5. genetic variation
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LOGO
2. Genetics Variations
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Binary fission in prokaryotic cell
Replication of bacterialchromosome
Asexual reproduction
offspring genetically
identical to parent
where does variation
come from?
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Genetic Variation : in bacteria
Sources of variation spontaneous mutation
transformation
plasmids DNA fragments
transduction
conjugation
transposon
bacteria shedding DNA
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Spontaneous mutation
Spontaneous mutation is asignificant source of variation
in rapidly reproducing species
Example: E. coli
human colon (large intestines)
2 x 1010 (billion) new E. colieach day!
spontaneous mutations
for 1 gene, only ~1 mutation in 10 million replications each day, ~2,000 bacteria develop mutation in that gene
but consider all 4300 genes, then:
4300 x 2000 = 9 million mutations per day per human
host!
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Transformation
Bacteria are opportunists pick up naked foreign DNA wherever it
may be hanging out
have surface transport proteins that arespecialized for the uptake of naked DNA
import bits of chromosomes from other
bacteria
incorporate the DNA bits into their ownchromosome
express new gene
form of recombination
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Conjugation
Direct transfer of DNA between 2 bacterial cellsthat are temporarily joined results from presence of F plasmid with F factor
F for fertility DNA
E. coli male extends sex pilli, attaches to femalebacterium
cytoplasmic bridge allows transfer of DNA
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Transduction
Phage viruses carry
bacterial genes from one
host to another
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Transposons
Insertion oftransposon
sequence in new
position in genomeInsertion sequences
cause mutations
when they happen to
land within the codingsequence of a gene or
within a DNA region
that regulates gene
expression
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Genetic variation : in human
Genetic variability in sexual reproduction independent assortment
homologous chromosomes in meiosis 1
crossing over between homologous chromosomes in prophase 1
random fertilization
random ovum fertilized by a random sperm
metaphase1
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Independent assortment
Meiosis introduces genetic variation gametes of offspring do not have same genes
as gametes from parents
genetic recombination random assortment in humans produces 223
(8,388,608) different combinations
from Mom from Dad new gametesmade by offspring
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Crossing over
During prophase 1 homologous pairs swap
pieces of chromosome
sister chromatids intertwine crossing over
tetrad
synapsis
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Meiosis & Crossing over
Meiosis & crossing over introduce greatgenetic variation to population
drives evolution
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Sexual reproduction creates variability
Sexual reproduction allows us to maintain bothgenetic similarity & differences.
Martin & Charlie Sheen, Emilio Estevez
Michael & Kirk
Douglas
Baldwin brothers
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The end
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