biologia7
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Transcript of biologia7
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Meiosis
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44 XY 44 XX
44 XY
22 X
22 X
22 Y
44 XX
SPERMSOVULES
SEX DETERMINISM IN HUMANS
HETEROGAMETIC SEX
HOMOGAMETIC SEX
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4646
23
23
46
46
46 46
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Variability causes in Meiosis
1.Homologous Chromosomes Separation during ANAPHASE I.
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PROPHASE I
SYNAPSIS
CROSSING OVER
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A A A AB B b bC C C C
D D D D
E E e eFG
F F F
G g g
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AB
C
D
E
F
G
AB
C
D
e
F
g
AAb
C
D
e
F
g
b
C
D
E
F
G
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Variability causes in Meiosis2. Crossing over
RECOMBINATION OF GENES
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Random Crossing over between homologous chromosomes, as a result........Recombination
Recombination
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Imagine that Recombination takes place only in one pair of Chromosomes. From the mother cell after Meiosis would appear four types of ovules.
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Understanding Meiosis
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MEIOSIS I
MEIOSIS: A GENERAL VISION
MEIOSIS II
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Each body cell (Somatic Cell) contains two sets of chromosomes .One set comes from father and the another one comes from mother.
Human beings 46 Chromosomes.23 from father23 from mother.
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ABCD1EF3G2H9
ABCD1EF3G2H9 I
JKLMN1O1PQ
IJKLMN1O1PQ
mother`s chromosome
father`s chromosome
AbCD2EF1G2H9
AbCD2EF1G2H9
iJkL2mN1O3Pq
iJkL2mN1O3Pq
HOMOLOGOUS
They take genes for the same Traits but can take different versions.Observe the Example.
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SYNAPSIS
To match
matching
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Crossing over and Recombination
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The main events in Meiosis
2. Random Crossing over between homologous chromosomes
1.Homologous Chromosomes Separate during ANAPHASE I
RECOMBINATION OF GENES
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MITOSIS OR MEIOSIS. Why?
12
34
5
6
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HOMOLOGOUSHOMOLOGOUS
CHROMOSOMES ALIGN ALONG
METAPHASE PLATE
PROPHASE I
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d) Anaphase I
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PROPHASE II
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i) Anaphase II
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Variability causes in Meiosis
1. Crossing over
3.Separation of sister Chromatides during ANAPHASE II
2.Homologous Chromosomes Separation during ANAPHASE I
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AB
C
D
E
F
G
AB
C
D
e
F
g
AAb
C
D
e
F
g
b
C
D
E
F
G
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1. Crossing over
Exchange of Genetic Material between Homologous Chromosomes
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2.Homologous Chromosomes Separation during ANAPHASE I
Either
or
A B
A B
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A1A2
A1 A2
A3 A4 A3A4
ANAPHASE II
3.Separation of sister Chromatides during ANAPHASE II
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CHROMOSOME CROSSING-OVERA B A A B B
C C C C
REPLICATION
S
HOMOLOGOUS
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C C C C
CROSSING OVER
SYNAPSIS
matching
Chiasma
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C C C C
CROSSING OVER
SYNAPSIS
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C C C C
SYNAPSIS
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CCCCCC
GAMETES