QQ 10/5/18 Copy the following into notebook:

Transcription

1 Chapter 13- Meiosis

2 QQ 10/5/18 Copy the following into notebook: Similarities: Differences:

3 Figure 13.1

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5 Living organisms are distinguished by their ability to reproduce their own kind Transmission of traits from one generation to another- inheritance, or heredity With inheritance there are both similarities and differences. Genetics is the study of heredity and variation

6 Parents endow their offspring with genesheredity units of DNA -Tens of thousands passed on to offspring -All the genes compose the genome Human Genome Project (2000) Cystic Fibrosis Gene Human gene mapping of major genetic conditions

7 Gametes- the cells used by plants and animals to pass on their genetic info *sperm/egg (pollen/egg) All genes can be found at a specific, corresponding location- Locus Locus point is specific and identified with designated (p, q, letters/numbers)

8 Information on paired genes from each parent (specific locus point)

9 Asexual reproduction- A single individual is a parent and passes on ALL of its genetic information by mitosis to a clone. Can be single or multicellular organism. Variation in family lines is caused by mutations.

10 Figure mm Parent Bud (a) Hydra (b) Redwoods Budding in a Hydra

11 Sexual reproduction- Variation is caused by both parents passing on a set of their genetic information that then combines. Meiosis *Makes GAMETES only Karyotyping- Matching up pairs of chromosomes from longest to shortest. These pairs are called homologous chromosomes or autosomes *in humans, homologous pairs #1-22 are the autosome; #23 are sex chromosomes- not considered homologous! (XX or XY)

12 APPLICATION Figure 13.3 TECHNIQUE Pair of homologous duplicated chromosomes 5 µm Centromere Sister chromatids Metaphase chromosome

13 Karyotypes (humans on left; cat on right)

14 A Dog s Karyotype

15 There are also two distinct chromosomes that might not match- sex chromosomes - Male- XY- Smaller amount of DNA - Sperm can either be X or Y - Female- XX - Egg is ALWAYS X

16 diploid germ cells in female diploid germ cells in male meiosis, gamete formation in both female and male: eggs X sperm Y X X fertilization: X X X XX XX Y XY XY sex chromosome combinations possible in the new individual 16 Fig. 11.2, p.170

17 Chapter 13- Meiosis Haploid cell (n)- Single set of chromosomes (in humans, n=23). Offspring receive one set from maternal (egg) side, another from paternal (sperm) Diploid cell (2n)- BOTH sets of chromosomes (in humans, 2n= 46) Cat n=? 2n=? Dog n=? 2n=?

18 Chromosome numbers: All are even numbers diploid (2n) sets of homologous chromosomes! Ploidy = number of copies of each chromosome. Diploidy 18

19 Key Haploid (n) Diploid (2n) Figure 13.5 Haploid gametes (n = 23) Egg (n) Sperm (n) MEIOSIS FERTILIZATION Ovary Testis Diploid zygote (2n = 46) Mitosis and development Multicellular diploid adults (2n = 46)

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21 Life Cycle begins when egg meets sperm and is fertilized (forms the zygote) - Zygote is diploid (2n) The only cells not produced by mitosis are the gametes AFTER FERTILIZATION = The zygote produces more somatic cells by mitosis and develops into an adult

22 Figure n = 6 Key Maternal set of chromosomes (n = 3) Paternal set of chromosomes (n = 3) Sister chromatids of one duplicated chromosome Centromere Two nonsister chromatids in a homologous pair Pair of homologous chromosomes (one from each set)

23 The Variety of Sexual Life Cycles The alternation of meiosis and fertilization is common to all organisms that reproduce sexually The three main types of sexual life cycles differ in the timing of meiosis and fertilization 2011 Pearson Education, Inc.

24 Alteration of Generations (plants and algae) Some plants undergo alternation of generations - has a diploid AND haploid multicellular stage of life Diploid stage- Sporophyte (produces spores, which do not have to fuse to create offspring) Haploid stage- Gametophyte (produces gametes)

25 Figure main types of sexual life cycles Key Haploid (n) Diploid (2n) n Gametes n Haploid multicellular organism (gametophyte) Haploid unicellular or multicellular organism MEIOSIS n FERTILIZATION n Mitosis MEIOSIS n n n Spores Gametes Mitosis n FERTILIZATION n Mitosis n n Gametes Mitosis n n 2n Diploid multicellular organism Zygote 2n Mitosis 2n Diploid multicellular organism (sporophyte) 2n Mitosis Zygote MEIOSIS FERTILIZATION 2n Zygote (a) Animals (b) Plants and some algae (c) Most fungi and some protists

