Chapter 23 Flashcards
What determines phenotypic differences?
Changes in a single gene or influences from multiple genes along a continuum
Where do new genes come from?
Mutation; gene duplication; genetic variation from sexual reproduction
Is mutation always harmful?
Not always, but in the case of point mutation usually
Reproduce quickly and have very short generation times
Prokaryotes
What are 3 mechanisms that cause allele frequency change?
1) natural selection
2) genetic drift
3) gene flow
How allele frequencies often fluctuate unpredictably from one generation to the next, especially in smaller samples. This reduces genetic variation
Genetic drift
Movement of alleles among populations through the movement of fertile individuals/gametes. Reduces genetic variation over time.
Genetic flow
What are the 3 modes of selection?
1) directional
2) disruptive
3) stabilizing
Favors individuals at extremes of phenotypic range
Directional selection
Favors individuals at both extreme ends
Disruptive selection
Favors intermediate variants within the phenotypic range
Stabilizing selection
What is a common misconception about organisms and evolution?
That organisms evolve during their lifetimes. Only populations evolve, and that takes time
What cause genetic variation among individuals?
Differences in genes or other DNA segments
How can sexual reproduction result in genetic variation?
By recombining existing alleles
Can all mutations be passed on to offspring?
No, only mutations in cells that produce gametes
Mutation rates are often lower in ___ and higher in ___
Prokaryotes; viruses
A localized group of individuals capable of interbreeding and producing fertile offspring
Population
What does a gene pool consist of?
All of the alleles for all loci in a population
What makes a locus fixed?
If all individuals in a population are homozygous for the same allele
Consists of changes in allele frequency in a population over time
Microevolution
Refers to broad patterns of evolutionary change above the species level
Macroevolution
A group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring
Species
The existence of biological factors (barriers) that impede two species from producing viable, fertile offspring
Reproductive isolation
How do prezygotic barriers block fertilization from occurring?
1) impeding different species from attempting to mate
2) preventing successful completion of mating
3) hindering fertilization if mating is successful
When two species encounter each other rarely, or not at all, because they occupy different habitats, even though not isolated by physical barriers
Habitat isolation
What do postzygotic barriers prevent?
The hybrid zygote from developing into a viable, fertile adult
Give an example of how gene flow can occur between distinct species
The mating of a polar bear and a grizzly bear to make a grolar bear
What types of species does the morphological species concept apply to?
Sexual and asexual species
Defines a species as the smallest group of individuals on a phylogenetic tree
Phylogenetic species concept
The presence of extra sets of chromosomes due to accidents during cell division
Polyploidy
What is the cause of genetic variation among individuals?
Caused by differences in genes or other DNA segments
When does the founder effect occur?
When a few individuals become isolated from a larger population
Duplication of small pieces of DNA ___ genome size and is ___ harmful.
Increases; less
Genetic drift tends to ___ genetic variation through ___ of alleles
Reduce; loss
Natural selection can cause ___ evolution, an improvement in the match between organisms and their environment
Adaptive
When one base changes in a gene
Point mutation
Can mutations that cause change in protein production be harmful?
Yes
All the alleles for all loci in a certain population
Gene pool
What is the formula for Hardy-Weinberg equilibrium?
p2+2pq+q2=1
What are the 5 conditions for non-evolving populations? (Conditions for Hardy-Weinberg equilibrium)
1) no mutations
2) random mating
3) no natural selection
4) very large population
5) no gene flow
Drastic reduction in population size because of changes in the environment
Bottleneck effect
Movement of alleles in populations
Gene flow
An improvement in the match between organisms and their environment
Adaptive evolution
Marked differences between the sexes in secondary sexual characteristics
Sexual dimorphism
When does heterozygotes advantage occur?
When heterozygotes have a higher fitness than both homozygotes
A change in allele frequencies in a population over generations
Microevolution
What are some reasons natural selection cannot fashion perfect organisms?
- can only work on existing variations
- evolution is limited by historical constraints
- adaptations are often compromises
- chance, natural selection, and environment interact
What causes genetic variation?
Differences in genes or other DNA segments
If there are 2 or more alleles for a locus, diploid individuals can be what?
Homozygous or heterozygous
Genetic drift is significant in ___ populations
Small
Gene flow can ___ the fitness of a population
Decrease
What can be caused by a mutation in the hemoglobin protein?
Sickle-cell disease and malaria
Direct competition among individuals of one sex (often males) for mates of the opposite sex
Intersexual selection
Favors intermediate variants and acts against extreme phenotypes
Stabilizing selection
Favors individuals at one extreme end of the phenotypic range
Directional selection
Favors individuals at both extremes of the phenotypic range
Disruptive selection
Contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals
Relative fitness
What are two examples of genetic drift?
Bottleneck effect and the founder effect
Organisms of one sex directly compete for mates of the opposite sex
Intrasexual selection
Organisms of one sex are choosy in their selection of the opposite sex
Intersexual selection
Name some effects of genetic drift
- occurs in small populations
- causes allele frequencies to change at random
- loss of genetic variation in a population
- causes harmful alleles to be fixed
The product of inherited genotype and environmental influences
Phenotype
In a population where gametes contribute to the next generation randomly and Mendelian inheritance occurs, allele and genotype frequencies remain constant from generation to generation. Such a population is in ___
Hardy-Weinberg equilibrium
Natural selection for mating success. Can result in sexual dimorphism, marked differences between the sexes in secondary sexual characteristics
Sexual selection
Recombination from crossing over in meiosis is the source of ___
Genetic variation
A trend toward the decrease in size of plants on slopes of a mountain as altitude increases is an example of ___
Cline
All geographic variation results from ___
Clines
