Plasticity Flashcards
where do new ALLELES come from
mutations
what kinds of mutations can create new alleles
- alterations to DNA that escape repair BEFORE replication
- copying error DURING rplication
do mutations always cause a visible change to a phenotype?
- no
- sometimes they may be in a noncoding region that does not affect the amino acid produced
explain DNA repair
mutations a common but most are repaired by mismatch repair enzymes and proofreading enzymes
how does a mutation in the DNA affect the amino acid
- point mutations
- indels
mutation in the DNA - point mutation
- the substitution of one base for another
- can be silent, nonsynonymous (missense), or nonsense
point mutation - silent mutation
- no change in the amino acid
- produces a normal protein
point mutation - nonsynonymous mutation
- change in the amino acid
- produces an abnormal protein
point mutation - nonsense mutation
- premature stop codon
- produces an incomplete, nonfunctional protein
mutation in the DNA - indels
- insertion (mutation in introns)
- deletions (mutation in exons)
- both results in a large scale frame shift
indels - large scale frame shifts
- shifts amino acids downstream
- results in new amino acid sequence
- resulting protein is unlikely to have any biological activity
what type of mutation should matter most for evolution?
- nonsynonymous
- the changes would be really subtle and could lead to a new function
explain the rates of mutations
- they vary greatly from species to species
- each human has about 36 point mutations per parent (~70 mutations per individual)
- mutation rates can evolve
where do new GENES come from?
- gene duplication
- new genes from scratch (some are born from noncoding DNA)
new genes - gene duplication
- should not affect phenotype
- its neutral but has the potential to create diversity and it may not be advantageous
- can happen via: unequal crossing over and retroposition or retroduplication
gene duplication - what happens in normal crossing over
- recombination
- occurs in prophase in meiosis I
- creates chromosomes with new combination alleles
- generates diversity
gene duplication - unequal crossing over
it is an error in the genetic recombination that happens during meiosis resulting in gene duplication
gene duplication - retroposition/retroduplication
- a processed mRNA (with the introns already spliced out) is reverse-transcribed by the enzyme reverse transcriptase to form DNA
- if this DNA integrates into one of the main chromosomes, the genome acquires a duplicated copy of the original gene
why is gene duplication important for evolution
- allows mutation to occur in a new gene while still retaining the original function
- gene duplication followed by divergence results in a new functional gene
- more of the genome is affected by copy number variation than point mutations
chromosome mutations
- inversions
- whole genome duplication
chromosome mutations - inversions
results when a chromosome segment breaks in two places and reanneals with the integral segment reversed
chromosome mutations - why do inversions matter
- breaks up linkage groups
- breaks new linkage groups
- creates supergenes which allows selection to act on groups of alleles
chromosome mutations - whole genome duplication
- if homologous chromosomes fail to segregate during meiosis I or if sister chromatids do not separate properly during meiosis II
- resulting cells may have double the number pf chromosomes of the parent cell
whole genome duplication - what is polyploid
organisms with more than two chromosome sets
generally explain the process of whole genome duplication
- starts with 2n, then mutates to become 4n
- self-fertilization creates another 4n in the second generation
why is whole genome duplication important for evolution and speciation
- the diploid parent cannot reproduce with the tetraploid offspring
- results in reproductive isolation and speciation
how do mutations affect fitness
- mutations can be lethal, deleterious, neutral, or beneficial
- lethal and deleterious outnumber neutral and beneficial
how do mutations affect fitness - what would happen if there was no selection
organisms will die bc selection takes out deleterious mutations
explain the mutation-selection balance
selection balances mutations which can be a majority deleterious
