Meiosis -...
Transcript of Meiosis -...
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Meiosis
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Who discovered the importance of heredity?
Gregor Mendel
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Define heredity.
Heredity is the passing on of characteristics from parent to offspring.
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Define traits.
Traits represent the characteristics that are inherited.
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Define genetics.
Genetics is the branch of biology that studies heredity.
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Define gametes.
Gametes are the organism’s sex cells 2 types: sperms (y) and eggs (x)
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Define fertilization.
Fertilization is the union of male gametes and female gametes.
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Define zygote.
Zygote means a fertilized cell known as a “offspring”.
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VocabularyAlleles
alternatecombination of genes represented by
letters Only 3 types of letter combinations Example: hair color
(H) HH, hh, Hh
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Vocabulary
Homologous Chromosomes
pair of chromosomeshaving alleles or genes in the sameorder of arrangement.
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Practice of Homologous Chromosomes
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Vocabulary Continues
Crossing Over exchange of genetic
material between nonsister homologouschromosomes
results in new allele combinations
occurs only in prophase I of meiosis
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Sex Chromosomeschromosomes that
determine the sex of an organism only 1 pair of sex
chromosomesFemale:XX and
Male:XYcarries genetic
variations mutations
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How many pairs and numbers of chromosomes exist among humans?
Total Pairs and Numbers
23 pairs
46 chromosomes
Sex Chromosomes
Determines sex of an organism
(0.1%)
1 pair
2 chromosomes
Autosomes
Pairs of matching homologous chromosomes
(99.9%)
22 pairs
44 chromosomes
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Diploid versus HaploidParent Cell 2n
mitosis
Meiosis
I
2 Daughter Cells 2n
Diploid…2 sets of
chromosomes
Meiosis II
Meiosis IIMeiosis IIMeiosis II
4 Daughter Cells n
Haploid…1 set of
chromosomes
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Define meiosis.
Meiosis is the cell division that produces gametescontaining half the number of chromosomes as the parent cell.
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How many cell divisions occur during meiosis? Name them.
Meiosis I and Meiosis II
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What type of cells (diploid or haploid) form at the end of Meiosis I?
2 Diploid Cells…2 sets of chromosomes in
each
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What type of cells (diploid or haploid) form at the end of Meiosis II?
4 Haploid Cells…1 set of chromosomes
in each
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The Phases of Meiosis I
Visible chromosomes cannot be seen
DNA replicating (copying)
1.) Interphase I
Nucleus
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The Phases of Meiosis I
Chromosomes pair up and startbecoming visible
Crossing overtakes place
2.) Prophase I
Nuclear Membrane
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The Phases of Meiosis I
Chromosomes line up side by side(horizontal) at the metaphase plate (equator)
3.) Metaphase I
Means “middle”
Spindles
Centriole
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The Phases of Meiosis I
Chromosomes split apart
Sister chromatidsmove to oppositesides of centrioles(poles)
4.) Anaphase I
CentrioleSpindle
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The Phases of Meiosis I
Through cytokinesis, the parent cell divides into 2 diploiddaughter cells (2n)
5.) Telophase I
Two cells
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The Phases of Meiosis II
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The Phases of Meiosis II
Nuclear membrane begins to break down
Chromosomes pair up and startbecoming visible
2.) Prophase II
Nuclear Membrane
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The Phases of Meiosis II
Chromosomes line up vertically at the metaphase plate (equator)
3.) Metaphase II
Means “middle”
Spindles
Centriole
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The Phases of Meiosis II
Chromosomes split apart
Sister chromatidsmove to oppositesides of centrioles(poles)
4.) Anaphase II
Spindles
Centriole
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The Phases of Meiosis II
Through cytokinesis, the cells divides into 4haploid daughter cells (n)
5.) Telophase II
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Need to Understand
Crossing over means anygenetic variation that ONLYoccurs in Prophase I of meiosis cell division.
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Formula for Meiosis I & II
n = number of chromosomes present
2n
2n
2nParent
2 Diploid Cells
n
n
n
n
4 Haploid Cells
Meiosis I Meiosis II