1.6 Parthenogenesis1.7 Agamogenesis
5Figure 13.x1 SEM of sea urchin sperm fertilizing egg Sexual reproduction= genetic recombination= diversity= better chance of survivalSexual reproduction offersa net advantage by allowingmore rapid generation ofgenetic diversity, allowingadaptation to changingenvironments.
6WHY SEX?Natural selection operates on populations through the phenotypic differences (traits) that individuals display; meiosis followed by fertilization provides a spectrum of possible phenotypes on which natural selection acts, and variation contributes to the long-term continuation of species.
7Figure 13.4 The human life cycle Fertilization involves the fusion of two gametes, increases genetic variation in populations by providing for new combinations of genetic information in the zygote, and restores the diploid number of chromosomes.Meiosis ensures that each gamete (sperm/egg) receives one complete haploid (1n) set of chromosomes.
8Figure 13.x3 Human female karyotype shown by bright field G-banding of chromosomes
9Figure 13.x5 Human male karyotype shown by bright field G-banding of chromosomes
10QUIZ: What determines whether you are genetically male or female? What are autosomes?What are gametes?What is a zygote?What is the difference between a diploid cell and haploid cell?What is Meiosis?Sex chromosome combo XX=female XY=male.Non-sex chromosomes (1-22)Sex cells- sperm or egg.Fertilized egg.Diploid=2n (homologous chromosomes); hapliod=1n (only one of each kind of chromosome)Nuclear division that includes a “reduction” it reduces the chromosome number by 1/2.
11The creation of gametes for sexual reproduction (MEIOSIS)Occurs in 2 stages:MEIOSIS I- REDUCTIONseparates homologous chromosomes.2n ---> 1nex > 23split up the “pairs” or TETRADLaw of Segregation- alleles of a geneSeparate during gamete formation.MEIOSIS IIseparates sister chromatids1n (2 chromatids) --->2 separate x 1n chromosomes*similar to mitosis.
12Figure 13.7 The stages of meiotic cell division: Meiosis I
13meiosis1 is like separating all the pairs of shoes in your closet… putting one of each kind in one room & the other in another room.During meiosis, homologous chromosomes are paired, with one homologue originating from the maternal parent and the other from the paternal parent. Orientation of the chromosome pairs is random with respect to the cell poles.Separation of the homologous chromosomes ensures that each gamete receives a haploid (1n) set of chromosomes composed of both maternal and paternal chromosomes.
14Figure 13.7 The stages of meiotic cell division: Meiosis II
15Major Differences between Mitosis & Meiosis: (2 divisions- not 1 creates 4 haploid cells- not 2 diploid)PROPHASE IS SPECIAL…In Prophase 1 of Meiosis 1the homologous chromosomesline up together.2. SYNAPSIS is the process ofpairing homologouschromosomes.3. TETRAD is 4 chromatids ofa homologous pair.4. CHIASMATA are the X shapedregions of chromatid overlap.5. CROSSING OVER producesrecombinant chromosomeswhen pieces break off & attach.
16During meiosis, homologous chromatids exchange genetic material via a process called “crossing over,” which increases genetic variation in the resultant gametes.Benefit to the organism’s species because it produces genetic variation.Recombinant chromosomes are produced.New combinations of your parent’s genes in your gametes.Diversity = better chances for survival of a species.CROSSING OVER
17Figure 13.7 The stages of meiotic cell division: Meiosis I
18INTERPHASE I Cell grows by producing proteins (cyclin) and organelles Chromosomes replicateCentrosomes/centrioles replicatePreparation for cell division
19PROPHASE I Chromatin condenses Homologous replicated chromosomes line up together“SYNAPSIS”Crossing over occursTETRAD consists of 4 chromatidsCHIASMA(TA)
20METAPHASE ISpindle microtubules from opposite poles attach to one each of a homologous pair of replicated chromosomes.Homologous pairs poised to move to opposite poles of the cell.Position of pairs on metaphase plate leads to variation due to independent assortment.=Alleles of different genes assort independently during gamete formation.
21Figure The results of alternative arrangements of two homologous chromosome pairs on the metaphase plate in meiosis I
22Independent Assortment means that when you separate these pairs it doesn’t matter if one side gets the left or right shoe. Each pair is split up independently.How many ways could you split up these 12 pairs?2 n (n=#chromosomes)2 12 =For humans???? =
23ANAPHASE I Homologous pairs of chromosomes are separated. Sister chromatids remain attached at their centromere.Independent assortment occurs now… the separation of each chromosome pair occurs independently.
24Figure The results of alternative arrangements of two homologous chromosome pairs on the metaphase plate in meiosis I
25TELOPHASE I Cytokinesis occurs. 2 haploid daughter cells are formed. Each chromosome still consists of 2 sister chromatids.Meiosis II is next.(INTERKINESIS)
26Figure 13.7 The stages of meiotic cell division: Meiosis II
27MEIOSIS II Essentially mitosis Begins with haploid cells (unlike mitosis which starts with diploid cells)Sister chromatids pulled apartResults in 4 haploid cells.Each with one set of chromosomes.
29SPERMATOGENESISSperm are produced in the seminiferous tubules of the testes of adult males.Each ejaculation contains million sperm cells. They live 4 days.Each diploid stem cell (spermatogonium) produces 4 haploid sperm cells (spermatozoa)
30OOGENESISDIFFERENCES BETWEEN OOGENSIS & SPERMATOGENESIS:Cytokinesis is unequal- almost all the cytoplasm is taken by a single daughter cell SECONDARY OOCYTE. This cell can go on to form the ovum (egg).The other smaller cells are Polar bodies.At birth, ovary already contains all the primary oocytes.Oogenesis has long resting periods. Starting at puberty, a single primary oocyte completes meiosis I each month. The secondary oocyte completes meiosis II only if a sperm cell enters it.* Ootid is an undifferentiated ovum.