04 Genetics & Evolution

Fossil Record

The collection of fossils spanning the history of life on Earth

Biogeography

the study of organisms geographical distribution presently and through the history of life on Earth

Comparative Anatomy

study of anatomical structures and their evolutionary relatedness between species

Comparative Embryology

the study of the difference and similarities in embryological development between species

Homology

sharing a common ancestor

Convergent Evolution

the process by which unrelated or distantly related organisms evolve similar phenotypes or adaptations because they are under similar selective pressure

Analogous Structures

anatomical structures from different species which appear similar as a result of convergent evolution

Divergent Evolution

the process by which related organisms or those of the same species evolve differently in response to different selective pressures

Ribozyme

an RNA molecule that possesses catalytic functions like an enzyme

4.6 Billion Years Ago

the age of the Earth

3.8 Billion Years Ago

Approximate date of when life arose on Earth

2.8 Billion Years Ago

Approximate date of the evolution of photosynthesis

1.2 Billion Years Ago

Approximate date of the evolution of eukaryotic cells

500 Million Years Ago

Approximate date of the movement of multicellular organisms to terrestrial environments

200,000 Years Ago

Approximate date of the evolution of modern Homo sapiens

Species

a group of organisms who are able to produce fertile offspring together

Clade

All the species that share a common ancestor

Phylogenetic Tree

A branching diagram that shows the evolutionary relationships between various species

Prezygotic Barriers

conditions that occur before the formation of the zygote that promote genetic isolation of populations of a species

Postzygotic Barriers

mechanisms that reduce viability or reproductive capacity of hybrid organism

Natural Selection

The process by which organisms better adapted to their environment (i.e. higher fitness) tend to survive and produce more offspring.

Stabilizing Selection

The mode of natural selection seen in a stable environment, selecting for the average phenotype and against extreme phenotypes

Directional Selection

The mode of natural selection in which an extreme phenotype is favored over others, causing allele frequency to shift toward those of the favored phenotype

Diversifying Selection

The mode of natural selection in which those individuals with extreme phenotypes to reproduce more than those with average phenotypes; also known as disruptive selection

Genetic Drift

evolution due to random chance

Founder Effect

the reduced genetic diversity that results when a population is descended from a small number of colonizing ancestors

Bottleneck Effect

A sharp reduction in population size due to environmental events (earthquake, flood, disease, etc.) leaving reduced genetic diversity in the surviving population

Gene Flow

movement of genes between populations by individual emigration or immigration

Evolution

Genetic change in a population over time

Acclimation

Physiological change in an individual in response to environment

Adaptation

A structure or trait that increases evolutionary fitness in an individual

Selective Pressure

Conditions in an organisms environment that affect its ability to survive and reproduce, e.g. resource availability, climate, predators, etc.

Fitness

the ability to survive and reproduce in an environment, i.e. how well suited an individual is for its environment

Allele Frequency

the relative frequency of an allele in a population; usually expressed as a percentage e.g. 43% of the individuals in this population have the "f" allele at a particular locus

Gene Pool

All the genes and combinations of them in a given population

Incomplete Dominance

The relationship between alleles in which a heterozygous individual displays an intermediate phenotype between the phenotypes of the two homozygous individuals

Codominance

When two alleles are expressed simultaneously

Polygenic Inheritance

When more that one locus (many genes) contribute to one trait

Pleiotropy

When many traits are controlled by a single locus (gene)

Sex-linked genes

When the gene of interest is found on the sex chromosomes (X or Y)

Multifactorial Inheritance

When the ultimate phenotypic result of a gene is influenced by the environment that organism is in

Norm of Reaction

The range of phenotypic outputs from a gene that is subject to multifactorial inheritance

Mutation

a change in the DNA sequence

Gamete

A cell for sexual reproduction, e.g. sperm or egg

Allele

a version of a gene

Genotype

the genetic information of an organism

Phenotype

the physical manifestation of the information in an organisms genome

Locus/loci

the location on a chromosome of a gene

Homozygous

when a both copies of a gene are the same allele

Heterozygous

when an organisms possesses two different alleles of a gene

Dominant

an allele that is expressed phenotypically over other recessive alleles present

Recessive

an allele that is only expressed phenotypically if no dominant alleles are present

Test-cross

crossing an organism with a dominant phenotype with a recessive phenotype, and analyzing the offspring to determine the genotype of the dominant parent

Wild-type Allele

An allele that is the most common in a population

Monohybrid Cross

crossing two individuals for one trait of interest encoded by one locus/gene

Dihybrid Cross

crossing two individuals and for two traits of interested each encoded by separate non-linked locus/genes

Ploidy

the number of sets of chromosomes in an organism

Somatic Cells

"body cell"; any of the cells in an organism that are not reproductive cells

Germline Cells

a population of cells in an organism dedicated to producing gametes via meiosis

Meiosis

A type of cell division that results in daughter cells with half the ploidy of the original cell

Syngamy

Fusion of egg and sperm

Zygote

the cell that results from the fusion of egg and sperm

Crossing Over

the event that occurs during Prophase I, in which homologous chromosomes exchange pieces to create new combinations of alleles

Tetrad

The four chromatids from two homologous chromosomes paired up during prophase 1 for crossing over

Haploid

Having only one set of chromosomes (or 1 copy of each gene)

Diploid

Having two sets of chromosomes (or 2 copies of each gene)

Tetraploid

Having four sets of chromosomse (or 4 copies of each gene)

Gametic Life Cycle

The life cycle of organisms that produce gametes by meiosis, and those gametes fuse to form a zygote which develops into the next generation of the organism