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BIOL10004 Quiz: Genetic diversity arises by mutation and recombination
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Biology
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BIOL10004
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Genetic diversity arises by mutation and recombination
Genetic diversity is caused by mutation and recombination
Mutation:
Radom chemical event causes mutation
- Replace a base by another
- Insertion / deletion of base
- Rearrangement of large region of chromosome
Not necessarily harmful or beneficial
Synonymous mutation:
- Change from one codon for an amino acid to another codon for the same amino acid
- Only a little effect on survival or reproduction of the carrier
Missense mutation:
- A mutation changes the nucleotide sequence of a condon, cause it encodes a
different amino acid
Lethal mutation:
Result in failure of the organism to survive during the development
- Kill the organism
Slightly detleterious mutation:
- Mutatio that do’t kill a ogais ut odeatel edue its fitess
Alleles that arise from advantageous mutations increase in frequency only because they
cause greater fitness to individuals in a given environment.
Only synonymous mutations or very rare advantageous mutations would produce alleles
that increase in frequency in the population.
Recombination
is a process by which pieces of DNA are broken and recombined to produce new
combinations of alleles.
In eukaryotic cell,
- Recombination occurs during meiosis
- During the first phase of meiosis, the homologous pairs of maternal and paternal
chromosomes align.
- During the alignment, the arms of the chromosomes can overlap and temporarily
fuse, causing a crossover
- Crossovers result in recombination and the exchange of genetic material between
the maternal and paternal chromosomes
recombination rapidly generates new allele combination, then generate new genetic
variants ( genotype )
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Recombination is limited in some species that are haploid, cos it can only happen when
two different genome are present in a diploid cell
Stability and change in genetic structure of population
Genetic composition of a population can be presented by a proportion of alleles and
genotype in that population
Allele can increase or decrease in frequency in a population
Random mating :
- Each individual has an equal chance of mating with each other individual
- Alleles of each locus are paired up at random to make new genotypes in each
generation
HardyWeinberg principle
- a model for the genetic structure of a population
- states that phenotypic proportions in an ideal population
- tend to remain constant at equilibrium values that can be estimated from allele
proportions.
- 5 properties:
1. no mutation
2. population is infinitely large
3. individuals mate at random
4. no exchange of genetic material with other population ( gene flow)
5. no natural selection
- Hardy-Weinberg equilibrium:
The equation p2 +2pq+q2= 1 predicts an equilibrium
p + q =1
- e.g. a population contain single polymorphic locus with two alleles, A and a.
# population will contain three genotypes ( AA, Aa, aa)
# If the proportion of A allele in population is p, proportion of a allele is q
# after one generation an ideal population will establish an equilibrium
*which proportion of AA=p 2 , Aa=2pq and proportion of
aa = q2
Evolutionary change may result if there are deviations from the HardyWeinberg
equilibrium.
Deviation from the Hardy-Weinberg equilibrium
Mutation is a week evolutionary force:
- Is a deviation from the Hardy-Weinberg ideal population
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- mutation is essential for the initial generation of genetic variation, its low frequency
of occurrence makes it unlikely to significantly shift a population from the Hardy
Weinberg equilibrium.
Gene flow
- The exchange of genetic material between population
- can affect the proportions of alleles if the populations have different alleles, or the
same alleles with different proportions.
- The greater the different on allele proportion between the gene pools, the greater
effect will be
- where gene flow is low, populations are free to diverge genetically from one another
due to evolutionary forces
Assortative mating
- Non-random mating in which phenotypically alike (positive assortative mating )/
non-alike individuals mate preferentially (negative assortative mating )
- Natural population often exhibit assortative mating
- Positive assortative mating:
the two parents will often contribute the same allele to the offspring, so the
proportion of homozygotes will be higher than expected from random mating.
- Negative assortative mating:
when individuals prefer to mate with genetically dissimilar individuals.
Chance and inheritance: genetic drift
inheritance of alleles is a chance process, certain alleles may change in proportion from
generation to generation simply by chance.
Natural populations can undergo change because chance plays a role in inheritance.
Such a process is termed genetic drift.
The ado hage i a populatio’s allele feue fo oe geeatio to the et
that is attributable to chance, it occurs more quickly in small population
Genetic drift leads to a gradual loss of genetic variation in populations, as allele
frequencies drift to fixation
The tendency of small populations to lose alleles by genetic drift may account for the
high levels of homozygosity
Genetic drift is particularly important in small populations, for example, in small
founding populations (the founder event) or when populations decrease for a period of
time (a population bottleneck).
Founder event
Loss of genetic diversity when a small group of individuals separates from the larger
population and establishes a colony in a new location;
genetic drift is common due to the small population size
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Description
Genetic diversity arises by mutation and recombination Genetic diversity is caused by mutation and recombination Mutation: Radom chemical event causes mutation Replace a base by another Insertion deletion of base Rearrangement of large region of chromosome Not necessarily harmful or beneficial Synonymous mutation: Change from one codon for an amino acid to another codon for the same amino acid Only a little effect on survival or reproduction of the carrier Missense mutation: A mutation changes the nucleotide sequence of a condon, cause it encodes a different amino acid Lethal mutation: Result in failure of the organism to survive during the development Kill the organism Slightly detleterious mutation: Mutation that dont kill an organism but moderately reduce its fitness Alleles that arise from advantageous mutations increase in frequency only because they cause greater fitness to individuals in a given environment. Only synonymous mutations or very rare advantageous mutations would produce alleles that increase in frequency in the population. Recombination is a process by which pieces of DNA are broken and recombined to produce new combinations of alleles. In eukaryotic cell, Recombination occurs during meiosis During the first phase of meiosis, the homologous pairs of maternal and paternal chromosomes align. During the alignment, the arms of the chromosomes can overlap and temporarily fuse, causing a crossover Crossovers result in recombination and the exchange of genetic material between the maternal and paternal chromosomes recombination rapidly generates new allele combination, then generate new genetic variants ( genotype )
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