Unit 7

• Genetic drift is when one of the alleles are lost. This occurs in smaller populations. For example if 10% of 1000 individuals had that allele and reproduced successfully then that allele would pass on. If only out of 10 individuals had the alleles and failed to survive and have offspring then that allele is lost. Geneetic drift is important to create geneetic diversity.
• Gene flow is when one allele population goes to the other population. If another allele recieves this allele then the allele frequency will chage. Gene flow occurs of migrations, pollen by animals or wind in plant pouplations.
• Vestigal structure are anatomical structures that organisim and humans have but don't have a purpose of use anymore. For example Humans have a tail bone but there is no use for that anymore. The tail bone might have helped our tree-dweleing ancestors for travel and climbing between braches.
• Morphology is when homologous structures that have common ancestory but have different functions. For example the number of bones in human hand, bat wings and whale fins are similar but have different functions.
• Molecular evidence is comparing DNA sequences and amino acid sequences in proteins from different organisims that provided evidence of evolution.
• Naturual selection is the process where organisms adapt better to their environment to survive and produce more offspring. For example in the 1800's in Englad during the revolution, Sulfur Dioxide emissions from factories killed most of the light colored lichen in trees. Light colored moths were easily spotted by birds. The dark winged moths were favored because they were able to blend in with their environment better. By the 1950's almost 90% of the moths had darker wings. When pollution controls were introduced during the 1960's, linen was able to cover the trees again.
• Directional selection is occurs when one end of the the range of phenotypes is favored by natural selection. This causes the phenotype to increase over time. The moths is an example of this.
• Stabilizing selection is when the intermediate phenotype is favored and extreme phenotypes are selected against. In humans, birth weight is an example of stabilizing selection. Babies that are born too small can lose heat too easily and may die, where as babies being born too large can lead to complications during childbirth and the death of the mother or the baby.
• Distruptive selection is caused by natural selection where individuals on both extremes of the phenotypic range are more lileky to survive and reproduce that individuals with an intermediate phenotype. For example a habitate with light colored sand and dark colored rocks . Light mice could blend and be less visible to predators. Dark mice could blend with the dark colored rock. The intermediate phenotype in-between light and dark would be visible.
• Artifical Selction is when humans selectively Brees domesticated plants or animals. For example a farmers plants tomatoes.
• Sexual section is when individuals with certain characteristics are more likley to attract mates that other individuals. For example many bird choose mates ased on coloration, bird songs, mating dancing or nesting behavoirs. The blue- footed booby bird select mates with the brightest blue feet. Younger males have brighter blue feet and are more likely to have higher fertility.
• One possible cause of genetic drift is the bottleneck effect. The size of a population is greatly reduced for one or more generations. Natural disatsers like, fires, floods or volcanic eruptions can cause population bottlenecks. Human events such as overhunting or habitat destruction can cause population bottle necks. Which cause Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s. Hunting reduced their population size to as few as 20 individuals at the end of the 19th century.
• Another cause of the gentic drift is the founder effect The founder effect when a few memebers of large population start a new population. These members are more likely to have the same alleles as the original population. Grey butterflies and orange butterflies are examples of this.
• Hardy - weinberg equilibruim - 2

  Large population- reduces the chance of gentic drift occuring and a change in alleles because of genetic drift.

  Random mating- eliminates the possibility of changing allele frequencies caused by sexual reproduction

  No gene flow- change in the population including leaving or entering the population could change the allele frequencies.

  No selection- All phenotypes in the population is tgat veryone needs to have equal reproductive success to kee the allele frequencies stable.

  No mutations- A mutation would changethe allele frequencies
• P represents the dominate allele ( A )

  q represent the reccessive allele ( a )
• Phylogeny is the history of the evolution of a species or group.
• Phylogenetic trees and cladograms are hypotheses about the history of evolution over time