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Lecture 12

Lecture 12 - 16 - EVOLUTION SECTION

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Biology 1001A
Beth Mac Dougall- Shackleton

Lecture 12 Co Dominance– When both alleles in a heterozygous individuals are shown in its phenotype. For example RW sows red and white colors on a flower Alleles have equal effects on the individual. Incomplete dominance – When an intermediate allele is shown. Ie// RW shows pink color on flower. Pleiotropic: When one single gene affects more than one other effect on the body phenotypically. Example, sickle cell disease can cause heart failure and also fatigue and impaired mental function. So one allele has an effect on many other processes. H ARDY W EINBERG E QUILIBRIUM Hard Weinberg equilibrium is when genetic variation in a population will remain constant from one generation to the next when there is no factors that disturb it. 5 CONDITIONS… 1. No mutations occur 2. No migration 3. Very large population size 4. All genotypes survive and reproduce equally as well 5. Random mating This is point of genetic equilibrium: this is when no change in allele or genotype frequencies are occurring in succeeding generations. This is a null model and a reference point for evaluating circumstance in which evolution can occur. Protein Production DNA in nucleus, alleles gets transcribed into RNA and leaves nucleus. Goes to ribosomes and go to ER. They get translated on ER (RNA to protein) and packaged into vesicles. Go to Golgi apparatus. Then the proteins are sent from vesicles to the membrane. Pigment Production Melanin (black and red melanin). Melanin is produced by melanocytes. It is packed into melanosomes. They export the melanin to keratinocytes, which give hair and skin their colors. Brown is a mixture of red and black melanin. GENE PRODUCT is W-MC1R (brown allele) which sits in the membrane (membrane product). It AMP levels are high, it makes black melanin. In hormone response, when AMP levels are low, RED melanin is produced. The B allele code for MC1R is always high (AMP levels always high is on all the time). The black allele is always on so it is DOMINANT. The dominant alleles never inhibits the recessive one, the allele that is on all the time is the dominant and it is determining the phenotype. In a population with no fitness, the starting allele frequencies will be maintained, doesn’t matter what is dominant and what is isn’t (WHE) Punnet Square for POPULATIONs Top and left are percentages. Lecture 13 Allele Frequencies: frequency of individual alleles Gene pool: all alleles of individuals in a single population Population: a group of sexually interbreeding individuals Deme: a local group of sexually interbreeding individuals in which gene pool is distinct. There an be many demes within ONE population of species. Once we know allele frequency in population (through HWE), then we plug values of p and q values into HW equation. If the value is 1, then these are the expected ratios. Selection: not all genotypes have equal fitness. Some genotypes may be more likely to produce phenotypes that cause the pigs to be eaten. These have low fitness. Average Absolute fitness (W); for example 8 offspring per lifetime Average Relative Fitness (w): relative to other genotypes, how better is this fitness. Is it average and higher than average. (w). Most important one.  Fittest genotype has a w=1, so all others are w=W/W max  When selection is happening, we have to know the dominance of alleles. Dominant (favourable) will never outcompete recessive.  If we have a beneficial recessive allele, it will take a long time to get established. The recessive can OUTCOMPETE dominant deleterious allele over time. Lecture 14 Batesian Mimicry: A palatable species (one that can be eaten) mimics another member of the same species that is not palatable. It mimics the dangerous warning code that predators are scared of. Mullerian Mimicry: 2 unrelated species that are BOTH dangerous, mimic the same warning code even though they are completely different from each other. Genetic Load: extent to which population moves away from optimal genetic constitution. Different Types of Selection: Selection of single locus Most traits are not governed by a single locus, they are more continuous distribution. Stabilizing Selection: intermediate have much better fitness. Ie// medium sized birds have highest fitness Directional: selection in favour of extreme phenotypes ie// large birds are most favoured and selected. Not all populations experience directional in the SAME direction. They can vary over time. Disruptive Selection: Individuals at both extremes are selectively favoured so they have the highest fitness. Frequency – Dependent Selection ( the fitness of geneotypes relies on frequency of it) NEGATIVE FREQUENCY DEPENDENCE (being rare)  Advantage of being rare  Ie// predators who form search images of prey. If there is a lot of grey squirrels, then hawks form a search image of grey squirrels. So the rare squirrel (white squirrel) will be most fit. POSITIVE FREQUENCY DEPENDENCE (BEING COMMON)  When predators learn which warning to avoid. Warning coloration for example. This lets the predator know its better to avoid eating the individual. Why aren’t all living things perfectly adapted to their environment?\  Environment is always changing and natural selection cant predict future  Selection doesn’t always choose the best alleles, what if these alleles aren’t even present  Limited by dominance relationships  TRADE OFF ; good in one reason but negative effect for another reason NONADAPTIVE EVOLUTION: Genetic Drift: random unpredictable changes in allele frequencies. Not selection. Very strong in small populations They can oppose selection. If selection is trying to get a deleterious allele out, genetic drift can bring it back.  How does drift affect variation within a population: decrease, causes one allele go to fixation. Mutation: mutation is not directed towards the need of the organism.  Most mutations have neutral effects of fitness, but the ones that due affect fitness are harmful. Most mutations oppose selection, but some may be material for adaptation. Gene Flow (migration): movement of alleles between populations.  Can introduce new alleles  Can oppose selection (selection-migration balance) – prevents population from being perfectly adapted to the environment. Ie// a black rat living in black mountain moves to white mountain with white rats. Ruins fitness of the white rats. Hardy- Weinberg assumes random mating - But mating
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