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Term / Study Topic Details Analysis
Diploidy Origin of sex One copy can be used as a template to repair When diploidy evolved, it must
Benefits of Diploidy ‘double-strand’ damage Bernstein 1985 have involved two identical sets
Back up copy to cover mutations of chromosomes.
Point mutation on strand can be repaired Expensive – more DNA to repair
J.M Mancebo-Quintana 2012-Origin of sex Why swap between
has 2 problems: need for a gamete to find diploid/haploid?
partner to merge with; cost in time and -Reduction division could
energy. 2: process of meiosis to return to evolved as response to changing
haploid state complex. environment.
-Expose recessive deleterious
mutations as haploid
Crossing Over Origins of sex Cutting and pasting between homologous Promotes variation- same factors
chromosomes happen at chiasma get that maintain sex
swapping of genetic material
Synagamy Origins of sex Restores heterozygosity Synagamy or crossing over first?
C.O: chromosomes identical so
no variation but good repair.
Synagamy: C.O between
homologous chromosomes
increase variation.
The two fold cost Costs of sex Mutation allows female to produce eggs by But no variation- susceptible to
model MITOSIS so are identical diploid copies of changes in environment and
herself and the male is redundant. Mutation disease
passes to 100% of her offspring (no 50:50
lottery of meiosis) all daughters can
reproduce asexually. Sex be half as efficient at
producing babies as asexuality, hence the
‘two-fold cost’.
Fisher Muller model Evolution of Sex - Sex By bringing good genes together. In asexual Only a benefit in large
Vicar of Bray model speeds evolution lineages beneficial mutation A prime spreads populations, and with mutations
Fisher 1930, Muller to fixation, but in different clone beneficial of small benefit (work by Crow) if
1932 mutation B prime. Only way to get both in small population then see trait
one individual is to occur in same clonal spread fast and if benefits from
lineage. mutation is large get fixation
With sex, beneficial mutations bought fast, so in small populations sex
together immediately. doesn’t speed things.
Mutation rare so chance 2
appears when 1 not fixed
depends on 1 not spreading
rapidly. Problem for theory
depending on how think
populations exist.
Sex speeds evolution only if
DIFFERENT individuals with
DIFFERENT beneficial mutations.
Goddard 2014-sexual species of
yeast gained beneficial
mutations and adapt better than
asexuals, but done in lab.
Muller’s Ratchet Evolution of sex – By bringing bad genes together in asexual Sex fights this as individuals with
model purges deleterious population – 0/1/2 deleterious mutations. 0 deleterious mutations can give
Herman Muller mutations die so ‘best’ on average have 1 mutation. So offspring with 0 mutations.
population has lower irreversible fitness so Restore perfect genome – dump
genetic drift. bad genes into same offspring
which dies. Group selection?
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