Meiosis and Sexual Reproduction. Chapter 11 Loulousis

Transcription

1 Meiosis and Sexual Reproduction Chapter 11 Loulousis

2 Meiosis - Phenomena Parents can produce many types of offspring. Families will have resemblances, but no two are exactly alike

3 Objectives Compare and contrast asexual and sexual reproduction by discussing advantages and disadvantages of both. Describe the different types of asexual reproduction Distinguish between haploid and diploid. Explain why its important for a gamete to be haploid.

4 Reproduction Process of producing offspring 1. Asexual Reproduction (cells divide by mitosis) 1. Binary fission 2. Fragmentation 3. budding 2. Sexual Reproduction (cells go through meiosis to make gametes)

5 Asexual Reproduction Offspring is genetically identical to parent (disadvantage) Occurs quickly (advantage) Many prokaryotes and some unicellular eukaryotes use this method

6 1.Binary fission Organism splits into two or more individuals of about equal size

7 2.Fragmentation Body breaks into several pieces Some or all of pies re-grow missing body parts

8 3. Budding New individual grows from side of existing organism and breaks off Is smaller in size than parent

9 Sexual Reproduction Uses Meiosis Two separate parents give genetic material to produce offspring Advantage: Offspring is genetically different from parents Disadvantage: takes longer, have to find a mate

10 Genetics Overview Every cell has DNA, DNA condenses and forms chromosomes Genes are located on chromosomes and control the traits of the individual The number of chromosomes depends on the species Humans have 46 chromosomes

11 Types of Cells Germ cell: specialized for sexual reproduction, makes sex cells (gametes) Examples: ovary cells or testis cell Somatic cell: all body cells except germ cell Examples: skin, nerve, stomach cells

12 Haploid vs. Diploid Each parent makes a gamete, or reproductive cell (egg or sperm) Gametes have half the number of chromosomes or 1 set of unpaired chromosomes (haploid, 1n) other cells in the body have two sets of chromosomes (diploid, 2n) In humans : 1n= 23 and 2n= 46

13 Fertilization The fusion of a haploid sperm and haploid egg to form a diploid zygote. A zygote is a fertilized egg n=23 egg sperm n=23 2n=46 zygote

14 Stop and Think 1. How are gametes and zygotes related? 2. What is one thing that all types of asexual reproduction have in common? 3. What would happen if the gametes of sexually reproducing organisms were diploid instead of haploid? Explain. 4.Give two differences between sexual and asexual reproduction.

15 Homologous Chromosomes Chromosomes that have the same kinds of genes, similar in size and structure Each diploid cell has a 23 pairs One homolog comes from mom and the other from dad making the homologous pair

16 Karyotype A method of organizing the chromosomes of a cell in relation to number, size, and banding pattern.

17 Humans have 23 Sets of Homologous Chromosomes Each Homologous set is made up of 2 Homologues. Homologue Homologue

18 Autosomes (The Autosomes code for most of the offspring s traits) In Humans the Autosomes are sets 1 22 Autosomes have genes that do not determine sex

19 Sex Chromosomes The Sex Chromosomes code for the sex of the offspring. ** If the offspring has two X chromosomes it will be a female. ** If the offspring has one X chromosome and one Y chromosome it will be a male. In Humans the Sex Chromosomes are the 23 rd set XX chromosome - female XY chromosome - male

20 Boy or Girl? The Y Chromosome Decides X chromosome Y chromosome

21 Let's Review Vocabulary Matching sets of chromosomes are called pairs 2. Egg and sperm combine to make a 3. Egg and sperm are both known as 4. A cell that only has half of a set of chromosomes is said to be. 5. Genes are located on

22 Objectives 1. To understand the importance of chromosome number and how incorrect chromosome number affects living organisms function.

23 Bellringer What happens when there is an incorrect number of chromosomes in a zygote? The organism has a disorder, disease, or could die

24 Chromosome Number Matters! Genetic Diseases and Syndromes can result with either an extra chromosome or missing chromosome This is a numerical abnormality Many genetic disease result due to structural abnormalities affecting genes

25 Non-disjunction Non-disjunction is the failure of homologous chromosomes, or sister chromatids, to separate during meiosis. Non-disjunction results with the production of zygotes with abnormal chromosome numbers remember. An abnormal chromosome number (abnormal amount of DNA) is damaging to the offspring.

26 Non-disjunctions usually occur in one of two fashions. The first is called Monosomy, the second is called Trisomy. If an organism has Trisomy 18 it has three chromosomes in the 18 th set, Trisomy 21. Three chromosomes in the 21 st set. If an organism has Monosomy 23 it has only one chromosome in the 23 rd set.

27 Common Non-disjunction Disorders Down s Syndrome Trisomy 21 Turner s Syndrome Monosomy 23 (X) Kleinfelter s Syndrome Trisomy 23 (XXY) Edward s Syndrome Trisomy 18

28 Down Syndrome-Trisomy 21 Short, broad hands Stubby fingers Rough skin Impotency (erectile dysfunction)in males Intellectual disability Small round face Protruding tongue Short lifespan

29 Turners Syndrome-Monosomy 23 (X) 96-98% do not survive to birth No menstruation No breast development No hips Broad shoulders and neck

30 Klinefelter s Syndrome-Trisomy 23 (XXY) Scarce beard Longer fingers and arms Sterile Delicate skin Low intellectual ability Normal lifespan

31 Klinefelter s Syndrome XXY, male

32 Small head Intellectual disability Internal organ abnormalities 90% die before 5 months of age Edward s Syndrome-Trisomy 18

33 Amniocentesis An Amniocentesis is a prrocedure a pregnant woman can have in order to detect some genetics disorders..such as non-disjunction.

