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Chapter 13 – Campbell’s 6th Edition

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1 Chapter 13 – Campbell’s 6th Edition
Meiosis and Sexual Life Cycles

2 Definitions Heredity:
transmission of traits from generation to the next Variation: slight differences in appearance Genetics: scientific study of heredity and hereditary variation

3 Genes Genes: coded information in the form of hereditary units (lots of genes on each chromosome) Where else can you find DNA beside the nucleus of the cell? Mitochondria Chloroplast

4 Asexual Reproduction Asexual reproduction
single individual is sole parent and passes copies of all its genes to its offspring Clone the offspring of asexual individuals

5 Sexual reproduction Two parents give rise to offspring with unique combinations of genes; results in more variation

6 Animals Life Cycle Plants and some algae Fungi and some algae
sequence of stages from an organisms conception to production of its own offspring Animals

7 More Vocab somatic cell: body cells; any cell other than sperm or ovum
karyotype: micrograph of the 46 human chromosomes in which they are lined up in pairs starting with the longest homologous chromosomes: same length, centromere position, staining pattern; carry genes governing the same inherited characters sex chromosomes: X and Y chromosomes autosomes: all non-sex chromosomes (1 through 22)

8 Karyotype


10 Meiosis and Sexual Reproduction
Sexual Reproduction – chromosomes of two parents combine to form offspring 23 23 + (N) + Gametes Fertilization (2N) 46 Zygote

11 About Chromosomes (2N) = diploid – any cell with 2 complete sets of chromosomes (N) = haploid – a cell with 1 complete set of chromosomes Zygote (2N) – egg cell after fertilzation = egg + sperm Each chromosome in egg has a matching chromosome from sperm Homologous Pairs – matching chromosomes

12 Homologous pairs chromosomes occur in pairs one set from each parent
Diploid or 2N Cells that contain both sets of chromosomes. Haploid =1N Sex cells have only half the chromosome number

13 Just before Meiosis begins, during interphase identical sister chromatids are attached at the centromere, and centrioles have been duplicated. Centrioles

14 Meiosis: Prophase I During Prophase I: chromosomes condense
nucleus breaks down spindle fibers form Homologous chromosomes form tetrads (fours)

15 Meiosis: Prophase I the chromosomes condense
centrioles move to opposite poles of the parent cell and begin building the spindle microtubules. the nuclear envelope breaks down

16 Meiosis: Prophase I Homologous chromosomes pair up, forming tetrads.

17 Meiosis: Prophase I Homologous chromosomes pair up, forming tetrads...

18 Meiosis: Prophase I …. and crossing over may occur.
Crossing over- pieces of DNA are exchanged with the matching homologous chromosome

19 Meiosis: Prophase I centrioles begin building the spindle fibers.

20 Meiosis: Prophase I Spindle fibers grab each chromosome at the centromere. Move the chromosomes towards the poles.

21 Meiosis: Metaphase I During Metaphase I:
Homologous chromosomes line up in the middle. Equator = metaphase plate

22 Meiosis: Metaphase I Each pair is assorted independently; this
means that the maternal homolog in each pair randomly faces up or down. And this pair could have assorted like this. So this pair could have assorted like this.

23 Meiosis: Anaphase I During Anaphase I: Homologous pairs of separate.
Sister chromatids remain attached at the centromere.

24 Meiosis: Anaphase I

25 Meiosis: Anaphase I

26 Meiosis: Telophase I During Telophase: spindle fibers break down
new nuclear membrane forms

27 Meiosis: Telophase I the spindle fibers break down

28 Meiosis: Telophase I new nuclear membrane forms around each
group of chromosomes

29 Cytokinesis: Splitting of the cytoplasm

30 Now these two haploid cells will begin Meiosis II; in this division, sister chromatids will separate.

31 Meiosis: Prophase II Meiosis II is very much like Mitosis.
During Prophase II: nuclear membrane breaks spindle fibers reform

32 Meiosis: Prophase II the nuclear membrane breaks down

33 Meiosis: Prophase II centrioles move to opposite poles of the parent cell and begin building new spindle fibers

34 Meiosis: Prophase II

35 Meiosis: Prophase II centrioles begin building the spindle fibers

36 Meiosis: Prophase II The spindle fibers
attach to the chromosomes at the centromere

37 Meiosis: Metaphase II The spindle fibers
move the chromosomes to the center (metaphase plate) of the cell.

38 Meiosis: Anaphase II Sister chromatids separate.

39 Meiosis: Anaphase II

40 Meiosis: Telophase II During Telophase II:
the spindle fiber break down nuclear membrane reforms around each group of chromosomes

41 Meiosis: Telophase II the spindle fibers break down

42 Meiosis: Telophase II new nuclear membrane form around each group of chromosomes

43 Cytokinesis: Result: Four non-identical haploid cells are formed.



46 Mitosis vs. Meiosis

47 A comparison of mitosis and meiosis
Mitosis and Mieosis Chromosomes replicate only once Mitosis Cell divides once Produces 2 identical daughter cells Meiosis Cell divides twice Daughter cells with half the number of chromosomes Daughter cells are not all alike Produces 4 cells (gametes)

48 Independent Assortment

49 Crossing Over

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