* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Document
Artificial gene synthesis wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Behavioural genetics wikipedia , lookup
Heritability of IQ wikipedia , lookup
Quantitative trait locus wikipedia , lookup
Genetic studies on Bulgarians wikipedia , lookup
Genetics and archaeogenetics of South Asia wikipedia , lookup
Medical genetics wikipedia , lookup
Pharmacogenomics wikipedia , lookup
Gene expression programming wikipedia , lookup
Koinophilia wikipedia , lookup
Designer baby wikipedia , lookup
Genetic testing wikipedia , lookup
History of genetic engineering wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Public health genomics wikipedia , lookup
Genetic engineering wikipedia , lookup
Genome (book) wikipedia , lookup
Inbreeding avoidance wikipedia , lookup
Human genetic variation wikipedia , lookup
Hardy–Weinberg principle wikipedia , lookup
Genetic drift wikipedia , lookup
Individual fitness is the reproductive success over an individual life cycle, with respect to other members of a population. Fitness of a zygote depends on the probability of survival to reproductive age, number of gametes contributing to the production of descendant, and the number of descendant which succeed in passing their own genes to the next generation; There is a positive correlation between fitness and level of heterozygosity It is generally not easy to measure overall fitness. Fitness components are easier to quantify. These are generally characteristics linked to physiology, metabolism, survival and reproduction of an organism. Grey wolves from Isle Royale Population established in 1949 Ht / H0 = 0.039 / 0.087 = 0.45 Reduced reproductive output Reduced survial of pups Inbreeding depression N 40 15 ♀♂ Low levels of genetic diversity at both functional and selectively neutral loci Adder (Vipera berus) Reduction in clutch size Abnormalities in youngsters 1 Florida panther N 60 – 70 Low variability recorded at nucelar loci and mitochondrial DNA sequences with respected to other populations and other big cats Asiatic lion Gir Serengeti Ngorongoro Panthera leo persica Panthera leo azandica and nubica Individual fitness reduction • 41 nuclear loci • mtDNA • DNA fingerprints (multilocus, minisatellites) Mantle hair loss (higher susceptibility to patogens) Tail malformation Heart defects (atrial septal defects) Cryptorchidism (undescended testicle) Low semen production Defect in the head and tail of the spermatozoon 2 Cheetah • 52 nuclear loci • mtDNA • Major histocompatibility complex (MHC) • DNA fingerprints (singlelocus, microsatellites) • Acceptance of allogenic skin grafts from unrelated individuals High susceptibility to infections (felin infectious peritonitis) Abnormal sperm morphology High natal mortality (30%) Highest fitness occurs when expression of recessive, deleterious alleles is masked by dominant alleles; This is the dominance hypothesis used to explain reduction in fertility, progeny body mass, growth and survival rate, and higher patogen susceptibility recorded in populations with high inbreeding coefficients; According to the dominance hypothesis, inbreeding increases the probability that recessive deleterious alleles are found in homozygote state and can therefore be expressed. Purging selection Recessive lethal or deleterious alleles become evident through inbreeding, and can therefore be eliminated (purged) via natural selection; 3 Aldabra giant tortoise Colonization: 80,000 years before present Single mitochondrial line Low allelic variability at eight microsatellite loci N = 100,000 N California elephant seal 20 – 30 (probably just one harem left) N 100,000 Reduced genetic variability at 20 loci Two mitochondrial lines In small, non isolated populations allelic frequencies vary because of the interaction of migration and genetic drift; Genetic drift results in a decrease of genetic variability of a population and an increase of genetic differentiation among populations; Gene flow, on the other hand, leads to an increase of genetic diversity and to a homogeneization of allele frequencies among populations. 