Meiosis
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Transcript of Meiosis
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Meiosis
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Sex CellsGametes (germ cells)Eggs and Sperm
Somatic CellsAll other cells
Types of Human Cells
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Autosomes – same number in males and females
Sex Chromosomes – X or Y
Human females: XX
Human males: XY
Testosterone and other hormones from the Y make a male
Types of Chromosomes
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46 chromosomes(23 pairs)
Humans
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Describes how many sets of different chromosomes a cell has.
n = number of chromosomes in 1 set (haploid number)
Haploid Cells: 1nDiploid Cells: 2nIn humans, n = 23 (the
number of different chromosomes we have)
Ploidy
32/16
62
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Figure 13.5
KeyHaploid (n)Diploid (2n)
Egg (n)
Haploid gametes (n 23)
Sperm (n)
Ovary Testis
Mitosis anddevelopment
Diploidzygote(2n 46)
Multicellular diploidadults (2n 46)
MEIOSIS FERTILIZATION
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Figure 13.6
KeyHaploid (n)Diploid (2n)
Gametes
MEIOSIS FERTILIZATION
Zygote
MitosisDiploidmulticellularorganism
(a) Animals
n
n
n
2n 2n 2n 2n2n
n nn
n n
nn
n
nn
MEIOSIS
MEIOSIS
FERTILIZATION
FERTILIZATION
Mitosis Mitosis
Mitosis
Mitosis Mitosis
GametesSpores
Gametes
Zygote
Zygote
Haploid multi-cellular organism(gametophyte)
Diploidmulticellularorganism(sporophyte)
Haploid unicellular ormulticellular organism
(b) Plants and some algae (c) Most fungi and some protists
Plants and some algae exhibit an alternation of generations.
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In crossing over, nonsister chromatids exchange DNA segments.
Each pair of chromosomes forms a tetrad, a group of four chromatids.
Each tetrad usually has one or more chiasmata, X-shaped regions where crossing over occurred.
Crossing Over
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Figure 13.11-1Prophase Iof meiosis
Nonsister chromatidsheld togetherduring synapsis
Pair of homologs
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Figure 13.11-2Prophase Iof meiosis
Nonsister chromatidsheld togetherduring synapsis
Pair of homologs
Chiasma
Centromere
TEM
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Figure 13.11-3Prophase Iof meiosis
Nonsister chromatidsheld togetherduring synapsis
Pair of homologs
Chiasma
Centromere
TEMAnaphase I
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Figure 13.11-4Prophase Iof meiosis
Nonsister chromatidsheld togetherduring synapsis
Pair of homologs
Chiasma
Centromere
TEMAnaphase I
Anaphase II
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Figure 13.11-5Prophase Iof meiosis
Nonsister chromatidsheld togetherduring synapsis
Pair of homologs
Chiasma
Centromere
TEMAnaphase I
Anaphase II
Daughtercells
Recombinant chromosomes
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Down Syndrome
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Klinefelter’s Syndrome
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Cause: Nondisjunction