Organic Evolution Exam 1

Information taken from PowerPoints and readings. Vocab and summary information

Evolution

Evolution

The change in frequency of heritable traits of a population over time

Lamarck’s Transmutation Theory

First theory of transmutation. Consisting of the complexifying force and the adaptive force

Complexifying force

Organisms move toward “ever greater perfection” i.e. vertebrates, humans

Adaptive force

2 rules by which species adapt to their environments:

1) Use and disuse: if a part or trait is used, it will enlarge or improve

2) Inheritance of acquired characteristics: once a trait is modified, this modification is inherited in the next generation

Malthusian Crunch/Catastrophe

When population growth outpaces subsistence availability, causing famine or war, resulting in poverty and depopulation.

Carrying Capacity

Resource limitation (food, space) that sets the absolute upper bound of population size

Density-dependent factors

Disease, competition, predation, etc.

Density-independent factors

Storms, volcanoes, droughts, fires, etc.

Adaption via natural selection

1) Variation: all populations of an organism vary

2) Inheritance: offspring inherit phenotypic traits from their parents

3) Differential reproductive success: some variants, those best adapted to their environments, leave more offspring than others

The Darwinian Revolution

• All living beings are connected by common ancestry

• Major mechanism of change is natural selection, with no conscious designer

• Humans are not special creations

• Variation is the norm

Blending Inheritance

The dominant theory of inheritance at the time of publishing The Origin. Offspring of two phenotypes are expected to display an intermediate phenotype

Genetic Swamping Argument

Proposed by Fleeming Jenkin in 1867: argued that (1) a new species (sport) is rare, and (2) even if the sport had an advantage, the trait would be lost over generations as it was swamped by the wildtype via blending

Blending results in 50% of variation being lost with each generation.

Darwin’s Theory of Pangenesis

A quick solution theory of particulate inheritance to resist the genetic swamping argument: information from different parts of the body is sent to the reproductive system via gemmules, enabling inheritance of acquired characters. Gemmules had affinity for each other and aggregated into the sexual elements/buds.

Weismann’s Germ Plasm Theory

Very early on in the development of animals, the germ line is set aside from the rest of the animal (soma). No inheritance of acquired characters—deviations in soma give rise to temporary non-hereditary variations. Called the Weisman barrier

Hugo De Vries

Tested Darwin’s pangenesis theory by breeding plants: noticed a reproducible 3:1 ratio, determined that tiny material elements are being inherited unchanged (called them pangenes). Identified unique bud sport of primrose, calling it a mutation.

RA Fisher

A biological mathematician who resolved conflict between Mendelians and Biometricians, showing that Mendelian inheritance proves natural selection.

Hardy-Weinberg Equation

p²+2pq+q²

p = frequency of allele A

q = frequency of allele B

Hardy-Weinberg Equillibrium

A state in which a population of organisms is not evolving (i.e. allele frequencies are not changing from generation to generation). Must meet these requirements:

• No non-random mating

• No natural selection

• No genetic drift (random variation)

• No immigration or emigration

• No mutation

De Vries’ Theory of Mutationism

New species are created in a single macromutation, natural selection only acts to destroy the most harmful mutations

The Genetic Code

Triplet codons are translated to amino acids in proteins, or are messages to stop translation

Types of mutations

1) Point Mutations

Silent, Nonsense (change of protein length), Missense (change of amino acid)

2) Indel mutations

Insertions or deletions (can shift reading frame)

Mc1r Gene

Located in chromosome #16. Codes for MC1R receptor protein that helps stimulate genes involved in the synthesis of eumelanin. A cytosine → thymine mutation at position 199 changes arginine → cystine, a missense mutation creating lighter coat color in mice.

Light colored mice have a repressed receptor on the Mc1r gene.

CCR5-delta32 Mutation

Deletion of 32 bp of CCR5 receptor. 2 copies of this alleles results in HIV immunity, because CCR5 is a one receptor that enables the HIV virus to enter helper T cells.

