Presentation on theme: "Chapter 9 The passage of life’s organization and information from one generation to the next One way, but are there others? How do organisms pass genetic."— Presentation transcript:
1 Chapter 9The passage of life’s organization and information from one generation to the nextOne way, but are there others?How do organisms pass genetic information?Are the contributions the same from males and females?What kinds of mishaps occur and where do they originate?
2 General Life Strategies Asexual reproductioncormsfragmentationbulbsNo exchange of genetic materialOffspring are genetically identical to parentsNo time ‘wasted” finding a mateNo courtship
3 Figure 9.8 Bacterial Duplication Figure: 9.8 Caption: Quaking aspen can reproduce asexually, leading to genetically identical clones. The photograph was taken in autumn, when quaking aspen leaves turn bright yellow.
4 Some Interesting Strategies The life cycle of aphids can involve a mix of parthenogenetic (asexual) and sexual reproduction. Parthenogenetic reproduction provides the development of young from unfertilized eggs. The young are female and genetically identical to the parent. Eggs typically hatch in spring and develop into wingless females which then produce live young. After some generations of parthenogenesis, winged reproductive males and females are produced which mate and lay eggs.
5 Another Interesting Organism In approximately 15 of the Cnemidophorus species there are no males. They reproduce by parthenogenesis.Parthenogenesis is rare in vertebrates. The offspring of parthenogenic lizards are clones, identical to the mother.
6 Human Cloning1998 MiceUnited Nations (Nov. 20, 2001) - A key General Assembly committee backed a resolution calling for a treaty to ban the cloning of human beings, saying it was "contrary to human dignity.“ Under the draft resolution, a group would meet twice next year to define what should be negotiated in an international convention to ban reproductive cloning.1997 Dolly2000 Monkey Business
7 Box 9.3, Figure 1But something else is happening: genetic recombinationBACTERIAL CONJUGATION AND RECOMBINATION1. Hfr cells contain genes that allow them to transfer some or all of their chromosome to another cell.Hfr cellNormal cell2. Conjugation tube connects Hfr cell to normal cell. Copy of Hfr chromosome begins to move to recipient cell.Conjugation tube3. Homologous sections of chromosome synapse.Box 9.3, Figure: 1Caption:Recombination occurs in bacteria when a section of an Hfr chromosome enters a non-Hfr cell and integrates into its chromosome via crossing over.4. Cells separate. Section of Hfr chromosome integrates into recipient chromosome by crossing over.
8 Some comparisons between asexual and sexual reproduction Figure 9.9Some comparisons between asexual and sexual reproductionAsexual reproductionSexual reproductionGeneration 1Generation 2Figure: 9.9Caption:In this diagram, each female symbol and male symbol represents an individual. In the hypothetical example given here, every individual produces four offspring over the course of their lifetime, sexually reproducing individuals produce half males and half females, and all offspring survive to breed. Question How many asexually produced offspring would be present in generation 4? How many sexually produced offspring?Generation 3So, what good are males???
9 Genetic Recombination: Sexual Reproduction What are the benefits?Two copies of each gene (provides instructions)“Sharing” of beneficial genes“Infinite” number of combinations (variation)
10 Genetic Recombination: Sexual Reproduction What are the Costs?Courtship expensesTwo parents investing resources“Complicated” process to make gametesDangerous!
11 Genetic Recombination: Sexual Reproduction What are the Costs?Courtship expensesTwo parents investing resources“Complicated” process to make gametesDangerous!
12 Genetic Recombination: Sexual Reproduction What are the Costs?Courtship expensesTwo parents investing resources“Complicated” process to make gametesDangerous!
13 Genetic Recombination: Sexual Reproduction What are the Costs?Courtship expensesTwo parents investing resources“Complicated” process to make gametesDangerous!
14 Life Cycle Strategies Involving Sexual Reproduction Diploid Dominant (two copies of each chromosome)Haploid Dominant (one copy of each chromosome)Alteration of Generations
15 Figure 9.7a Diploid dominant 2n MEIOSIS: 2n >> n Diploid adultMITOSISFERTILIZATIONMEIOSIS:2n >> nHaploid gametes (n)Diploid zygoteDiploid dominantFigure: 9.7aCaption:(a) In animals, the gametes are the only haploid cells. Meiosis occurs in special reproductive tissues.2n
16 Figure 9.7b Haploid dominant MEIOSIS MITOSIS Haploid cell Diploid cell Caption:(b) In many algae, the fertilized egg is the only diploid cell. When this cell undergoes meiosis, the haploid cells that are produced go on to form a multicellular adult.Haploid adultMITOSISFERTILIZATIONHaploid gametes
17 Alternation of generations Figure 9.7c, upperAlternation of generationsMEIOSISMITOSISHaploid cellsDiploid plantHaploid gametesFigure: 9.7c, upperCaption:(c) In land plants and some algae, there is a multicellular diploid stage and a multicellular haploid stage. Typically, one of these two stages is larger in size and longer in life span than the other. In ferns, the diploid stage is more prominent; in mosses the haploid stage is more prominent.Haploid plantDiploid cellMITOSISMITOSISFERTILIZATIION
18 Figure 9.10aEvidence for the benefits of sexual reproduction: resistanceSnails subject to parasitism by trematode worms (Lively)Figure: 9.10aCaption:(a) Potamopyrgus antipodarum is a species of freshwater snail native to New Zealand. Some individuals in this species reproduce only sexually, while others reproduce only asexually.
