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Description
Flashcards by Matthew Orr, updated more than 1 year ago
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Created by Matthew Orr
over 6 years ago
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| Question | Answer |
| Mutations - Basics | - Changes in DNA (or RNA) of a cell (or virus) - Some inherited, not all - Essential for evolution - ~200 de novo (new) mutations per human child - ~20 billion new mutations per year |
| Mutations - Origins | - Errors in replication - Damage to DNA - Inheritance in germ line - Not passed on in somatic cells, so they are a genetic dead end - UV radiation causes Thymine dimers, which can lead to frame shift mutations |
| Mutations - Consequences | - Most affect unimportant regions of DNA, such as areas between genes - Most are silent (have no noticeable effect) - Consequences are dependent on mutation type and position - Effect on an organism or population dependent on if the mutation is dominant or recessive |
| Recessive Mutations - Examples (Albinism) | - Albinism --Body cannot convert tyrosine to melanin -- Leads to lack of skin and hair pigmentation |
| Mutations - Recessive or Dominant | 4 Rules of Thumb -1- Think from point of view of the mutant allele (e.g. mutant is recessive to wild type, NOT wild type is dominant to mutant) -2- Remember that genes make gene products, which are what affect phenotype -3- MOST recessive mutations are loss-of-function mutations, and MOST loss-of-function mutations are recessive (complete loss-of-function = null allele) -4- MOST dominant mutations are gain-of-function and MOST gain-of-function mutations are dominant -Most mutations (~95%) are recessive, as it is easier to damage something than make it work differently or better |
| Dominant Mutations - Importance | - Evolution: dominance effects how a mutation behaves in a population - Gene therapy strategy: how to treat mutations - Informs biology: e.g. wingless mutant flies: does the normal gene product make or prevent a wing (recessive wingless mutation = normal product makes a wing, dominant wingless mutation = normal product prevents a wing) |
| Dominant Mutations - Gain of Function | Gain of function can mean: - more than a normal function - a whole new function |
| Dominant Mutations - Examples (Achondroplasia) | - Achondroplasia -- Mutation in FGFR3 receptor -- FGFR3 slows limb growth when activating receptor -- Achondroplasia "locks" receptor on, causing massive reduction in limb growth -- Only ~20% of those with achondroplasia have a parent who also has it |
| Recessive Mutations - Examples (PKU) | - PKU (Phenylketonuria) -- Body cannot convert phenylalanine to tyrosine -- Leads to build up of phenylpyruvic acid, which causes progressive brain disfunction |
| Dominant Mutations - Examples (Huntington's Disease) | - Huntington's Disease -- Progressive neurodegeneration -- Carriers (heterozygotes) have the phenotype, so is a dominant autosomal mutation -- Mutation increases length of polyglutamine tract on the end of the Huntingtin protein, making the protein a neurotoxin -- It is a dominant, lethal mutation, which is rare |
| Genomes - Basics | - Genome sequence consists of genes (37.1% of genome) and intergenic DNA (62.9% of genome) - Human genome is ~3 billion base pairs, but is diploid so ~6 billion base pairs - Humans have ~20,441 protein coding genes, compare to the ~35,679 protein coding genes in rice |
| Genomes - Types of Genes | - Homologs: genes shared by different species, originally from a common ancestor - Orthologs: genes evolved from common ancestral gene, retain the same function in the course of evolution - Paralogs: genes related by duplication within a genome, evolve new divergent functions |
| Mutations - Types (INDELS) | - INDELS -- Insertions/Deletions -- Can be very small (1bp, 2bp) -- Can affect protein product of a gene -- Can affect function of non-coding RNA |
| Mutations - Types (CNVs) | - CNVs -- Copy Number Variants -- Variations in the number of repeats of a segment of DNA in a chromosome -- Typically 500bp to 1 million bp segments -- Account for most of the variation between the genomes of individuals of the same species |
| Mutations - Types (Point Mutations/Variants) | - Point Mutations/Variants -- best understood and easiest to study -- some are private (~200 de novo mutations per human), some are fairly common (<1% of alleles in a population, called "variants"), and some are very common (>1% of alleles, called "polymorphisms") |
| Mutations - Types (SNPs) | - SNPs -- Single Nucleotide Polymorphisms -- Some are rare (between 1% and 4.9% allele frequency), and some are common (5% or greater allele frequency) -- Can affect the protein product of a gene -- Can affect function of non-coding RNA if they occur there -- Can affect regulatory regions of the genome -- MOST are silent -- A common SNP occurs approximately every 1000 base pairs in human genome, so humans have 3 million common SNP loci |
| Allele Frequency | - Allele frequency (allele A) = (no. of A)/total - Express allele frequencies as decimals |
| Hardy-Weinberg Equilibrium | - Hardy-Weinberg equilibrium predicts that allele and genotype frequencies in a population remain constant from one generation to the next - For a given pair of allele frequencies, p and q the equation is p^2 + 2pq + q^2 = 1 - Most SNPs are in Hardy-Weinberg equilibrium - But some are not, possibly due to: non-random mating (e.g. inbreeding), the population is not homogeneous, the population is (or recently was) very small, and natural selection |
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