26 Figure 13.6a Key Haploid (n) Diploid (2n) n Gametes n n MEIOSIS FERTILIZATION 2n Zygote 2n Diploid multicellular organism Mitosis (a) Animals

27 Plant and algae sexual life cycle: The diploid organism, called the sporophyte, makes haploid spores by meiosis. Each spore grows by mitosis into a haploid organism called a gametophyte and a gametophyte makes haploid gametes by mitosis! (already haploid so mitosis used to make more IDENTICAL haploid cells!) Fertilization of gametes results in a diploid sporophyte! 2011 Pearson Education, Inc.

28 Figure 13.6b Key Haploid (n) Diploid (2n) Haploid multicellular organism (gametophyte) Mitosis n Mitosis n n n Spores Gametes MEIOSIS n FERTILIZATION 2n Diploid multicellular organism (sporophyte) 2n Mitosis Zygote Moss reproduction video (b) Plants and some algae

29 Depending on the type of life cycle: either haploid or diploid cells can divide by mitosis However, only diploid cells can undergo meiosis! 2011 Pearson Education, Inc.

30 STEPS OF MEIOSIS VS. MITOSIS ANIMATION

31 KEY DIFFERENCE! Homologous pairs separate first 31

32 CROSSING OVER! 32

33 Sister Chromatids separate at centromeres 33

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35 Meiosis Meiosis- reduces the number of chromosome sets from diploid to haploid Two CONSECUTIVE cell divisions, Meiosis I and Meiosis II 4 daughter cells produced

36 Meiosis Interphase- Replication of genome and growth occur. Centrosomes replicate Meiosis stage Prophase I- 90% of total time of meiosis Chromosomes begin to condense Homologous chromosomes pair and match up by gene (forming a tetrad)

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38 Meiosis Crossing over- Where ever these homologous chromosomes match up, genetic information will switch to opposite chromosome Centrosome movement toward poles of cell Spindle formation and attachment of fibers Breakdown of nuclear envelope

39 Meiosis Metaphase I- Tetrads arrange on the metaphase plate, spindle is fully attached Anaphase I- Sister chromatids move toward poles Sister chromatids remain attached

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41 Meiosis Telophase I and Cytokenesis I Each cell will have sister chromatids Splitting and cytokensis Chromosomes might unwind, might not (depending on organism)

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43 Meiosis Prophase II- Spindle apparatus forms, movement of sisters towards metaphase plate Metaphase II- Spindle fibers attach to sisters at metaphase plate Anaphase II- Separation and migration of individual chromosomes toward poles Telophase II and Cytokenesis II- Nuclei form and chromosomes unwind

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45 Meiosis (top) vs. mitosis (bottom)

46 Meiosis What makes meiosis unique? 1) Synapses- process of attachment of homologous chromosomes - Crossing Over- genetic rearrangement - Chiasma (plural- chiasmata) physical manifestation of crossing over

47 Meiosis 2) Tetrads on metaphase plate 3) Separation of homologous chromosomes in Anaphase I, but sisters stay attached to each other

48 Meiosis Three mechanisms that contribute to genetic variation 1) Independent Assortment of chromosomes- random orientation of homologous pairs at Metaphase I - 50% of the homologous pair is maternal, 50% is paternal

49 Independent Assortment

50 Independent Assortment Which way is it going to be facing when pulled by the spindle? Law of Independent Assortment basically says every chromosome for himself To figure out how many possible combinations we can have, use 2 n. Humans = 2 23 = about 8 million combinations

51 Meiosis Three mechanisms that contribute to genetic variation 2) Crossing Over- produces recombinant chromosomes (from multiple origins) - DNA is switched between maternal and paternal chromosomes - In humans there are roughly 1-3 crossing over events per chromosome

52 Crossing Over

53 Meiosis Three mechanisms that contribute to genetic variation 3) Random Fertilization- The chance that you are sitting here is staggering. - Paternal side 2 23, maternal side 2 23 and we then multiply = about 70 trillion : 1 (and this does NOT take into account crossing over events)