34 Amniotic fluid withdrawn Amniocentesis

35 21 trisomy Downs Syndrome Can you see the extra 21 st chromosome? Is this person male or female?

36 Bellringer Write a sentence using each of the following words: Haploid, diploid, zygote 1 SENTENCE, not three separate! THINK!

37 MEIOSIS Objectives 1.Define Meiosis 2. Summarize the events of Meiosis I and II 3.Explain how meiosis contributions to genetic variation

38 Meiosis Germ cells (which are diploid) produce gametes (which are haploid) through meiosis Meiosis: cell division by which gametes with half the number of chromosomes form Diploid (2n) haploid (n) Involves two nucleus divisions -meiosis I and meiosis II.

39 Meiosis Purpose: To create 4 unique haploid cells for the purpose of reproduction

40 Meiosis Occurs only in gonads (testes or ovaries). A germ cell will go through meiosis to make gametes. Spermatogenesis- makes sperm Oogenesis-makes eggs

41 Spermatogenesis human sex cell n=23 n=23 n=23 sperm 2n=46 diploid (2n) n=23 n=23 haploid (n) n=23 meiosis I meiosis II

42 Meiosis mouse testes Parent cell 1 st division 2 nd division 4 gametes

43 Oogenesis *** The polar bodies die only one ovum (egg) is produced from each primary oocyte.

44 Interphase I Meiosis is similar to Mitosis and starts the same way with Interphase. DNA is duplicated. Each duplicated chromosome consist of two identical sister chromatids attached at their centromeres. organelles replicate.

45 Meiosis I (four phases) four phases: a. prophase I b. metaphase I c. anaphase I d. telophase I

46 Prophase I Longest and most complex phase (90%). Chromosomes condense and become visible. Nuclear envelope breaks down. Synapsis occurs in preperation of crossingover: homologous chromosomes come together to form a tetrad. Tetrad is two chromosomes or four chromatids (sister and nonsister chromatids).

47 Prophase I spindle fiber Tetrad centrioles aster fibers

48 Prophase I - Synapsis Homologous chromosomes sister chromatids Tetrad sister chromatids

49 Homologous Chromosomes Pair of chromosomes (maternal and paternal) that are similar in shape and size. Homologous pairs carry genes controlling the same inherited traits. Position of a gene is called a locus Humans have 23 pairs of homologous chromosomes.

50 Homologous Chromosomes eye color locus eye color locus hair color locus hair color locus Paternal Maternal

51 Crossing Over Occurs in Prophase I Occurs between nonsister chromatids at the chiasmata. Chiasmata (chiasma) are the areas on chromosomes where of crossing over. Crossing over is when segments of nonsister chromatids break off and reattach to the other chromatid.

52 Crossing Over - variation nonsister chromatids Tetrad chiasmata: site of crossing over variation

53 Crossing Over One way that meiosis adds to genetic diversity by increasing the number of possible gene combinations in the resulting gametes

54 Shortest phase Metaphase I Tetrads align on the metaphase plate (equator). INDEPENDENT ASSORTMENT OCCURS: 1. Which chromosome of the homologous pair ends up on the left vs right side of equator is random 2.The randomness adds to genetic variation giving more possible gene combinations in the resulting gametes

55 Independent Assortment OR metaphase plate metaphase plate

56 Question: In terms of Independent Assortment - how many different combinations of sperm could a human male produce? Formula: 2 n Human chromosomes: 2n = 46 n = = ~8 million combinations

57 Homologous chromosomes separate and move towards the poles. Sister chromatids remain attached at their centromeres. Anaphase I

58 Telophase I Each pole now has haploid set of chromosomes or one chromosome from each pair of homologous chromosomes. Cytokinesis occurs and two haploid daughter cells are formed.

59 Telophase I

60 Meiosis Purpose: To create 4 unique haploid cells for the purpose of reproduction

61 Prophase II New spindle forms around chromosomes

62 Metaphase II Chromosomes line up at equator (metaphase plate) in both cells. Spindle is attached to centromers metaphase plate metaphase plate

63 Anaphase II Centromeres divide sister chromatids separate move to opposite poles

64 Telophase II Nuclei form. Nuclear envelope forms around chromosomes. Cytokinesis occurs. Remember: four (genetically different) haploid daughter cells are produced. gametes = sperm or egg

65 Telophase II

66 Random Fertilization Fertilization is the third method that adds to genetic variation from sexual reproduction It is a random process as to which sperm fertilizes an egg. Humans have about 70 trillion different combinations of egg to sperm match up x 2 23 = 70 trillion

67 Genetic Variation Made possible by sexual reproduction which rearranges genes in process called meiosis advantageous for a population because it s the raw material for natural selection. Helps them survive environmental change Population: group of organisms of same species that live in same area

68 Question What are the three sexual sources of genetic variation? 1. crossing over (prophase I) 2. independent assortment (metaphase I) 3. random fertilization Remember: variation is good!

69 Question: A cell containing 20 chromosomes (diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?

70 Answer: 10 chromosomes (haploid)

71 Question: A cell containing 40 chromatids at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes?

72 10 chromosomes Answer:

73 Sources s.ppt sion/meiosis.ppt ce/lifefunctionsandthecell/meiosis.ppt

74 Jeopardy Review dyx/jeopardy-reviewgame.php?gamefile=