4 After t generations, an equilibrium is reached whereby the number of alleles lost to genetic drift is counter‐balanced by the alleles gained from migrants; The probability of autozygosity expressed by the coefficeint of inbreeding will have a different value when, from one generation to the next, allele frequencies change because of gene flow among populations. When the number of alleles lost to genetic drift equals the number of alleles gained from migrants, Fe denotes a relation of dynamic equilibrium between genetic drift and gene flow Fe = 1 1 + 4Nem • In a small population, gene flow will have to be relatively higher to counteract genetic drift than in larger populations • The inbreeding coefficient decreases very fast with respect to single increment of gene flow. A small number of migrants can result in a drastic inbreeding (F) decrease. 1 0.8 Nm = 0.25 (one migrant every 4 generations) Fe = 0.50 Nm = 1 Fe = 0.20 0.6 Fe 0.4 1 Fe = 1 + 4Nem 0.2 0 0 1 2 3 4 5 6 7 8 9 10 Number of migrants per generation (Nem) 5 Fitness rebound Introduction of individuals from nearby populations results in fitness increase) Adder (Vipera berus) Florida panther (Puma concolor coryi) N 60 – 70 Fitness rebound thanks to translocation of invididuals Puma concolor coguar from central North America Factors affecting population genetic structure • Population (small) size and genetic drift • Population structure • Mating system (deviation from random mating) • Mutation • Migration (gene flow) • Selection - different gamete fertility different survival of zygotes 6 Allelic frequencies p and q, for alleles A and a, respectively, under HWE: p (A) q (a) AA Aa p+q=1 p (A) q (a) p pq 2 aA aa qp q 2 Expected genotipic frequencies: AA: p Aa: 2p q 2 AA aa: q 2 aa A random sample of the population results in equal allele frequencies (0.5). The actual population structure is unknown and the expected genotype frequencies under Hardy-Weinberg equilibrium will be: p2 = 0.25 q2 = 0.25 2pq = 0.5 The actual genotype frequencies are p2 = 0.5 q2 = 0.5 2pq = 0 There is a deficit of overall heterozygotes even with random mating in each deme. This is due to the absence of gene flow between demes. AA aa Genotype frequencies reach equilibrium when the barrier is eliminated and a panmictic regime is established in the population (isolate breaking or Wahlund effect) Genotype frequencies change from ½ AA, 0 Aa, ½ aa to ¼ AA, ½ Aa, ¼ aa The frequency of homozygotes decreases from 1 to ¼ + ¼ = ½. 7 hn h3 h1 h2 HS - HO FIS = HS h1 h2 HS1 FST = FST = HS2 HT - HS HT HT - HS HT FST is the reduction in heterozygotes in the average subpopulation with respect to the total, panmictic population; That is the probability of two alleles of a subpopulation being identical by descent (IBD) with respect to the probability of two alleles drawn from the entire set of subpopulations (the total population) being IBD; FST is a measure of the level of genetic differentiation among (sub)populations. 8 p q HE (2pq) Population A1A1 A1A2 A2A2 1 0.25 0.50 0.25 0.5 0.5 0.5 2 0.04 0.32 0.64 0.2 0.8 0.32 HS = 0.41 0.35 0.65 p HT = 0.455 q m x HT = 1 - 2 i i =1 h1 h2 HS1 FST = HS2 HT - HS HT HS3 HS1 FST = HS2 HT - HS HT 9 HS3 HS1 FST = HS2 HT - HS HT An example of population divergence estimated by , using the software Arlequin 10 Results are shown in the default browser in html format Compare FST values and check for statistical significance 11 Galàpagos giant tortoises Pinta ISABELA Marchena Santiago Fernandina Genovesa Pinzón St Cruz St Cristóbal St Fé Española Floreana St. Salvador St Cruz Pinzon St Cristobal Sierra Negra Cerro Azul Isabela Espanola 12 ISABELA V. ALCEDO SIERRA NEGRA CERRO AZUL EAST WEST CABO ROSA Volcano CR 20 km LP LT LC PEG ISABELA Sierra Negra (CR) – Cerro Azul (W) LP 0.303 – LT 0.205 0.002 – LC 0.173 0.191 0.229 PEG 0.957 0.846 0.747 Cerro Azul (E) – 0.004 – Genetic distances between tortoise popolations of volcan Cerro Azul and Sierra Negra based on FST values 13