Chapter 5 Flashcards
– a mechanism that explains how the diversity of organisms inhabiting our world have acquired the features seemingly designed to enable them to survive and reproduce
Theory of Natural Selection
the differential success (survival and reproduction) of individuals within the population that results from their interaction with their environment
natural selection
Natural selection is a product of two conditions (as outlined by Darwin). What is the two conditions?
(1) that variation occurs among individuals within a population in some “heritable” characteristic, and
(2) that this variation results in differences among individuals in their survival and reproduction as a result of their interaction with the environment
measured by the proportionate contribution it makes to future generations of an individual
fitness
changes in the properties of populations of organisms over the course of generations which the result of natural selection
evolution
any heritable behavioral, morphological, or physiological trait of an organism that has evolved over a period of time by the process of natural selection such that it maintains or increases the fitness (long-term reproductive success) of an organism under a given set of environmental conditions
adaptation
represent the characteristics (traits) that enable an organism to survive, grow, and reproduce under the prevailing environmental conditions
adaptation
structural adaptation
- teeth
- body coverings for defense
- movement
- fish snout: superior, terminal, inferior
- caudal fin: lunate, forked, truncate, rounded, continuous
- colouration: counter shading, mottled, mimicry, stripe
This adaptation involves some part of an animal’s body.
structural adaptation
A form of camouflage where an animal’s underside is lighter and its back is darker, helping it blend with both sky and ground or water.
Counter shading
Behavioral adaptations
type of fish migration
hibernation
being nocturnal
explains this survival and shows how species can change over time. For example, certain traits of adaptations involving color, camouflage, food gathering (beaks and claws) and other physical traits, sensory abilities or behaviors enhance the survival of a species.
natural selection
natural selection examples
o Monarch butterflies
o Finches from Galapagos Archipelago
the Units of Inheritance
genes
form the informational units of the DNA molecule
genes
genetic material that codes for a functional product
genes
alternate forms of a gene; (Greek) allelomorphs = “different form”
alleles
process by which DNA is used in the synthesis of products such as protein
gene expression
collectively all of the DNA in a cell
genome
microscopic, threadlike bodies by which genes are arranged in linear order
chromosomes
position occupied by a gene on the chromosome; (Latin) locus = place
locus
two copies of each type of chromosome in each individual cell of a most multicellular organisms
homologous chromosomes
pair of alleles present at a given locus of an individual
genotype
set of alleles
genotype
two main categories of genotypes:
homozygous
heterozygous
two copies of the gene are the same
homozygous
two alleles at the locus are different
heterozygous
the Physical Expression of the Genotype
Phenotype
outward appearance of an organism for a given characteristic
Phenotype
the external, observable expression of the genotype
Phenotype
the allele that is expressed in which one allele masks the expression of the other
dominant allele
the allele that is masked
recessive allele
the allele if the physical expression of the heterozygous individual is intermediate between those of the homozygotes
incomplete dominance
phenotypic characteristics that fall into a limited number of discrete categories
qualitative traits
Two reasons why the continuous distribution of most phenotypic traits occurs:
- more than one gene locus affecting them
- environment
continuous distribution of traits, such as height or weight
quantitative traits
ability of a genotype to give rise to different phenotypic expressions under different environmental conditions
phenotypic plasticity
set of phenotypes expressed by a single genotype across a range of environmental conditions
norm of reaction
the phenotypic plasticity occurs during the growth and development of the individual and represents an irreversible characteristic
Developmental plasticity
reversible phenotypic changes in an individual organism in response to changing environmental conditions
Acclimation
What is the development of the low-light plant vs the high-light plant?
- low light: more photosynthetic leaf area, thin leaves, less biomass, few branches
- high light: narrow leaves, more biomass, many branches
phenotypic trait that selection acts directly upon
target of selection
genetic variation occurs among subpopulations of the same species
genetic differentiation
the sum of genetic information (alleles) across all individuals in the population
gene pool
represents the total genetic variation within a population
gene pool
the environmental cause of fitness differences among organisms with different phenotypes
selective agent
three general types of natural selection:
directional selection
stabilizing selection
disruptive selection
type of natural selection, in which the mean value of the trait is shifted toward one extreme over another
directional selection
natural selection may favor individuals near the population mean at the expense of the two extremes
stabilizing selection
occurs when members of a population are subject to different selection pressures
disruptive selection
can be defined as a change in the mean or variance of a phenotypic trait across generations as a result of changes in allele frequencies
phenotypic evolution
product of natural selection
adaptations