19 Frequency of infection by parasites Figure 9.10bAre genetically diverse populations more resistant to parasites?0.400.300.200.15Male frequency0.100.05Figure: 9.10bCaption:(b) The x-axis (abscissa) on this graph plots the proportion of snails infected with trematode worms in a population while the y-axis (ordinate) plots the proportion of individuals in the same population that are male. (The proportion of males is an index of how many individuals reproduce sexually.)0.010.000.000.050.150.300.50Frequency of infection by parasites
20 Meiosis is a Special Type of Cell Division that Occurs in Sexually Reproducing Organisms Meiosis reduces the chromosome number by half, enabling sexual recombination to occur.Meiosis of diploid cells produces haploid daughter cells, which may function as gametes. (Fig. 9.2a-c, 9.3)
21 Figure 9.2cA full complement of chromosomes is restored during fertilization.Female gameten = 23 in humansMale gameten = 23 in humansFertilizationDiploid offspring contains homologous pair of chromosomesFigure: 9.2cCaption:Meiosis reduces chromosome number by one-half. In diploid organisms, the products of meiosis are haploid.
22 Homologous pair of premeiotic chromosomes Figure 9.2aEach chromosome replicates prior to undergoing meiosis.Maternal chromosomePaternal chromosome(n = 23 in humans)(n = 23 in humans)Duplication inS phaseSister chromatidsFigure: 9.2aCaption:Meiosis reduces chromosome number by one-half. In diploid organisms, the products of meiosis are haploid.CentromereHomologous pair of premeiotic chromosomes
23 Sister chromatids separate at meiosis II Figure 9.2bDuring meiosis, chromosome number in each cell is reduced.Parent cell contains homologous pair of chromosomesMEIOSIS IHomologs separateat meiosis IDaughter cells contain just one homologMEIOSIS IISister chromatids separate at meiosis IIFigure: 9.2bCaption:Meiosis reduces chromosome number by one-half. In diploid organisms, the products of meiosis are haploid.Four daughter cells contain one chromosome each. These cells become gametes.
24 Figure 9.3, left PRIOR TO MEIOSIS MEIOSIS I Homologous chromosomes separate.Chromosomes replicate, forming sister chromatids.Tetrad (4 chromatids from homologous chromosomes)Sister chromatidsChiasmaFigure: 9.3, LeftCaption:Exercise Label prophase, metaphase, anaphase, and telophase cells of meiosis I and meiosis II.1. Chromosomes replicate in parent cell.2. Synapsis of homologous chromosomes. Crossing over of non-sister chromatids.3. Tetrads migrate to middle of cell.4. Homologs separate.
25 Figure 9.3, right MEIOSIS II Sister chromatids separate Caption:Exercise Label prophase, metaphase, anaphase, and telophase cells of meiosis I and meiosis II.5. Cell divides.6. Chromosomes begin moving to middle of cell.7. Chromosomes line up at middle of cell.8. Sister chromatids separate.9. Cell division results in four daughter cells.
26 Meiosis is a Special Type of Cell Division that Occurs in Sexually Reproducing Organisms Meiosis reduces the chromosome number by half, enabling sexual recombination to occur.Gametes undergo fertilization, restoring the diploid number of chromosomes in the zygote.23 pairs of chromosomes in humansBut what about the difference in sizebetween the egg and sperm?Can be “extrachromosomal” factors in cytoplasm of egg:Mitochondria, chloroplasts, infectious agents, chemicals
27 Box 9.1 Figure 1 Box 9.1 Figure 1 Caption: Chromosomes undergoing mitosis are arranged randomly when first observed with the microscope. To determine a karyotype, a technician groups chromosomes by pairs and arranges them by number, as shown here. Question Is this human karyotype normal or does it reveal the presence of an extra chromosome?
28 Figure 9.1a,b 12 types of chromosomes in the lubber grasshopper kadjXihfcgEach type of chromosome has two homologs.Figure: 9.1a,bCaption:(a) Letters are placed next to each of the 12 distinct types of chromosomes found in lubber grasshopper cells. Note there are two of each type of chromosome. (b) The two members of a chromosome pair are called homologs. In this drawing, homologous chromosomes are indicated in blue and red.ekbdajfXihcg
29 Meiosis is a Special Type of Cell Division that Occurs in Sexually Reproducing Organisms Meiosis and fertilization introduce genetic variation in several ways:Independent assortment of homologous pairs at metaphase I:Each homologous pair can orient in either of two ways at the plane of cell division. (Fig. 9.5a,b)The total number of possible outcomes = 2n (n = number of haploid chromosomes). (Fig. 9.6)Crossing over between homologous chromosomes at prophase I.
