Evolution Lecture 5

Evolution Lecture 5 - Evolution Lecture 5 Mutation source...

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Evolution Lecture 5 Mutation: source of all new alleles. There is no other choice. There are a variety of ways that mutation can occur at the level of DNA, but the ultimate effect is to produce a new allele that follows Mendel’s law. Once these new alleles are there, we have a new type in the population which will follow Hardy Weinberg. Types of mutations: Point mutation: change in the single nucleotide. Duplication and deletion. Mutations also result in the duplication in whole chromosomes. If there is no reduction division during meiosis, a gamete is formed which is diploid: two copies of chromosomes. Then if that gamete fertilizes another gamete that has also failed to undergo reduction division, you’ve crated a gamete with 4 chromosomes instead of 2. Most of the time the cell can’t develop but when it does you get a genome with twice as many genes. Point mutations, deletions, and duplications are the primary way new alleles are formed. These events occur at very low rates. There is so much DNA in each organism, that every newborn carries new mutations. Most of these mutations will have no effect; the individuals won’t even know they have them. Sometimes there is a large effect and a new type appears which is either advantageous or disadvantageous. Mutations are occurring all the time, they are the ultimate source of all variation, and Mutations solve a problem that Darwin had. Why doesn’t variation disappear? Because every generation’s slight errors in DNA replication are creating new types. This was not known to Darwin though, ittwas known 50 years after The Origin. Random mating alone does not change allele frequencies. They are the same in the offspring as they are in the parents. In Neo Darwinism, evolution occurs because of changes in allele frequencies. Something has to change allele frequencies: Darwin said it was natural selection. It is responsible for changing allele frequencies in the following way: Natural selection is responsible for preserving the types that are given advantage in the struggle for existence. Mendelism says that “what is the type that is preserved?” What is preserved is an allele or group of alleles that gives an individual an advantage in the struggle for existence. Its not enough to have a type that is somehow better; this type has to be associated with an allele so that this allele can be transmitted to its offspring. We have duality: Phenotypes are the characteristics that Darwin studied in detail, and the Genome. They are both related. Phenotype is strongly affected by genotype. But phenotype is not transmitted to the offspring. When you go to the offspring, the genotype is inherited from the two parents and then the genotype produces the phenotype. We have two levels of Biology: The level of the observable type: Phenotype which interacts with nature and the physical environment. And then you have the Genome which is the only thing that is capable of being transmitted. The other part of Neo Darwinism is that
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This note was uploaded on 02/04/2010 for the course BIO 1B taught by Professor Carlson,mischel,power during the Spring '07 term at Berkeley.

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Evolution Lecture 5 - Evolution Lecture 5 Mutation source...

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