Genome Seq and Evolution, Cluster and Repeats Flashcards
Polymorphism
Existence of 2 or more variants
Alleles on a gene show extensive polymorphism at sequence level, but…
Many sequence changes do not affect function
Responsible for most of genetic variation between individuals?
SNPs
A change in DNA sequence in a coding region that does NOT alter the amino acid encoded (faster accumulation than opposite)
Synonymous mutation
A change in DNA sequence in a coding region that alters the amino acid encoded
Nonsynonymous mutation
Frequency of a neutral mutation depends on…
Genetic drift
Gene conversion bias
Increases GC content
Mutational bias
High AT content (methylation of amine)
Fixation
Process by which a new allele replaces the allele that was previously predominant in a population
Small population vs large population fixation opportunity?
Small population = higher fixation opportunity
Genetic hitchhiking
Change in frequency of a genetic variant due to its linkage to selected variant at another locus
NS > S Substitutions
Positive selection
S > NS Substitutions
Negative selection
Nonrandom association between alleles at two different loci
Linkage disequilibrium
______ substitutions accumulate 10x faster than ______ substitutions
Synonymous, nonsynonymous
How is evolutionary divergence between DNA sequences measured?
Corrected % of positions at which corresponding nucleotides differ
Genes that are unique to vertebrates are connected with…
Immune and nervous systems
Duplicated genes can ______, or one copy can _______
Diverge to generate different genes, become an inactive pseudogene
Globin gene clusters
Arose by duplication and divergence from ancestral gene that had 3 exons (alpha and beta-globin separated in early vertebrate evolution period)
Processed pseudogenes result from…
Reverse transcription and integration of mRNA transcripts
Nonprocessed pseudogenes result from…
Incomplete duplication or second-copy mutation from functional genes
Increases the chromosome number by a multiple of two (gene duplication)
Polyploidization
Polyploidization from mitotic or meiotic errors within a species
Autopolyploidy
Polyploidization from hybridization between two different but reproductively compatible species
Allopolyploidy
2R Hypothesis
Early vertebrate genome underwent two rounds of duplication
Mispairing between nonallelic loci can…
Cause unequal crossing-over
rDNA cluster organization
Transcription units alternate with nontranscribed spacers
Nontranscribed spacers
Short repeating units whose number varies so lengths vary
Ribosomal RNA (rRNA) encoded by…
Large number of identical genes that are tandemly repeated to form one or more clusters
Concerted evolution
Explains why paralogous genes within one species are more closely related to each other than members of same gene family in another species
