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BILD 3 Lecture 2
Lecture 2 terms and concepts
24
Biology
Undergraduate 2
08/06/2010

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Term
The Hardy-Weinberg Theorem
Definition

  • A null model
  • Describes a population that is not evolving
  • If no other forces are at work, the frequencies of alleles and genotypes in a population's gene pool remain constant from generation to generation.

Term
gene/allele
Definition
the functional unit of heredity
Term
locus
Definition
location on a chromosome
Term
homozygote
Definition
same 2 alleles at a locus (AA, A1A1, etc)
Term
heterozygote
Definition
different alleles at a locus (Aa, A1A2, etc)
Term
gametes (egg & sperm) are haploid or diploid?
Definition
haploid
Term
zygote (fertilized egg) is haploid or diploid?
Definition
diploid
Term
Assumptions of Hardy-Weinber Equilibrium Principle
Definition

  1. No selection (fitness)
  2. Mating is random
  3. Population is infinitely large
  4. No gene flow from outside population
  5. No mutation

Term
Why is a null model useful?
Definition
Researchers can compare real-life genotype frequencies to model, if population is not in HW, at least one of the assumptions is being violated.
Term
Why are there more heterozygotes than expected?
Definition

  • heterozygotes are more fit (violates "no selection" of null model)

Term

Individuals with higher fitness contribute _____ gene copies to the next generation than less fit individuals.

 

Dependent on: reproduction or survival?

Definition

more;

 

reproduction

Term
The nature of selection: acts on _____, but only the ______ is heritable
Definition
phenotypes; genotype
Term
Phenotype
Definition
the characteristics of an organism, due to both the genes and the environment
Term
Genotype
Definition
genetic composition of an organism
Term
_________ + _________ = Phenotype
Definition
Environment + Genotype
Term
Three modes of selection are:
Definition

-Directional

-Disruptive

-Stabilizing

Term
Directional selection
Definition

  • the extreme phenotype is the most fit
  • will change population mean
  • will slightly decrease variation

Term
Stabilizing selection
Definition

 

  • intermediate phenotypes are most fit
  • will NOT change population mean
  • will decrease variation
  • most common form of selection
Ex: female fly lays egg on goldenrod, egg hatches & larvae burrows into plant stem, induces plant to produce a gall, and it is presumed the the gall protects fly larvae from predators

 

Term
Disruptive selection
Definition

  • two extreme phenotypes are more fit than intermediate phenotypes
  • will NOT change population mean
  • will increase variation

Term
Neutral variation
Definition

  • It is a genetic variation that appears to confer no selective advantage or disadvantage
  • Neutral variation cannot be removed by selection

Term
Diploidy
Definition

  • Maintains genetic variation in the form of hidden recessive alleles
  • Recessive alleles in heterozygotes are not subject to selection

Term
Balancing selection
Definition

  • Occurs when natural selection maintains stable frequencies or two or more phenotypic forms in a population
  • Leads to a state called balance polymorphism
  • Heterozygote advantage and frequency-dependent selection are two forms of balancing selection

Term
sickle-cell allele
Definition

  • Causes mutations in hemoglobin but also confers malaria resistance
  • Exemplifies the heterozygote advantage

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