Gene duplication

Occurs when a mutation (ex. ectopic recombination) accidentally copies a gene, resulting in 2 identical copies. Serves as raw material: mutations to one of the copied genes won’t affect phenotype, so copy genes can act as origins of novelty.

• Created cone snail venom toxins, antifreeze glycoproteins in fish

Lederberg & Lederberg Experiment

Demonstrated that mutations are random: bacteria that survived antibiotic treatment had preexisting antibiotic resistance that was selected for.

Parthenogenesis

Asexual reproduction that involves the development of a female gamete without fertilization

Weismann’s Diversity Hypothesis

Sex exists because it generates diversity that is critical for adaptation, that outweighs the cost of sexual reproduction

Muller’s Ratchet

Sex purges the genome of deleterious mutations that would otherwise accumulate in asexual genomes; allows repairs of mutation via copy from wildtype alleles.

Proved by Graham Bell when he made protozoans sad by making them virgins

Red Queen Hypothesis

Genetic diversity generated by sex helps protect against parasitic infection

Permanent linkage

Beneficial and deleterious alleles cannot be unlinked from one another: entire genomes must be the smallest units of selection

Crossing over

Discovered by Thomas Morgan: traits can become unlinked due to genetic recombination during sexual reproduction

Can also happen in the middle of a gene to create a novel allele (raw material)

Ruby-in-the-Rubbish effect

via sexual recombination, individual alleles can be sorted, allowing individual alleles to contribute to fitness

In yeast, sexual populations are able increase frequency of beneficial alleles and decrease frequency of deleterious alleles. Asexual populations must increase both

Gene flow

Sex enables alleles to be changed between populations, can enable adaption (ex. EPAS1 gene passed from Denisovans to Tibetans)

Benefits of sex

• Lose the bad: eliminate negative mutations (rachet) and alleles (ruby-in-the-rubbish)

• Gain the good: obtain beneficial alleles from crossover and gene flow

• Arms race: help to battle with parasites (Red queen hypothesis)

Horizontal Gene Transfer (HGT)

Gene transfer that occurs between living beings of the same species or different species, without transfer via reproduction

Can be adaptive in the same way that gene flow can lend adaptive genes to different populations. Plays a large part in antibiotic resistance

Syncytin

A virus-originating gene encoding a protein made only by cells in the placenta that enables placenta cells to fuse together to create the syncytiotrophoblast

Transferred at least six times into mammalian lineages: placental fusion is more efficient with syncytin than with mammalian genes

Bdelloid rotifers

Group of animals that have been asexual for 80 mya

Transposons

Segments of DNA that can move around to different positions in the genome of a single cell (‘jumping genes’), discovered by McClintock

Agouti Mice

When a retrotransposon inserts near the coding side of the agouti gene, the agouti gene’s expression is disrupted and codes for yellow pigmentation (and obesity)

Transposons and Pregnancy

Mammalian genomes have ‘tamed’ transposon start site fragments to remaining next to hundreds of progesterone responsive genes, without the transposition ability. Enables the coordination of bodily functions during pregnancy

Symbiogenesis

Lynn Margulis’ idea that symbiosis was the driving force of evolution, after hypothesizing the theory of endosymbiosis

Endosymbiosis

Mitochondria formed after a prokaryote that had evolved into an early eukaryote engulfed and kept one or more proteobacteria cells.

Microbiome

The ecosystem of microbes inside/outside of animal bodies and guts. Microbial genes outnumber human genes 100:1.

Help to digest food, build essential nutrients, and defend against bacterial infections

Microbiome and HGT

Gut bacterium Bacteroides plebius contains the same gene as in Japanese people due to symbiosis in digesting seaweed. People can pass on bacterium and bacterium genes to offspring—heritable trait!

Origins of Variation

• HGT: adaptive genes can be transferred among organisms, especially bacteria

• Transposons: jumping genes can sometimes jump into a spot that is beneficial, especially in regulatory regions

• Mutualism: organisms can acquire variations by associating with other organisms that possess those variations