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Cellular reproduction part 2. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Somatic cells of each species contain a specific.

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Presentation on theme: "Cellular reproduction part 2. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Somatic cells of each species contain a specific."— Presentation transcript:

1 Cellular reproduction part 2

2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Somatic cells of each species contain a specific number of chromosomes –Human cells have 46, making up 23 pairs of homologous chromosomes MEIOSIS AND CROSSING OVER Chromosomes are matched in homologous pairs Chromosomes Centromere Sister chromatids Figure 8.12

3 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Homologous Chromosomes Humans have 23 pairs of homologous chromosomes –22 pairs – autosomes – found in both males and females –1 pair – sex chromosomes, XX = female, XY= male

4 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Homologous Chromosomes Matched pairs of chromosomes Similar in size, shape, and banding pattern Both carry genes controlling the same inherited characteristics (the version of the gene may be different) The genes are located at the same locus One chromosome of each pair is inherited from the mother, the other from the father

5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The human life cycle Figure 8.13 MEIOSISFERTILIZATION Haploid gametes (n = 23) Egg cell Sperm cell Diploid zygote (2n = 46) Multicellular diploid adults (2n = 46) Mitosis and development

6 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Human Life Cycle Diploid cells (2n) – cells that contain both homologous chromosomes. In humans the diploid number is 46. Haploid cells (n) – cells with one copy of each homologous chromosome. The gametes (egg and sperm) are haploid. In humans the haploid number is 23.

7 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Meiosis The division that reduces the number of chromosomes by half. In animals, meiosis results in the formation of haploid egg and sperm cells.

8 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.15

9 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.16.2

10 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Meiosis Two nuclear divisions occur: 1.Meiosis I a.During prophase I homologous chromosomes pair – synapsis b.During prophase I the paired chromosomes exchange chromosome parts – crossing over c.Homologous chromosomes are separated d.2 cells produced each containing one copy of each homologous chromosome

11 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.16.3

12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Meiosis 2.Meiosis II a.Not preceded by the replication of DNA b.Sister chromatids of each chromosome are separated c.Produces 4 haploid cells

13 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Meiosis Meiosis produces 4 cells that Are haploid Chromosome makeup of each is different from each other and the parent cell

14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.17

15 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

16 Meiosis Spermatogenesis Formation of sperm by meiosis Occurs in special cells (spermatogonia) in the testes All 4 haploid cells become sperm

17 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

18 Meiosis Oogenesis Formation of an egg by meiosis Occurs in special cells (oogonia) in the ovaries Unequal divisions of the cytoplasm during meiosis I and meiosis II result in the formation of 1 haploid egg and 3 haploid polar bodies Only the egg can be fertilized

19 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

20 Genetic Recombination Genetic Recombination – the production of gene combinations different from those carried by the parent There are 4 processes that contribute to genetic recombination.

21 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.18

22 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Independent Assortment of Chromosomes The large number of possible arrangements of chromosome pairs at metaphase I of meiosis leads to many different combinations of chromosomes in gametes –This results in 2 n possible combinations of gametes –For humans 2 n = 2 23 = 8 million possible combinations –http://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter28/animation__random_orientation_of_chromosomes_during_meiosis.htmlhttp://highered.mcgraw- hill.com/sites/0072495855/student_view0/chapter28/animation__random_orientation_of_chromosomes_during_meiosis.html Random fertilization also increases variation in offspring

23 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.17A, B Coat-color genesEye-color genes BrownBlack CE ce WhitePink CE ce CE ce Tetrad in parent cell (homologous pair of duplicated chromosomes) Chromosomes of the four gametes

24 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The differences between homologous chromosomes are based on the fact that they can carry different versions of a gene at corresponding loci Homologous chromosomes carry different versions of genes

25 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.18A Tetrad Chaisma Centromere

26 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings How crossing over leads to genetic recombination Figure 8.18B Tetrad (homologous pair of chromosomes in synapsis) Breakage of homologous chromatids Joining of homologous chromatids Chiasma Separation of homologous chromosomes at anaphase I Separation of chromatids at anaphase II and completion of meiosis Parental type of chromosome Recombinant chromosome Parental type of chromosome Gametes of four genetic types 1 2 3 4 Coat-color genes Eye-color genes