54 Mitosis vs. Meiosis Comparing Mitosis and meiosis Just meiosis! 54

55 Figure 13.9b SUMMARY Property Mitosis Meiosis DNA replication Number of divisions Synapsis of homologous chromosomes Number of daughter cells and genetic composition Role in the animal body Occurs during interphase before mitosis begins One, including prophase, metaphase, anaphase, and telophase Does not occur Two, each diploid (2n) and genetically identical to the parent cell Enables multicellular adult to arise from zygote; produces cells for growth, repair, and, in some species, asexual reproduction Occurs during interphase before meiosis I begins Two, each including prophase, metaphase, anaphase, and telophase Occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion Four, each haploid (n), containing half as many chromosomes as the parent cell; genetically different from the parent cell and from each other Produces gametes; reduces number of chromosomes by half and introduces genetic variability among the gametes

56 Sister chromatid cohesion allows sister chromatids of a single chromosome to stay together through meiosis I (Protein complexes called cohesins are responsible for this cohesion) In mitosis, cohesins are cleaved at the end of metaphase In meiosis, cohesins are cleaved along the chromosome arms in anaphase I (separation of homologs) and at the centromeres in anaphase II (separation of sister chromatids) 2011 Pearson Education, Inc.

57 Origins of Genetic Variation Three mechanisms contribute to genetic variation 1. Independent assortment of chromosomes 2. Crossing over 3. Random fertilization 2011 Pearson Education, Inc.

58 Independent assortment Number of combinations: 2 n e.g. 2 chromosomes in haploid 2n = 4; n = 2 2 n = 2 2 = 4 possible combinations 58

59 Independent assortment 59

60 In humans e.g. 23 chromosomes in haploid 2n = 46; n = 23 2 n = 2 23 = ~ 8 million possible combinations! 60

61 Random fertilization At least 8 million combinations from Mom, and another 8 million from Dad >64 trillion combinations for a diploid zygote!!! 61

62 Crossing over Chiasmata sites of crossing over synapsis Exchange of genetic material between non-sister chromatids. Crossing over produces recombinant chromosomes. 62

63 Alterations in chromosome number and individual chromosomes Many mutations can occur during mitosis or meiosis that will affect the chromosome numbers or alter the information on individual chromosomes. Mutations can be harmful or beneficial to the organism Types of mutations include: Nondisjunction Deletion Duplication Inversion Translocation 63

64 Trisomy 21- Cause of Down Syndrome Nondisjunction animation 64

65 Various animations showing chromosomes alterations 65

66 Which of the following transmits genes from one generation of a family to another? a) DNA b) gametes c) somatic cells d) mitosis e) nucleotides 2011 Pearson Education, Inc.

67 Which of the following transmits genes from one generation of a family to another? a) DNA b) gametes c) somatic cells d) mitosis e) nucleotides 2011 Pearson Education, Inc.

68 Fertilization is to zygote as meiosis is to which of the following? a) mitosis b) diploid c) chromosome d) replication e) gamete

69 Fertilization is to zygote as meiosis is to which of the following? a) mitosis b) diploid c) chromosome d) replication e) gamete

70 Privet shrubs and humans each have a diploid number of 46 chromosomes per cell. Why are the two species so dissimilar? a) Privet chromosomes undergo only mitosis. b) Privet chromosomes are shaped differently. c) Human chromosomes have genes grouped together differently. d) The two species have different genes with different information.

71 Privet shrubs and humans each have a diploid number of 46 chromosomes per cell. Why are the two species so dissimilar? a) Privet chromosomes undergo only mitosis. b) Privet chromosomes are shaped differently. c) Human chromosomes have genes grouped together differently. d) The two species have different genes with different information.

72 Independent Assortment At what stage do chromosomes undergo independent assortment? How? a) meiosis I with the pairing of homologs b) anaphase I with the separation of homologs c) meiosis II with the separation of homologs d) meiosis I with metaphase alignment

73 Independent Assortment At what stage do chromosomes undergo independent assortment? How? a) meiosis I with the pairing of homologs b) anaphase I with the separation of homologs c) meiosis II with the separation of homologs d) meiosis I with metaphase alignment

74 Meiotic Phases In this cell, what phase is represented? a) mitotic metaphase b) meiosis I anaphase c) meiosis I metaphase d) meiosis II anaphase e) meiosis II metaphase

75 Disjunction What allows sister chromatids to separate in which phase of meiosis? a) release of cohesin along sister chromatid arms in anaphase I b) crossing over of chromatids in prophase I c) release of cohesin at centromeres in anaphase I d) release of cohesin at centromeres in anaphase II e) crossing over of homologues in prophase I

76 What are 3 ways in which gametes from one individual diploid cell can be different from one another?

77 What are 3 ways in which gametes from one individual diploid cell can be different from one another? mutation, crossing over, independent assortment

78 Rate and Process Prophase I of meiosis is generally the longest phase of meiosis. Why might this be?