Genetics and Evolution
- Created by: jessica
- Created on: 15-04-13 12:20
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- Genetics and Evolution
- Inversions
- segment of chromosome is cut out, flipped and reinserted
- two types of inversion, paracentric and pericentric
- paracentric is when the centromere is outside the inversion
- can lead to deletion products
- pericentric when the inversion spans the centromere
- can lead to duplication
- paracentric is when the centromere is outside the inversion
- INhertied diseases
- often due to recessive alleles as they can create reservoirs
- e.g. huntington's chorea is autosomal dominant
- e.g. fibrocystic disease is an autosomal recessive gene
- Variation at chromosomal level
- polymorphism for chromosome number and morphology includes extra chromosomes, reciprocal translocations, inversions
- Mendel
- his conclusions were that characters are controlled by pairs of alleles which can be dominant or recessive. alleles segregate at random
- created law of independent assortment and law of segregation
- Complementation
- production of wildtype phenotype when two haploid genomes bearing different recessive mutations are united in the same cell
- Complementation test
- intercrossing two homozygous individiuals for different recessive mutations, observing whether the progeny have wild type phenotype
- complementation group when two or more groups control a phenotype
- used to classify mutations as alleles of the same or of different genes
- Sex linked inheritance
- Morgan found white eyed male flies amongst a red eyed fly population
- examples of human sex linked inheritance are haemophilia, DMD
- X linked recessive disorders are when males show the phenotype
- X linked dominant disorders also occur
- The nature of variation
- complex gene traits
- phenotype can be expressed in one of 3 ways, continuous, meristic and threshold
- continuous
- polygenic plus environmental determination, no discrete classes of phenotype, no discontinuities
- meristic
- polygenic plus environmental determination, underlying distribution is continuous, phenotype only expressed in whole units
- threshold
- polygenic and environmental distribution with few phenotypes, have underlying predisposition for the trait
- continuous
- phenotype can be expressed in one of 3 ways, continuous, meristic and threshold
- complex gene traits
- Pedigree patterns
- used to track inheritance in humands and livestock
- four main patterns of inheritance are autosomal dominant, autosomal recessive, X lionked recessive, Y linked dominant
- autosomal recessive disorders appear in progeny of unaffected parents and the affected progeny are both male and female
- autosomal dominant disorders have phenotypes that appear in every generation of the pedigree and there is equal representation of both sexes
- Linkage and recombination
- recombination when homologous chromosomes can exchange sections
- big physical distance means more likely to cross over
- crossing over occurs at prophase 1 of meiosis
- multiple cross overs occur with map distance greater than 10cM
- recombination when homologous chromosomes can exchange sections
- gene interactions
- interactions between alleles within a single gene include complete dominance, incomplete dominance co-dominance
- complete dominance is the base default Mendelan setting
- incomplete dominance is when the the heterozygous phenotype is intermediate to the two parent phenotypes and the parents are homozygous
- codominance is when the heterozygote displays the phenotype of both homozygotes
- epistasis is interactions between genes
- phenotypic effects arise when 2 or more genes interact and genes are no longer independent of each other
- changes F2 phenotypic ratios, will be less than 4 phenotypes
- penetrance and expressivity are interactions between genes and the environment
- penetrance is the proportion of individuals carrying a particular allele that expresses the associated phenotype
- expressivity measures the extent to which a genotype exhbitis its phenotype
- interactions between alleles within a single gene include complete dominance, incomplete dominance co-dominance
- genetic mapping
- relies on DNA polymorphisms rather than "real" genes
- uses various DNA polymorphisms including RFLP, VNTR, STR, SNP
- protein polymorphisms
- different types of protein polymorphisms, immunologic and amino acid sequence
- immunologic polymorphism when the 40 different specificities for antigens on human red blood cells
- amino acid polymorphism is when amino acid substitutions may directly replace a charged or noncharged substitution near a charged amino acid
- Phenotypic variance is determined by genes and environment
- Vp=Vg + Ve
- Vg valculated by Va + Vd
- Va=additive variance, Vd=dominance variance
