Chapter 20 Flashcards
Prokaryote vs Eukaryote DNA
Pro-1 circular chromosomes, no pairs
Euk- linear multiple chromosomes in pairs
Autosomal Chromosomes
Non sex
XX Female
XY male
Locus (Loci)
Location of Gene on chromosomes
Alleles
Alternative form of gene
Evolution
Change in allele frequency in a species over time
Phenotype=
Genotype + Environment
Physical appearance determined by genotype and environment
Genetic Variation
Differences in alleles of genes found within individuals in a pop.
Jean-Baptiste Lamarck
Epigenitics- Not changing DNA, turning on/off certain areas of genome
Natural Selection
1 Individuals in a pop. vary in traits
2 Traits can be heritable
3 Species with certain traits can survive and reproduce at higher rates than those without those traits
Population Genetics
Study of properties of genes in a pop. (Group of individuals of the same spp. in a given area)
Evolution results in a change in the genetic composition of a pop.
Genetic variation is the raw material for selection
In nature, genetic variation is the rule and is required for evolution to occur
Hardy Weinberg Equilibrium 5 assuptions
Allele equation
Genotype equation
No mutation
No migration
Random mating
No selection
Large population
Allele equation p (freq of dom allele) q (freq of recessive allele) p+q+1
p²+2pq+q²=1 (P² - freq of homoz dom) 2pq - Freq of heteroz (q² - freq of homoz rec)
Five agents of Evolutionary Change
Mutation
Gene flow
Nonrandom mating
Genetic Drift
Selection
Mutation
Rates generally low, other processes usually more important in changing allele freq. Ultimate source of genetic variation and makes evolution possible. Usually recessive
Gene Flow/Migration
Movement of allele from one population to another. Animal physically moves into a new pop. Drifting gametes or immature stages of plants or animals into area (Ocean current, wind blown seeds). Tends to decrease genetic variability between pops and reduces uniqueness
Nonrandom mating. Assortative vs Disassortative
Assortative mating-Phenotypically similar individuals mate. Increases proportion of homozygous individuals, inbreeding concerns (Can increase genetic disease).
Disassortative mating - phenotypically different individuals mate, produces excess of heterozygotes (White throated sparrow stripes and aggressiveness).
Genetic Drift
In small populations, allele freq may change by chance alone. Magnitude of genetic drift is inversely related to pop size. Can lead to loss of alleles in isolated pops and uncommon alleles are more vulnerable. Founder effect and bottleneck effect.
Founder Effect
One or a few individuals disperse and become the founders of a new, isolated pop. Some alleles are lost, other change in freq. Organisms on islands, self-pollinating plants, Amish, Finns
Bottleneck Effect
Drastic reduction in population size due to drought, disease, other natural forces. Survivors may constitute a random genetic sample of original pop. Results in loss genetic variability. Human hunting. Northern Elephant Seal, Bison
Selection (Natural vs Artificial)
Some individuals leave behind more progeny (young) than others, and the rate at which they do so is affected by phenotype and behavior.
Artificial selection - Breeders select desired characteristics
Natural selection - Environmental conditions determine which individuals produce the most offspring
Conditions to allow for Natural Selection
1 Variation must exist among individuals in a pop.
2 Variation among individuals must result in differences in the number of offspring surviving in the next generation
3 Variation must have a genetic basis (Not learned behavior or teaching)
Natural Selection vs Evolution
Natural Selection - Only one of several processes that can result in evolution
Evolution is the historical record, or outcome, of change through time
Insecticides
Led to rapid evolution of resistance in more than 500 pest spp.
Housefly pen gene decreases insecticide uptake. kdr and dld-r genes decrease target sites
Evolution resistance to antibiotics in many disease-causing pathogens
Fitness
Reproductive success and reflects how well an organism is adapted to its environment.