27 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.19 Animation (must insert Miller and Levine lecture cd ch11) Meiosis 1 Crossing over a closer lookCrossing over a closer look Meiosis II http://bcs.whfreeman.com/thelife wire/content/chp09/0902002.htmlhttp://bcs.whfreeman.com/thelife wire/content/chp09/0902002.html

28 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Genetic Recombination Crossing over The exchange of genetic information between 2 homologous chromosomes. Occurs during prophase I. Random fertilization Depends on which sperm cell and its chromosome combinations fertilizes which egg

29 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Preparation of a karyotype Figure 8.19 Blood culture 1 Centrifuge Packed red And white blood cells Fluid 2 Hypotonic solution 3 Fixative White Blood cells Stain 45 Centromere Sister chromatids Pair of homologous chromosomes

30 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings To study human chromosomes microscopically, researchers stain and display them as a karyotype –A karyotype usually shows 22 pairs of autosomes and one pair of sex chromosomes ALTERATIONS OF CHROMOSOME NUMBER AND STRUCTURE A karyotype is a photographic inventory of an individual’s chromosomes

31 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Abnormal chromosome count is a result of nondisjunction –Either homologous pairs fail to separate during meiosis I –http://www.sumanasinc.com/webcontent/an imations/content/mistakesmeiosis/mistakes meiosis.swfhttp://www.sumanasinc.com/webcontent/an imations/content/mistakesmeiosis/mistakes meiosis.swf 8.21 Accidents during meiosis can alter chromosome number Figure 8.21A Nondisjunction in meiosis I Normal meiosis II Gametes n + 1 n – 1 Number of chromosomes

32 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Or sister chromatids fail to separate during meiosis II Figure 8.21B Normal meiosis I Nondisjunction in meiosis II Gametes n + 1n – 1nn Number of chromosomes

33 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Fertilization after nondisjunction in the mother results in a zygote with an extra chromosome Figure 8.21C Egg cell Sperm cell n + 1 n (normal) Zygote 2n + 1

34 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings This karyotype shows three number 21 chromosomes An extra copy of chromosome 21 causes Down syndrome Connection: An extra copy of chromosome 21 causes Down syndrome Figure 8.20A, B

35 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.23 The chance of having a Down syndrome child goes up with maternal age

36 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Alterations of Chromosomes In most cases abnormal chromosome number results in spontaneous abortion long before birth. Nondisjunction in the sex chromosomes has less of an affect on survival

37 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Nondisjunction can also produce gametes with extra or missing sex chromosomes –Unusual numbers of sex chromosomes upset the genetic balance less than an unusual number of autosomes Connection: Abnormal numbers of sex chromosomes do not usually affect survival

38 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Table 8.1

39 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

40 Chromosome breakage can lead to rearrangements that can produce genetic disorders or cancer –Four types of rearrangement are deletion, duplication, inversion, and translocation Connection: Alterations of chromosome structure can cause birth defects and cancer

41 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 8.23A, B Deletion Duplication Inversion Homologous chromosomes Reciprocal translocation Nonhomologous chromosomes Deletion – a chromosome breaks and a fragment is lost. Seems to have the greatest affect. Duplication – the fragment joins to a homologous chromosome. Inversion – the fragment reattaches to the original chromosome but in reverse orientation. Least likely to produce harmful affects. Translocation– attachment of a chromosome fragment to a nonhomologous chromosome. May/may not be harmful.

42 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Alterations of Chromosomes Abnormalities in the structure of the chromosome may cause disorders (Figure 8.23A) 1.Deletion – a chromosome breaks and a fragment is lost. Seems to have the greatest affect. 2.Duplication – the fragment joins to a homologous chromosome.

43 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Alterations of Chromosomes 3.Inversion – the fragment reattaches to the original chromosome but in reverse orientation. Least likely to produce harmful affects. 4.Translocation (Figure 8.23B) – attachment of a chromosome fragment to a nonhomologous chromosome. May/may not be harmful.

44 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chromosomal changes in a somatic cell can cause cancer Figure 8.23C Chromosome 9 –A chromosomal translocation in the bone marrow is associated with chronic myelogenous leukemia Chromosome 22 Reciprocal translocation “Philadelphia chromosome” Activated cancer-causing gene


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