- The 2 alleles can have dominance interactions and either allele can show dominance
- additive variance when each allele in a polygenic system contributes to the observed phenotype
- positive additive will increase the strength of the phenotype
- negative additive will decrease the strength of the phenotype
- Va=additive variance, Vd=dominance variance
- Vg valculated by Va + Vd
- Vp=Vg + Ve
- Heritability
- measure of the influence that genes have on a phenotype
- allows the measure of contribution of genetic components
- 2 types of heritability broad and narrow
- equation for broad heritability is H2 = Vg/Vp
- equation for narrow is h2=Va/Vp
- narrow is more specific
- is the property of variation within one population in one environment at one time, are ratios
- Hardy-Weinberg equilibrium
- sexual reproduction does not cause a constant reduction in genetic variation in each generation, so amount of variation remains constant in the absence of other driving forces
- uses the assumption that mating is random and there are no selection pressures
- equation is p+q=1 and p2+2pq+q2=1
- p is the dominant allele and q is the recessive allele
- genetic structure of populations
- population genetics applies to the genetic principles to entire populations of organisms
- aubpopulation is a population unit within a larger population
- Mendelian population is the natural interbreeding unit of sexually reproducing plants or animals sharing a common gene pool
- gene pool is all the alleles in a population
- genotype frequency is the proportion of individuals in a population with a specific genotype
- allele frequency is when the proportion of each specific allele in a population
- allele and genotype frequencies remain the same if there is random mating, no mutation, mo migration, no selection, no random genetic drift
- genotype frequency is the proportion of individuals in a population with a specific genotype
- allele and genotype frequencies remain the same if there is random mating, no mutation, mo migration, no selection, no random genetic drift
- Inbreeding and genetic burden
- inbreeding when there is a higher than chance related mating
- combines alleles of common ancestory, promotes homozygosity
- effects are more pronounced in small isolated populations
- promotes the incidence of genetic abnormalities
- outbreeding when there is lower than chance related mating
- assortative mating is when there are more traits in common
- disassortative mating is when more of the traits are dissimilar
- inbreeding when there is a higher than chance related mating
- Forces of evolutionary change
- mutation
- raw material of evolution, genes and chromosomes mutate
- chromosome mutations are deletions, translocations, nondisjunction and inversions
- gene mutations are point, substitutions, inversions/deletions and frame shift
- raw material of evolution, genes and chromosomes mutate
- selection
- directional, diversifying, stabilizing
- diversifying can lead to speciation
- most likely cause of rapid changes in allele frequency
- selective advantage depends on relative fitness of genotypes
- directional, diversifying, stabilizing
- migration
- movement of alleles between populations
- genetic drift
- chance fluctuations in allele fequency due to random sampling of gametes
- mutation
- Neutral mutations and molceular evolution
- mutations can have three effects on fitness-deleterious, increase, neutral
- neutral has no effect on fitness
- rate of neutral replacement = 2Nu x 1/(2N) = u
- mutations can have three effects on fitness-deleterious, increase, neutral
- Speciation
- new species defined when it can no longer mate with its former self
- Allopatric speciation when physical isolation is involved
- Sympatric speciation is when populations are reproductively isolated but may not be physically isolated
- pre mating isolation mechanisms include ecological, seasonal/temporal, sexual, mechanical, isolation by different populations
- postmating isolation mechanisms include gametic isolation, hybrid unviability, hybrid sterility, hybrid breakdown
- Phylogeny and Systematics
- phlogeny is a branching diagram showing relationships between species based on their shared common ancestor
- cladogenesis is the splitting of evolutionary linkages to form clades
- anagenesis is the accumulation of phenotypic changes within a lineage
- synapomorphies are traits mapped onto a phylogenetic map
- monophlyetic group includes an ancestor and all of its descendants
- paraphyletic group includes an ancestor and some but not all of its descendants
- polyphyletic group includes two convergent descendants but dont shar a common ancestor
- convergence is the acquisition of the same biological trait in different lineages
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- Inversions
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