UCSB EEMB 2 - Lec #12 EEMB 2 SM17 1S (Sources Types of Variation) (1) (11 pages)

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Lec #12 EEMB 2 SM17 1S (Sources Types of Variation) (1)



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Lec #12 EEMB 2 SM17 1S (Sources Types of Variation) (1)

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Pages:
11
School:
University of California, Santa Barbara
Course:
Eemb 2 - Introductory Biology III

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Adaptation and Variation Sources of Variation 1 Mutation 2 Recombination Mutation heritable changes in DNA genes that give rise to altered gene products 1 The only source of new alleles increases allelic variation 2 New alleles may alter the amino sequence of the encoded protein altering the function of the protein 3 Wild type alleles produce expected phenotypes mutant alleles may produce an unexpected phenotype Mutations give rise to structural functional or behavioral modifications that can increase decrease or are neutral to an individuals survival and reproduction Adaptation and Variation Types of Mutations In multicellular organisms only mutations in cell lines that produce gametes can be passed to offspring not somatic cells Chromosomal mutation deletions duplications inversions translocations not common usually negative may be lethal occasionally positive Point mutation addition subtraction substitution of nucleotide base s due to errors in DNA replication or environmental mutagens DNA mutations can result in changes in mRNA proteins Silent no effect on protein Missense reduce efficiency of protein Nonsense non functional protein mutations more common can be positive negative or neutral Adaptation and Variation Types of Mutations negative mutations bestow a disadvantage in terms of survival and reproduction positive mutations bestow an advantage in terms of survival and reproduction neutral mutations may become advantageous after environmental change Most mutations are neutral or negative but even if advantage is small chance events or natural selection may preserve or enhance the frequency of the mutant gene representation in the next generation Adaptation and Variation Mutations Mutations are rare Each gene has a mutation rate difficult to determine when and in which individual they will appear Mutation frequency is usually lower than 1 per 104 109 base pairs per DNA replication rare event Rates are sufficient to create genetic variation because many genes mutate genes may rearrange simultaneously and populations have large amounts of individuals Beneficial neutral mutations have accumulated for billions of years Mutations the raw material for evolutionary change Leads to the large biological diversity past and present Provides the genetic diversity that natural selection acts on Adaptation and Variation Recombination Sexual reproduction combines alleles from 2 parents fertilization Inbreeding Sexual reproduction between 2 genetically similar individuals of the same species Increase the genetic load of potential harmful negative genes decrease the amount of variation in a population Crossbreeding Sexual reproduction between 2 genetically different individuals of the same species decrease the genetic load of potential harmful negative genes increase the amount of variation in a population Adaptation and Variation Recombination Sexual reproduction Sexual selection Traits being favored are advantageous with respect to survival and



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