30 Figure 9.5a Hypothetical example Eye color Hair color Gene that contributes to brown eyesGene that contributes to blue eyesGene that contributes to black hairGene that contributes to red hairFigure: 9.5aCaption:(a) In this hypothetical example, genes that influence hair color and eye color in humans are located on different chromosomes.Maternal chromosomePaternal chromosomeMaternal chromosomePaternal chromosome
31 Figure 9.5bDuring meiosis I, tetrads can line up two different ways before the homologs separate.ORFigure: 9.5bCaption:(b) This diagram shows how gametes with different combinations of genes result from separation of homologous chromosomes during meiosis I.Brown eyes Black hairBlue eyes Red hairBrown eyes Red hairBlue eyes Black hair
32 Figure 9.6Crossing overEVEN SELF-FERTILIZATION LEADS TO GENETICALLY VARIABLE OFFSPRING because of crossing overFigure: 9.6Caption:This example shows some of the possible results of self-fertilization in an organism with four chromosomes (2n = 4). Exercise To the last line in this figure, add sketches showing the chromosome complements in additional offspring produced by selfing.1. Parent cell with four chromosomes.2. Crossing over during meiosis I.3. Homologs separate. (Pairing of chromosomes depends on independent assortment.)5. Offspring produced by selfing (only some of the possibilities shown.)4. Gametes produced by meiosis II.
33 Box 9.2, Figure 1a,b: Crossing over involves breakage and reunion of chromatids Shape of chromosome 9 varies in two maize strainsKnobNo knobLongShortStrain 1Strain 2Genes on chromosome 9 also varyBox 9.2, Figure 1a,bCaption:(a) In certain strains of maize, the size and shape of chromosome 9 differs. (b) The distinctive versions of chromosome 9 also contain distinctive genes that affect the color and texture of kernels in adult maize plants.Colored kernelsColorless kernelsWaxy kernelsStarchy kernelsStrain 1Strain 2
34 Box 9.2, Figure 1c Predictions of crossing over hypothesis If crossing over results in exchange of genetic material between two chromosomes, the products of meiosis will look like this:Products of meiosisChromosome shape:Box 9.2, Figure 1cCaption:(c) These diagrams show the types of gametes and offspring traits that should occur if crossing over results in the physical exchange of chromosome segments.Long with knobShort with knobLong with no knobShort with no knobTraits contributed to offspring:Colored, waxy kernelsColored, starchy kernelsColorless, waxy kernelsColorless, starchy kernelsExperimental results support these predictions
35 Figure 9.4c Figure: 9.4c Caption: Question and Exercise (c) Is this meiosis I or II? What phase?
36 Figure 9.4b Figure: 9.4b Caption: Question and Exercise (b) What stage of meiosis I is illustrated here? Is this cell haploid or diploid?
37 Figure 9.4d Figure: 9.4d Caption: Question and Exercise (d) What is happening in this photograph?
38 The Consequences of Meiotic Mistakes Nondisjunctions occur when homologous chromosomes fail to separate at meiosis I or when chromatids fail to separate at meiosis II.Fertilization can result in embryos that are 2n (a “trisomy”) or 2n - 1. (Fig. 9.11)Abnormal copy numbers of one or more chromosomes is usually, but not always, fatal (Example: Down syndrome). (Fig. 9.12)Human survivors: trisomics = 13, 18, 21
39 Figure 9.11NONDISJUNCTION at Meiosis I: most common cause, weak meiosis Ialignment checkpoint in females???n + 1n + 1n – 12n = 4 n = 2n – 1Figure: 9.11Caption:If homologous chromosomes fail to separate during meiosis I, the gametes that result will have an extra chromosome or lack a chromosome. Exercise Nondisjunction can also occur during meiosis II, after meiosis I has proceeded normally. Starting with a parent cell like the one shown here, make a diagram showing each step in meiosis when one set of sister chromatids fails to disjoin at meiosis II. How many of the resulting gametes are normal? How many have an extra chromosome or lack a chromosome?1. Meiosis I starts normally. Tetrads line up in middle of cell.2. Then one set of homologs does not separate (= nondisjunction).3. Meiosis II occurs normally.4. All gametes have an abnormal number of chromosomes--either one too many or one too few.
40 Incidence of Down syndrome per number of births Figure 9.121 46Incidence of Down syndrome per number of births1 1001 290Figure: 9.12Caption:This graph plots mother’s age (on the x-axis) versus the incidence of Down syndrome, expressed as the number of affected infants per number of births. Question Suppose that you are an obstetrician. Based on these data, at what age would you recommend that pregnant mothers undergo procedures to check the karyotype of the embryos they carry?1 8801 12001 23001 160028323742202447Age of mother (years)
41 Other Consequences of Meiosis Polyploidy can occur when whole sets of chromosomes fail to separate at meiosis I or II.The resulting 2n gametes, if fertilized by normal sperm, create 3n zygotes (triploid).Organisms with an odd number of chromosome sets cannot produce viable gametes (Example: seedless fruits).3n = 2X1 chromosome separationat meiosis I = unbalanced gametes,undeveloped seeds
42 So where does this take us? How do mitosis and meiosis figure into the passage of genetic information?What are “patterns of inheritance”?How do genes determine organismic characteristics
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