Microevolution and population genetics (2)

Microevolution

genetic changes within populations

Basic Evolution

• Change through time

• Decent with modification

Descent with modification

• Evolutionary changes that have accumalted over time since two lineages split

• Change in environment → natural pressures → remove those that are not fit → those who do fit reproduce and pass on genes

• Environment is always changing and not known

Pangenesis

• Incorrect

• Gametes are result of gemmules (features of every facet of organism) produced small packages of what they are → go into offspring → create a new organism 

• Believed acquired characteristics (scars, skills) were inherited

Why is Pangnesis incorrect?

• acquired characteristics are developed over a life time

• Acquired traits result from changes in an organism's phenotype, not its genotype. Since they don't change the genetic code, they can't be passed on to the next generation.

genotype

• The genetic makeup of a cell or organism; the particular combination of alleles present in an individual.

• ATGC, actual DNA sequence

• Individuals genotype is set of alleles possessed by the individual

genotype frequency

The proportion of a specified genotype among all the genotypes for a particular gene or set of genes in a population.

genotype-by-environment interaction

• Unequal effects of the environment on different genotypes, resulting in different phenotypes.

• ex: Height potential part of genotype, but environment (ex: malnutrion) can change phenotype?

What is biological evolution

• change in allele or genotype frequencies in populations over time

Why do islands show evolution so well?

•  geographically isolated from mainland → large ecological opportunity, no comp, genetic variation → radiated across islands → specification events across diff. Environments on islands

Theodosius Dobzhansky

• Genetics and the Origin of Species

• saw speciation events in Hawaii

Adaptive radiation

when Organisms diversify rapidly from an ancestral species when a change in the environment makes new resources available, creates new challenges, or opens new environmental niches

Phenotype

• The expressed physical, behavioral, and biochemical traits of an individual, including height, weight, eye color, and so forth.

•  phenotypes are underlined by genotype frequencies and allele frequencies 

Selection pressure genotype vs. phenotype

• Phenotype: Natural selection acts on an organism’s phenotype (observable features)

• Phenotype is often largely a product of genotype (the alleles, or gene versions, the organism carries).

• When a phenotype produced by certain alleles helps organisms survive and reproduce better than their peers, natural selection can increase the frequency of the helpful alleles from one generation to the next – that is,

• it can cause microevolution.

Who created penicillin?

Alexander Fleming, 1928

What is penicillin a product of?

Product of Penicillium mold

What kind of drug is penicillin?

• First antibiotic drug based on a naturally occurring substance

What issue occurred with penicillin?

• • Represents an evolved response to bacteria

• the spread of antibiotic resistant in bacteria reduced effectivess of penicillin over time

Microevolution

• Changes within species,

• Pushed by Natural selection and Other evolutionary forces

what does microevolution depend on"?

• heritable variation in population genetics

What is a population?

• individuals on species at same time and place

• Need to Produce fertile offspring and productive

what are traits under?

• can be under strong natural selection

• e.g. antibiotic resistance

what is phenotypic variation?

 heritable variation in appearance and/or function

What is qualitative variation

• Type of phenotypic variation

• characteristics with distinct states

what are polymorphisms?

•  Any genetic difference among individuals that is present in multiple individuals in a population.

• Under qualitative variation

• distinct variants of character

• e.g., presence of spines = Yes or No

How are polymorphisms impact by natural selection?

• States can be more useful in certain times and places

• Ex: red ladybug survives because they are predated less on than black ladybug population

Quantitative variation

• type of phenotypic variation

• Characteristics with a range of variation

• Controlled by multiple genes

• Can be measured (e.g., height)

when do characteristics have a wider range?

• Trait does not have strong pressure to conform to a certain way

When do characteristics converge to a mean?

• There is strong natural selection for that specific trait

Are genotypes and phenotypes completely correlated?

• Phenotypic variation is due to genetics, environmental differences, or both

• Only genetic component of phenotype are heritable

Are there experiments we can use to determine connection between phenotypes and genotypes?

1. Keep genetics constant (clones), vary environment

2. Breeding and selection experiments

   1. how to determine if variation is influenced by genetics

      1. Evolution can only act on heritable variation

Law of segregation

Organisms carry two alleles per trait, which segregate during gamete formation, so each gamete carries one allele per trait. Offspring receive one allele per parent.

Law of independent Assortment

The inheritance of one trait is independent of the inheritance of another, as long as the genes for the traits are on different chromosomes.

Law of dominance

In a pair of alleles, one may be dominant, masking the effect of the other, which is recessive

What causes genetic variation?

1. new alleles from mutations

2. Recombination followed by segregation of homologous chromosomes during meiotic cell division shuffles to create new combinations

what are Germ-line mutations?

• occur in reproductive cells and present in sperm or eggs

• passed down to the next generation

What is recombination?

• occurs when genetic variation is already present

• takes place in meiosis production of sperm and eggs

• causes segments of DNA to be shuffled from chromosome to chromosome

What can recombination occur from?

• organisms crossing over

• independent assortment

• random fertilization

What is population genetics?

• The study of patterns in genetic variation in populations

• For evolution to occur, individuals within a population must differ genetically

• Individuals within a population are more closely related to each other than members of other populations

What happens when individuals on the same species are isolated from each other?

Different populations of the same species may be isolated from each other such that gene flow is rare

What is the gene pool?

• The sum of all alleles at all gene loci in all individuals within a population

• Characterizes a population’s genetic makeup

• Used to identify the genotypes and calculate genotype frequencies

How will variation be inherited?

variation that can be inherited and is best suited for environment will be disproportionately passed to the next generation

What is environmental variation?

variation among individuals due to different enviroments

What is genetic variation?

difference in genetic material that is transmitted to offspring

How does genetic variation impact physical differences?

difference in DNA —> difference in RNA and proteins —> affects molecular formation of cell —> lead to physical difference we can observe

What causes variation in sexual organisms?

fertilizations = unique combinations of genes

What is evolutionary theory?

• predicts new species arise by divergence of populations through time from a common ancestor

• closely related species look like each other more than distant relatives

What is the tree of life?

full set of evolutionary relationships

What are the major parts of the three of life?

• Two major branches

  • bacteria

  • Archaea and Eukarya

  • most plants and animals are only two branches in Eukarya

What are most branches on the tree of life?

Microorganisms

What is represented at the root of the tree of life?

The last common ancestor of all organisms

Evidence of evolutionary theory

• nested patterns and succession of fossils in geological records

How to alleles interact with phenotype?

• offspring inherit one allele from each parent (two alleles total)

• allele in same location in chromosome determine observable trait

Species definition?

group of individuals capable, through reproduction, of sharing alleles with one another

what do individuals in species represent?

Individuals represent different combinations of alleles drawn from the species gene pool.

What are somatic mutations?

• occurs in body tissue nonreproductive cells

• only affects cells descended from one cell where mutation originally rose —> affects only that one individual

What are neutral mutations?

• have little to no effect

• silent mutation that does not alter amino acids

• or amino acid change but no change to protein function

What are deleterious mutations?

• harmful effect on organisms

• large portion of mutations that occur in protein-coding regions of genome

What are advantageous mutations?

• improve chances of survival and reproduction

• results in species adapting to environment

What is the most rare mutation?

Advantageous mutations

What can happen to the population with advantageous mutations?

• can increase in frequency in population until carried by every member of spices (fixation)

What is the best qualitative variation?

• Ladybugs —> two distinct states

• B and C= quantitative variations (range)