Individuals with one phenotype leave more surviving offspring in the next generation than individuals with an alternate phenotype
The relative concept is the most fit phenotype is simply the one that produces, on average, the greatest number of offspring
Selection favors phenotypes with the greatest fitness, phenotype increases in frequency
Components of fitness
Survival
Sexual selection - some more successful at attracting mates
Number of offspring per mating
Traits favored for one component may be a disadvantage for other
Water Striders
Large female water striders lay more eggs per day than small but survive for shorter periods of time. Intermediate sized females produce the most offspring over the course of their lives and thus have the highest fitness
Male vs female sexual selection
Females evaluate a male’s quality and then decide whether to mate
Most males only mate, don’t carry eggs, try to mate with as many females as possible
Parental Investment
The energy and time each sex invests in producing and rearing offspring
Females have a higher parental investment (typically)
Male Mormon crickets exceed normal by transferring a protein-containing packet to females during mating.
Sexual Selection-Intra vs Inter, secondary, dimorphism, sperm competition
Intrasexual selection - competitive interactions between members of one sex. Some males won’t mate, others a lot
Intersexual selection - Mate choice
Secondary sexual characteristics - antlers and horns used to combat other males, long tail feathers and bright plumage used to persuade opposite sex.
Sexual dimorphism - Differences between sexes (male larger than female, color)
Sperm competition - selects for features that increase probability that a male’s sperm will fertilize the egg
Intersexual selection Direct vs Indirect
Direct - Female benefit by choosing the male that can provide the best care. Males can provide territory for food and refuge.
Indirect - Higher-quality offspring. Choose the male that is healthiest or oldest. HANDICAP hypothesis - only genetically superior mates survive with a handicap such as a long tail that is a hinderance in flying
Sensory Exploitation
Evolution in males of a signal that exploits preexisting biases. Females respond to certain stimuli. Tungara frog, finches with feathers glued to head
Maintenance of variation Negative vs Positive frequency-dependent selection
Fitness of a phenotype depends on its frequency within the pop.
Negative freq- Rare phenotypes favored by selection, rare forms may not be in “search image” of predators, preyed upon less frequently. Water boatman - fish eat the most common color by more than chance alone
Positive freq- Favors common form, tends to eliminate variation, oddballs stand out and are picked off. ex. School of fish
Oscillating selection
Selection favors one phenotype at one time and another phenotype at another time. Effect will be to maintain genetic variation in the pop. over time. Medium ground finch of Galapagos, birds with big bills favored during drought, small bills favored during wet conditions
Heterozygote advantage
Heterozygotes are favored over homozygotes. Works to maintain both alleles in pop. Sickle cell anemia
Selection acting on traits affected by multiple genes
Many traits affected by more than one gene. Selection operates on all the genes for the trait. Changes the pop. depending on which genotypes are favored. Types - Disruptive, Directional, Stabilizing: and could oscillate
Disruptive selection
Acts to eliminate intermediate types. Two peaks form for ex. “large and small” not intermediate
Different beak size of African black-bellied seedcracker finch. Large beaks for big seeds, small beak for small seed. Intermediate sized beak is too clumsy for small seed not big enough for large seed
Directional Selection
Acts to eliminate one extreme. Ex. Fast over slow, or small over big. Often occurs in nature when the environment changes. In Drosophila, eliminated flies that moved toward the light, fewer in pop. over generations. New generations avoid light
Stabilizing selection
Acts to eliminate both extremes, makes intermediate more common by eliminating extremes. Humans, infants with intermediate weight at birth have highest survival rate.
Natural Selection in guppies
Above waterfall killifish rarely eat guppies, become larger more flashy
Bellow waterfall pike cichlid eat guppies, stay small, reproduce earlier, stay dull
Gene flow constructive vs constraining
Constructive - spread beneficial mutation to other populations
Constraining - Can impede adaptation by continual flow of inferior alleles from other populations
Examples
Eyes on insect, not genetic environment, not evolution
Thoroughbred horses speed
