Chapter 13 – Campbell’s 6 th Edition Meiosis and Sexual Life Cycles.
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Transcript of Chapter 13 – Campbell’s 6 th Edition Meiosis and Sexual Life Cycles.
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Chapter 13 – Campbell’s 6th Edition
Meiosis and Sexual Life Cycles
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Definitions
1) Heredity: transmission of traits from generation to the
next
2) Variation: slight differences in appearance
3) Genetics: scientific study of heredity and hereditary
variation
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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?
MitochondriaChloroplast
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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
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Sexual reproduction
Two parents give rise to offspring with unique combinations of genes; results in more variation
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Life Cyclesequence of stages from an organisms
conception to production of its own offspring
Animals
Fungi and some algaePlants and some algae
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More Vocab
1) somatic cell:body cells; any cell other than sperm or ovum
2) karyotype:micrograph of the 46 human chromosomes in which they are lined up in pairs starting with the longest
1) homologous chromosomes:same length, centromere position, staining pattern; carry genes governing the same inherited characters
2) sex chromosomes:X and Y chromosomes
3) autosomes:all non-sex chromosomes (1 through 22)
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Karyotype
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Meiosis and Sexual Reproduction
• Sexual Reproduction – chromosomes of two parents combine to form offspring
23
23
+
46
Gametes
Fertilization
Zygote
(2N)
(N) + (N)
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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
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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
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Just before Meiosis begins, during interphaseidentical sister chromatidsare attached at the centromere, and centrioles have been duplicated.
Centrioles
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Meiosis: Prophase I
During Prophase I:
• chromosomes condense• nucleus breaks down• spindle fibers form• Homologous chromosomes form tetrads (fours)
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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
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Meiosis: Prophase I
Homologous chromosomes pair up, forming tetrads.
Tetra =4
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Meiosis: Prophase I
Homologous chromosomes pair up, forming tetrads...
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Meiosis: Prophase I
…. and crossing over may occur.
Crossing over- pieces of DNA are exchanged with the matching homologous chromosome
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Meiosis: Prophase I
centrioles begin building the spindle fibers.
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Meiosis: Prophase I
Spindle fibers grab each chromosome at the centromere. Move the chromosomes towards the poles.
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Meiosis: Metaphase I
During Metaphase I:Homologous chromosomes line up in the middle.
Equator = metaphase plate
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Meiosis: Metaphase IEach pair is assortedindependently; this means that the maternal homolog in each pair randomly faces up or down.
So this pair could have assorted like this.
And this pair could have assorted like this.
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Meiosis: Anaphase I
During Anaphase I:
Homologous pairs of separate.
Sister chromatids remain attached at the centromere.
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Meiosis: Anaphase I
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Meiosis: Anaphase I
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Meiosis: Telophase I
During Telophase:
• spindle fibers break down •new nuclear membrane forms
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the spindle fibers break down
Meiosis: Telophase I
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Meiosis: Telophase I
new nuclear membrane forms around each group of chromosomes
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Cytokinesis:
Splitting of the cytoplasm
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Now these two haploid cells will begin Meiosis II; in this division, sister chromatids will separate.
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Meiosis II is very much like Mitosis.
Meiosis: Prophase II
During Prophase II:
• nuclear membrane breaks
• spindle fibers reform
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Meiosis: Prophase II
the nuclear membrane breaks down
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Meiosis: Prophase II
centrioles move to opposite poles of the parent cell and begin building new spindle fibers
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Meiosis: Prophase II
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Meiosis: Prophase II
centrioles begin building the spindle fibers
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Meiosis: Prophase II
The spindle fibersattach to the chromosomes at the centromere
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Meiosis: Metaphase II
The spindle fibersmove the chromosomes to the center (metaphase plate) of the cell.
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Meiosis: Anaphase II
Sister chromatids separate.
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Meiosis: Anaphase II
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Meiosis: Telophase II
During Telophase II:
• the spindle fiber break down •nuclear membrane reforms around each group of chromosomes
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Meiosis: Telophase II
the spindle fibers break down
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Meiosis: Telophase II
new nuclear membrane form around each group of chromosomes
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Cytokinesis:
Result: Four non-identical haploid cells are formed.
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Mitosis vs. Meiosis
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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)
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Independent Assortment
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Crossing Over