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

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



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

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

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 reproduction because males or females prefer them non random mating intrasexual and intersexual selection Sexual dimorphism Individuals of most sexually reproducing organisms have a distinct male or female phenotype common in mammals and birds Adaptation and Variation Recombination Sexual selection and sexual dimorphism How does this condition come about and what maintains it Nonrandom mating selects for alleles from preferred traits that prevail over generations Females are often the main agents of selection Ex humans Hybridization Form of crossbreeding Sexual reproduction between 2 different species Usually results in infertility low sperm or egg count or sterility no viable sperm or egg Ex Mule male sterile female infertile Adaptation and Variation Maintaining two or more alleles Balanced polymorphism 2 or more alleles for a trait in a population persist over time non identical alleles for a trait are maintained at frequencies 1 frequencies may shift but over time often return to the same value Ex sickle cell anemia HbS mutant form of hemoglobin HbS HbS homozygotes develop sickle cell anemia sickle shape RBC HbA HbA homozygotes are normal biconcave RBC HbA HbS heterozygotes have both normal and sickle shape RBC Frequency of Hbs in tropical and subtropical regions of Asia and Africa is higher than expected up to 1 3 of pop is HbA HbS Adaptation and Variation Balanced Polymorphism sickle cell anemia Why is the frequency of HbS in tropical subtropical regions of Asia and Africa so high HbS HbS HbA HbA HbA HbS homozygotes often die due to sickle cell homozygotes often die in these regions due to malaria heterozygotes make up 1 3 of the human population Why is this combination of alleles maintained at such high frequencies 300 million year infected HbA HbS frequency of heterozygotes are highest where malaria incidence is highest HbA HbS heterozygotes more likely to survive recurring infections Plasmodium Adaptation and Variation Balanced Polymorphism sickle cell anemia HbA HbS this allele combination produces two forms of hemoglobin 1 non mutated cells maintain body function 2 mutated cells interfere with circulation ability to infect new cells This slow down in circulation interferes with the parasites ability to rapidly infect new cells Natural selection favors the HbA HbS heterozygote because is enhances fitness where malaria is prevalent HbA HbS has a higher fitness than HbS HbS and HbA HbA in these tropical regions selective force for over 200 yrs Adaptation and Variation Types of variation quantitative continuous Ex height weight etc of individuals 1 Normal variation X discreet Ex eye color blood groups Measured trait variation along a ecological or geographic gradient can occur as a cline Ex plant morphology along H2O gradient of individuals 3 Ecogeographic variation South north 2 Polymorphic variation of individuals Measured trait Measured trait


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