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BIO120H1 Study Guide - Gene Pool, Eye Color

Course Code
Jean Jiang Nash

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Evolution + Adaptation 03:24
Darwins Finches
El Nina -> harder seeds -> finches w/ bigger beaks survived better
Avg beak size of surviving indivi + progeny inc
El Nino -> smaller seeds ->smaller beaks survive better
Prod more offspring vs. larger beaks
Avg size -> lower value
Capacity of pop to rsp to changes in env
Traits of indivi w/in pop = continually adjusted to changes in env
Humans = products of genes
Differ in genetic makeup
Indivi w/ particular makeup prod greater # of offspring
Some variations of genes will be passed on to future generations more freq vs. others
Become predominant in pop
Changes appear slowly
Orgs can rsp to changes in env
Pop evo + indivi rsps enable species to adapt to cond of its env
Phenotype = outward expression of an indivis genotype
Genotype = indivis genes
Set of genetic instruction
Phenotype = outward expression of genotype in indivis structure + function
Rendering/expression of genotype in form of an org
Genetic makeup of indivi sets limits on phenotype expression
Phenotypic traits have genetic basis + influenced by variations in env
Effects of env conditions on indivi
Behavioral + physiological rsps of indivi to exhibit diff rsps to env
= phenotypic plasticity
Genetic Variation
Alleles = diff forms of a particular gene
Create perceptible + measureable diffs in an orgs phenotype
EX. ABO blood types
Gene prod antigens A + B (O doesnt prod antigens)
Molecules that interact w/ immune sys
Blood type A: AA / AO genotypes
Blood type B: BB / BO genotypes
AB or OO genotypes
Link b/w genotype + phenotype = direct
AA father + BB mother = AB geno
EX. Eye colour in humans
Several genes acting together
Reflects influence of at least 3 genes
Control pigments of diff parts of phenotype inheritance

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Depend on interactions among the genotypes of each gene
Each indivi = 2 copies of each gene
1 from mother, 1 father (except sex-linked genes)
heterozygous = 2 diff alleles of a particular gene (AB)
2 diff alleles prod intermediate phenotype
1 allele masks the expression of the other
dominant allele
recessive allele
most harmful alleles = recessive
homozygous = 2 copies of a gene are the same (AA)
Gene pool = all alleles of all the genes of every indivi in a pop
Sexually reproducing pop contain lot of genetic variation
United States: 61.3% O, 30.0% A, 8.7% B allele
Asians: higher B allele, Irish = O alleles
Sources of Genetic Variation
From any change in sequence of nucleotides (ATCG) that make up gene
Rearrangement of DNA molecules
Inverted regions, duplicated, exchanges of DNA sequences b/w chromosomes
Lethal changes in phenotype
Alter appearance, physiology, beh (esp simple nucleotide substitutions)
EX. Tay-Sachs disease, cystic fibrosis, albinism
Silent/synonymous mutation
No detectable effect
Mutations have multiple effects
EX. Gene: daf-2
Lengthens life span of roundworm
Mutant daf-2 allele
Infl expression of other genes + gene regulators
Results in many diff effects on life span + physiological processes
Pleiotropy = effect of single gene on multiple traits
Genetic bass of continuously varying phenotypic traits
EX. Body size
Most pops, indivi exhibit normal/bell-shaped distribution
Concentration of indivi toward middle, fewer towards large + small extremes
Due to diffs in env indivi exp during development
Actions of genes
Each have small infl

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Allele tends to inc body size
Alternate allele tends to dec body size
Size of indivi dep on mix of alleles for all of the genes in its genome
Adaptations result from natural selection on heritable variation in traits that affect evolutionary
Evolution = any change in a pop’s gene pool
Process of evo by natural selection
1. Variation among indivi
Diffs in particular trait among indivi in a pop
2. Inheritance of that variation
Genetic basis of evo
Heritable traits remain stable, passed from parent -> offspring
Trait/heritable underlying genetic infl
= part of makeup of the pop as a whole
3. Differences in survival + reproductive success/fitness related to that variation
Fitness = production of descendants over an indivis lifetime
More offspring = greater fitness
Heritable traits that promote reproductive success = passed on at high rate + replace lower fitness
EX. California citrus pest
Species of scale insect = serious pests in citrus orchards
Controlled by fumigating orchards w/ cyanide gas
Killed fewer + fewer
Insects – evolved genetically based resistance to cyanide poisoning
Killed most at first
Indivi w/ alleles for cyanide resistance reproduce + left offspring
Resistant indivi inc -> all indivi resistant
Any phenotypic variation can cause variation in fitness among indivi
Traits of indivi that leave the most offspring = selected
Natural selection
Differential survival + reproduction of indivi having different traits
Artificial selection
Conscious decisions made by humans abt desirable qualities of domesticated/lab anms + crops
Env can infl phenotype directly
Variation in availability of food – prod variation in body size
Sometimes improve relationship to env
Acclimatization – beneficial changes but not evo
Creates phenotypic variation in pop
Differential survival + reproduction
Gene pool remains unchanged bc no genetic basis for variation
Natural selection has no goal
Occurs bc of diffs in reproductive success among indivi w/ diff forms/functions in env
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