Lecture 5 Flashcards
Evolution requires
Variation
Polymorphism
Resulting in mimics by the species, occurs in areas of overlap
Evolution is impossible without
Variation
Genotype gives rise to
phenotype
Genotypic differences are partily responsible for
phenotypic differences
Phenotype can also be influenced by
Enviorment
Mutation is responsible for
differences in genotypes
Mutation gives us
Variation
Genome of all organisms consits of
DNA
DNA is
A serise of nucleotide base pairs
Base pairs are
a purine and a pyriminde
Purines are
Adenine and Gyanine
Pyrimidines are
Thymine and cytosine
DNA ladder
Phosphate is the backbone, base pairs are the rungs
DNA varation
Varys greatly amoung organisms, genome size doesnt corilate with complexity
Chromosome
One long DNA molecule coiled
Gene
Sequence of DNA that is transcribed into RNA
RNA is translated into
Protine
Locus
site on a chromosome occupied by a particular gene
Exons
Gene segments that code for a protine
Introns
Noncoding segments that occur between exons
Codon
3 basepairs of RNA, codes for specific protine
Amino acids
Building blocks of protines
How many possible codons and amino acids
64 codons, 20 amino acids, genetic code is redundant
3 codons are
stop codons
Alleles
Different forms of a gene
Alleles can code for
different phenotypes of the same trait like fur color
Alleles identified by
phenotype effect, but not all alleles have a phenotype effect
Haplotype
Particular DNA sequence that differers by one or more mutations from homologous sequence
Genetic markers
Detectable mutations that geneticits use to recognize specific regions of chromosomes or genes
Mutation
Alteration of a gene or chromosome and its product, DNA can be damaged by chemical and physical events
Mutations result in
change in base pair sequence, many changes are repaired by DNA polymerase
DNA polymerase
proof reading enzyme
Germline cell
Sex cells
Mutations only occur in
a single cell of a single organism
If mutation is in the germ line
it can give rise to a single gamete with that mutation, if its a precursor to germ line several gametes may carry the mutation
Initilly the mutation is
carried in very small proportion to population
Mutations can become
Fixed in the population due to natural selection or genetic drift
Fixed
carried by almost the whole population
fixed genes represent
the current wild type
most mutations do not
become fixed
Mutations must happen in —— to be passed on
germ line cells
Varriation arises from 2 sources
point mutations and sequencing changes arising from recombination
Point mutations are
single changes in DNA
sequence changes are
whole sequences of DNA changed all at one
Mutations can have a phenotypic effect if
the occur in genes that encode molecules involved in transcription/translation, regulatory DNA regions, and protein encoding regions
Recombination
shuffles existing, makes new allele combos
Base pair subsitutions
maps to a signle locus, offten restricted to a single base pair, can be transition or transversion
transition
A substitution of a purine for a purine G for A or a pyrimidine for a pyrimidine T for C, this is more likely than transversion
Transversion
a substitiution for a purine for a pyrimidine G for C
Synonymous mutations
Have no effect on the resulting amino acid, polypeptide, or protein
Nonsynonymous mutations
Result in amino acid substitution, codon changes substantially
DnDs ratio
Number of nonsynonymous mutations divided by number of synonymous mutations, can be used as indicator for natural selection
DnDs < 1
Most nonsynonymous mutations are deleterious and removed by purifying selection
DnDs= 1
Nonsynonomous and synonymous mutations are evolving largely neutrally
DnDs>1
many of the nonsynonomous differences between the species were fixed by positive selection
Frameshift mutation
insertion or deletion, resulting polypeptide is useually greatly altered, protine non functional
Insertion
a single base pair is inserted
deletion
a single base pair is deleted
Recombination
a normal process where genes are exchanged between chromosomes during meiosis
Unequal crossing over
When 2 chromosomes are not perfectly aligned, results in tandem duplication in one chromosome and deletion in the other, can range in size from single bp to whole segment
unequal crossing over usually occurs in
areas that already has tandem repeats, generate a large number of nonfunctional sequences, increases total length of dna
mutation is the ultimate sourse of
variation
another contribution to variation is
gene mixing through segregation and recombination durring meiosis, shuffles existing variation to create new gene combos
Non sexually reproducing organisms
horizontal gene transfer creates new gene combonations
without sources of variation
evolution wouldnt be possible
Effects on mutation are variable, depend on
where in the genome the mutation happens and the phenotypic trait that is affected
Pleiotrophy
multiple traits could also be effected
Rates of mutation are
difficult to measure due to mutations being synomyous and death or carriers
Rates will be different in
protein coding vs non protine coding regions
We used to rely on changes in phenotypes for rates of mutation
now we rely on DNA sequences
each human carrys around — mutations
70
mutation is a
random process, not all loci regions are equally mutable tho
The process of mutation is
stochastic rather then deterministic, we can determine probability of mutation occurring but we cannot predict which of a large number of gene copies will undergo mutation
Chance of a particular mutation will occur is not influenced by whether or not
the organism in an environment in which that mutation would be advantageous
Mutation rates may be elected by certain stressful environments but
environment cannot elect advantageous mutations
Karyotype
a description of the complement of chromosomes, includes number, size, shape, and internal arangement
Aneuploidy
unbalanced chromosome complement, usually results in inability or poor development
Polyploidy
changes in whole sets of chromosomes
diploid
organisms with 2 entire sets of chromosomes
polyploid
organism with more then 2 sets of chromosomes
Triploid zygots produce
aneuploid gamets, usually produce few offspring as result
Gametes of different ploidy levels may produce
different zygots that are 6N, 8N, ect
Polyploid may result in
instantaneous speciation, opens the possibility of multiple origins for a single species
