Genetic and Evolution

locus

specific location on a chromosome

allele

alternate form a gene

genotype

genetic combination possessed by an individual

phenotype

physical appearance from a given genotype

dominant

only one copy of an allele is needed to express a given phenotype

recessive

two copies of an allele are needed to express a phenotype

homozygous

both alleles are the same

heterozygous

both alleles are different

complete dominance

only one dominant and one recessive allele exist for a given gene

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presence of one dominant allele masks the recessive allele

codominance

more than one dominant allele exists for a given gene

incomplete dominance

occurs when a heterozygote expresses a phenotype that is intermediate between the two homozygous genotypes

penetrance

population measure defined as the proportion of individuals in the population carrying the allele who actually express the phenotype

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population parameter

expressivity

varying phenotypes despite identical genotypes

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considered at the individual level; reflects the gray area in expression

constant expressivity

all individuals with a given genotype express the same phenotype

variable expressivity

individuals with the same genotype may have different phenotypes

Law of Segregation

1. genes express in alternate forms (alleles)
2. an organism has two alleles for each gene; one inherited from each parent
3. two alleles segregate during meiosis, resulting in gametes that carry only one allele for any inherited trait
4. if two alleles of an organism are different, only one will be fully expressed and the other will be silenced


1. expressed allele = DOMINANT
2. silent allele = SILENT

Law of Independent Assortment

inheritance of one gene does not affect the inheritance of another gene

recombination

genetics refers to the process by which genetic material, typically DNA, is shuffled or exchanged between two or more chromosomes during the formation of gametes (sperm and egg cells) or during certain phases of cell division, like meiosis. This process results in the creation of offspring with combinations of genetic traits that are different from those of their parents.

Frederick Griffith Experiment

a seminal experiment conducted in 1928 that provided important insights into the nature of bacterial transformation and the role of genetic material in inheritance. The experiment was a significant precursor to the later work that established DNA as the genetic material.

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Griffith worked with two strains of the bacterium Streptococcus pneumoniae: a "smooth" (S) strain that had a protective capsule and caused disease, and a "rough" (R) strain that lacked the capsule and was nonpathogenic.

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Results suggested that genetic material could be transferred between bacterial cells, leading to changes in their traits and behaviors

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laid foundation for the **transforming principle**

Hershey and Chase experiment

experiment that worked to confirm the idea that DNA could independently carry genetic information

epigenetics

term for changes in DNA that do not involve an alteration to the nucleotide sequence

imprinting

epigenetic process in which gene expression is determined by the contributing parent

gene pool

all the alleles that exist within a species

mutation

change in DNA sequence, and results in a mutant allele

wild-type

alleles that are considered “normal” and are ubiquitous in the study population

mutagen

substances that can cause mutations

transposons

elements that can insert and remove themselves from the genome

point mutation

silent mutation

occur when the change in nucleotide has no effect on the final protein synthesized from the gene

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most commonly occurs when the changed nucleotide is transcribed to be the third nucleotide in a codon because there is **degeneracy (wobble)** in the genetic code

missense mutation

occurs when the change in the nucleotide results in substituting one amino acid for another in the final protein

nonsense mutation

occurs when the change in nucleotide results in substituting a **stop codon** for an amino acid in the final protein

frameshift mutation

occur when the nucleotides are inserted into or deleted for the genome

chromosomal mutation

larger-scale mutations in which large segments of DNA are affected

deletion mutation

occurs when a large segment of DNA is lost from a chromosome; small deletions are considered frameshift mutations

duplication mutations

occurs when a segment of DNA is copied multiple times in the genome

inversion mutation

occur when a segment if DNA is reversed within the chromosome

insertion mutation

occur when a segment of DNA is moved from one chromosome to another; small insertions are considered frameshift mutations

translocation mutation

occur when a segment of DNA from one chromosome is swapped with a segment of DNA from another chromosome

hybrid

individuals form different but closely related species mate to reproduce

genetic drift

changes in the composition of the gene pool due to chance

founder effect

more extreme case of genetic drift in which a small population of a species finds itself in reproductive isolation from other populations as a result of natural barriers, catastrophic events, or other **bottlenecks** that drastically and suddenly reduce the size of the population available for breeding

inbreeding

mating between two genetically related individuals

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encourages homozygosity, which increases the prevalence of both homozygous dominant and recessive genotypes

inbreeding depression

reduced fitness of a population

outbreeding/outcrossing

introduction of unrelated individuals into a breeding group

recombination frequency

proportional to the distance between the genes on the chromosome

Hardy-Weinberg Equilibirum

1. population is very large (no genetic drift)
2. no mutations that affect the gene pool
3. mating between individuals in the population is random (no sexual selection)
4. no migration of individuals into or out of the population
5. genes in the population are all equally successful at being reproduced

Hardy-Weinberg Principle

p + q = 1

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p^2 + 2pq + q^2 = 1

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p^2 = frequency of homozygous dominant

q^2 = frequency of homozygous recessive

2pq = frequency of heterozygous dominant

natural selection

1. organisms produce offspring, few of which survive to reproductive maturity
2. chance variation within individuals in a population may be heritable. If these variations give an organism even a slight survival advantage, the variation is termed favorable
3. individuals with greater **fitness** survive

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modern synthetic model/neo-darwinism

theoretical framework in evolutionary biology that combines Charles Darwin's theory of natural selection with Gregor Mendel's ideas about genetics. It emerged in the early 20th century and represents a significant advancement in our understanding of how evolution works

inclusive fitness

measure of an organism’s success in the population, based on the number of offspring, success in supporting offspring, and the ability of the offspring to then support others

punctuated equilibrium

suggests that changes in some species occur in rapid bursts rather than evenly over time

stabilizing selection

keeps phenotypes within a specific range by selecting against extremes

directional selection

adaptive pressure can lead to the emergence and dominance of an initially extreme phenotype

disruptive selection

two extreme phenotypes are selected over the norm

polymorphisms

naturally occurring differences in form between members of the same populationa

adaptive radiation

concept that describes the rapid rise of a number of different species from a common ancestor

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allows for various species to occupy different niches

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favored by environmental changes or isolation of small groups of the ancestral species

prezygotic mechanisms of isolation

prevent formation of the zygote

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**temporal isolation**: breeding at different times

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**ecological isolation**: living in different niches within the same territory

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**behavioral isolation**: lack of attraction between members of the two species due to differences in pheromones, courtship displays, etc.

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**reproductive isolation**: incompatibility of reproductive anatomy

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**game isolation**: intercourse can occur, but fertilization cannot

postzygotic mechanisms of isolation

allow for gamete fusion but yield either nonviable or sterile offspring

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**hybrid unviability**: formation of a zygote that cannot develop to term

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**hybrid breakdown**: forming a first-gen hybrid offspring that are viable and fertile, but 2nd-gen hybrid offspring that are inviable or infertile

divergent evolution

independent development of dissimilar characteristics in two or more lineages sharing a common ancestor

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Ex. seals and cats

parallel evolution

process whereby related species evolve in similar ways for a long period of time in response to analogous environmental selection pressures

convergent evolution

independent development of similar characteristics in tow or more lineages not sharing a recent common ancestor

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Ex. dolphins and fish