Download Genetic recombination

11/27/2014
Genetic
recombination
Genetic recombination

Obtaining of new gene combinations by
rearrangements in genetic material:



Between two DNA molecules
Between two different chromosomes
Between two sets of chromosomes
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Biological importance of
recombination

Genetic variability

Natural selection

Biologic evolution
Recombination and phenotype
consequences






Genetic polymorphism
Normal phenotypic polymorphism
Different reaction to environment (drugs,
food, toxins...)
Susceptibility to infections
Predisposition to diseases (cancers,
diabetes...)
Abnormal phenotypic polymorphism
Types of recombination

Genomic – between ♀ and ♂
genomes


23 chrs ♀ + 23 chrs ♂ = 46
Chromosomal



During
fertilisation
Inter-chromosomal – between nonhomologous chromosomes;
Intra-chromosomal – between
homologous chromosomes
Gene – between two alleles by
gene fusion
During
meiosis
During
meiosis
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?

What is fertilization?


Fusion of two sexual cells of different origin
(haploid gametes; 23 chrs)  formation of
zygote (diploid cell 46 chrs).
What is meiosis?

Formation of haploid cells called gametes (by
reductional division a cell with 46 chrs 
makes haploid cells with 23 chrs)
Passing of genetic material from parents to children
Mitosis,
differentiation,
growing
Mitosis,
differentiation,
growing
Copil
(2n)
Adulţi
(2n)
Zigot
(2n)
Meiosis
Sperm (n)
Fertilization
Egg (n)
OVOGENESIS
SPERMATOGENESIS
Peculiarities of segregation of chromosomes in meiosis
during ovogenesis and spermatogenesis
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Mitosis vs. Meiosis
46 SC chrs
46 SC chrs
Replication
Replication
46 BC chrs
46 BC chrs
Mitosis
46 SC
chrs
Meiosis
46 SC
chrs
23 BC
chrs
I
23 BC
chrs
II
Somatic cells
23 SC
chrs
23 SC
chrs
23 SC
chrs
23 SC
chrs
Sexual cells = gametes
2n=2c
Mitosis
Meiosis
! Bivalents at equator
2n=4c
MI
M
! BC Chrs to poles
AI
A
TI
T
2n=2c
! n=2c
MII
2n=2c
AII
TII
! MC Chrs to
poles
! n=c
Meiosis

I division – reductional (2n=4cn=2c)





Prophase I
Metaphase I
Anaphase I
Telophase I
II Division – equational (n=2cn=c)




Prophase II
Metaphase II
Anaphase II
Telophase II
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Meiosis I – reductional
Prophase I
 Condensation of chromosomes
 Formation of spindle
 !!! Conjugation of homologous
chromosomes  bivalents
 !!! Crossing-over  intra-chromosomal
recombination
 There are 5 phases: L, P, Z, D, D
Prophase I
Leptotene
Chromatin
condensation
Zygotene
!!! Conjugation
of homologous
chromosomes
Pachytene
Diplotene
Diakinezis
!!! Crossingover
Pushing of
chromosomes
Chiasma
termination
Conjugation of homologous
chromosomes
♀




♂
Takes place during prophase I
Synapses of homologous
chromosomes
Ensured by synaptonemal complex
Importance – formation of bivalents
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Synaptonemal complex
Scaffold
Chromatin of
paternal sister
chromatids
Recombination
nodules
Chromatin of
maternal sister
chromatids
Crossing-over




Takes place during prophase I
Exchange of fragments between
homologous chromosomes  intrachromosomal recombination
Determined by synaptonemal complex
Importance – genetic variability
Crossover
gametes
Non-crossover
gametes
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Molecular mechanism of
crossing-over
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Metaphase I


Bivalents at equator
!!! Random orientation of chromosomes to
poles
Important
or
Anaphase I



Disjunction of homologous chromosomes
Migration of BC chromosomes to poles (n
chromosomes to each poles)
!!! Independent combination of nonhomologous chromosomes = interchromosomal recombination  2n
combination
or
AbC
aBc
or
or
ABC
abc
Abc
aBC
ABc
abC
Interchromosomal recombination




Takes place during anaphase I
Between non-homologous maternal and
paternal chromosomes
Random separation of non-homologous
chromosomes
Importance  genetic variability of
gametes
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Telophase I



Reorganization of two nuclei (n=2c)
Citokinesis
Two gametocytes (haploid,
chromosomes BC)  !!! Reduction of
number of chromosomes
n=2c
2n=4c
n=2c
Interkinesis

Preparation to second division (meiosis II)
Meiosis II – equational division



Prophase II
Formation of spindle
Maturation of kinetocores
and
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Metaphase II

At equator SC chromosomes
and
Anaphase II
Longitudinal cleavage of centromere
Disjunction of chromatids
Migration of SC chromosomes (n=c chrs)



and
Telophase II



Reorganization of nuclear envelopes and
formation of haploid nuclei (n=c)
Cytokinesis
4 haploid gametes
n=2c
II div
I div
n=c
n=c
II div
n=c
2n=4c
n=2c
n=c
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Biological importance of meiosis



Maturing of gametes
Genetic recombination
Multiplication of gametes
n=2c
n=c
II div
I div
n=c
II div
n=c
2n=4c
n=2c
Ovogenesis
Ovogonia
n=c
Spermatogenesis
Spermatogonia
Replication
Replication
1st spermatocyte
1st ovocyte
Meiosis I (reductional)
2nd ovocyte
Meiosis I (reductional)
Polar body
2nd spermatocytes
Meiosis II (equational)
Meiosis II (equational)
Egg
Spermatides
Spermatozoon
Polar bodies
Formation of
sperms
Fecundation)
Zygote
Spermatozoon
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