Forces of Evolution Flashcards
a change in the heritable characteristics of biological populations over successive generations
EVOLUTION
Change in the gene pool of populations over time
EVOLUTION
What changes populations?
evolutionary forces
Evolutionary Forces
- Genetic drift
- Gene flow
- Mutation
- Natural Selection
a heritable factor that can control a specific characteristics
gene
specific forms of a gene differing by one or a few bases and occupying the same gene locus
alleles
made up of DNA and proteins
duplicated chromosome
the whole of the genetic information of an organism found in the nucleus of eukaryotes
genome
difference between gene and DNA
gene - sequence of DNA / RNA that codes for a molecule that has a function the transmission of genes to an organism’s offspring is the basis of the inheritance of phenotypic traits
DNA - a molecule composed of two chains which coil around each other to form a double helix carrying the genetic instructions used in the growth, development, functioning of all known living organisms
collection of genes within a population
Gene Pool
indicates the alleles that the organism has inherited regarding a particular trait (Letters)
Genotype
The actual visible trait of the organism
Phenotype
provides a framework for understanding how populations evolve;
is a type of model. Biologists use model to study populations. Note: individuals do not evolve, populations do EVOLVE.
Hardy-Weinberg equilibrium
The Hardy-Weinberg Principle
p^2 + 2pq + q^2 = 1
p^2: frequency of homozygous dominant genotype
2pq: frequency of heterozygous genotype
q^2: frequency of homozygous recessive genotype
states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.
The Hardy-Weinberg Principle also known as the Hardy-Weinberg equilibrium, model, theorem, or law
is used to predict genotype frequencies in a population.
is based on Mendelian genetics. It is derives from a simple Punnett square in which p is the frequency of the dominant allele and q is the frequency of the recessive allele.
The Hardy-Weinberg equation
Genotypic frequencies stay the same if all these conditions are met. (5)
- very large population: no genetic drift
- no emigration or immigration: no gene flow
- no mutations: no new alleles added to gene pool
- random mating: no sexual selection
- no natural selection: all traits aid equally in survival
- a random evolutionary change.
- changes allele frequencies within a population due to CHANCE alone.
- it may happen that some alleles are completely lost within a generation due to ______, even if they are beneficial traits.
- it is not expected to results in adaptation to the environment because it is CHANCE EVENTS rather than natural selection that determines which individuals will reproduce.
genetic drift
Small populations are ______ affected by genetic drift. In large populations, such random events are ______.
hugely,
insignificant
Two types of genetic drift
bottleneck effect
founder effect
SUDDEN SHARP DECLINE in a population’s size since sometimes, a population is subjected to near extinction because of a natural disaster such as earthquake, fire or slaughter by humans.
CHANCE ALONE determines which individuals survive these unfavorable times, preventing the majority of genotypes from participating in the production of the next generation.
bottleneck effect
bottleneck effect example
Case study of the Northern Elephant Seal
100,000 (early 1800’s)
50 (due to hunting)
150,000 (present-day)
Southern Elephant Seal
- ‘no environmental pressure’
DNA (mitochondrial)
- researchers found out that diversity in pre-bottleneck was _____ than in post-bottleneck.
- present population looks very similar than the ‘pre-bottleneck’ population
higher
Symmetry indicates _____ in a population
‘fitness’
forming of new colonies;
newly founded populations don’t always represent the genetic diversity in their sources.
Founder effect
the transfer of genes from the gene pool of one population to another
- change the allele or gene frequencies in the population
gene flow (gene migration)
example of gene flow in plants
plant populations can experience gene flow by spreading their pollen long distances away to other populations by means of wind or through birds or insects
What does gene flow do to the populations?
- maintains variation within a population
- reduces variation between populations
- permanent alteration of the nucleotide sequence of the genome of an organisms
- are the ONLY ORIGINAL SOURCE OF ALLELE CHANGES
- _____ rates are quite low
Mutations
Effects of germ line mutations
A single germ line mutation can have a range of effects
a.) No change occurs in phenotype
b.) Small change occurs in phenotype (ex: Scottish Fold)
c.) Big change occurs in phenotype
- when mutation occurs in a stretch of DNA with no function
- or perhaps mutation occur in a protein-coding region, but ends up not affecting the amino acid sequence of the protein
NOTE: more the 90% is non-coding
No change occurs in phenotype
How does mutation affect protein formation?
By changing a gene’s instructions for making a protein, a variant can cause a protein to malfunction or to not be produced at all.
PROTEINS CODES DNA AND RNA.
is the process in which RNA codons are decoded into amino acids that make up an amino acid chain (a polypeptide)
Translation
Types of Mutation
- Silent point mutation
- Missense point mutation
- Nonsense point mutation
- Insertion mutation (frameshift)
- Deletion mutation (frameshift)
- Inversion mutation
- Translocation mutation
Change one nucleotide to another but do not change the amino acid sequence of the protein
Silent point mutation
Change one nucleotide to another, resulting in a different amino acid sequence of the protein
Missense point mutation
Change the DNA sequence in a way that results in an early stop codon
Nonsense point mutation
Insert one or more extra nucleotides into the DNA sequence.
often alter the reading frame of the gene such that every codon after the insertion is altered.
Insertion mutation
Remove one or more nucleotides from the DNA sequence such that the reading frame is altered. Every codon after the _______ is altered.
Deletion mutation
A group of DNA nucleotides are turned over to be read in reverse order. This changes the amino acid sequence in that location.
Inversion mutation
The movement of segments of DNA from one chromosome to another can fuse portions of different genes together.
Translocation mutation
- mutations that occur in non germline tissues,
- cannot be inherited,
- DO NOT MATTER FOR EVOLUTION,
- frequently caused by environmental factors e.g. exposure to UVR or to certain chemicals
Somatic mutations
mutations present in egg or sperm, can be inherited, cause cancer family syndrome
Germline mutations
- is the process by which population become adapted to their environments
- organisms that are better adapted to an environment are more likely to survive and reproduce than organisms that are less well adapted
Natural Selection
Factors that affect natural selection
- overproduction
- adaptation
- competition
- variation
- nonrandom mating
- positive assortative mating
- physical location
Most species produce far more offspring than will/can survive
Overproduction
- Malthus’ Basic Theory
- Point of Crisis
A key to variation is _________.
Sexual reproduction
-when individuals nonrandomly mate with other individuals
- individuals prefer mates
- hence, traits that lead to more mating for individuals lead to a higher frequency of that train in the population
Nonrandom mating
(Sexual Selection)
individual preference to mate with partners that are phenotypically similar to themselves
positive assortative mating
