BSC2011 Final Exam

Zygote

A diploid cell resulting from the fusion of two haploid gametes; a fertilized ovum.

Cleavage

A period of rapid cell division without growth following fertilization.

Blastula

A hollow ball of cells marking the end stage of cleavage during early embryonic development.

Gastrulation

The process where the blastula folds inward, forming the three germ layers.

Germ Layers

The three layers (Ectoderm, Mesoderm, Endoderm) that give rise to all tissues and organs.

Organogenesis

The stage of development where the germ layers begin to develop into organs.

Cytoplasmic Determinants

Maternal substances in the egg that influence the course of early development.

Induction

A process where one group of cells influences the development of neighboring cells via chemical signals.

Cell Differentiation

The process by which cells become specialized in structure and function.

Totipotency

The ability of a single cell to divide and produce all the differentiated cells in an organism.

Genomic Equivalence

The concept that all cells in an organism contain the same genes.

Hox Genes

A group of homeotic genes that control the body plan of an embryo along the head-to-tail axis.

Bindin Proteins

Proteins on the surface of sperm that ensure species-specific recognition of the egg.

Acrosomal Reaction

The discharge of enzymes from the tip of the sperm that helps it penetrate the egg.

Morphogenesis

The physical process that gives an organism its shape.

Allele

Alternative versions of a gene (e.g., dominant vs. recessive).

Genotype vs. Phenotype

Genotype is the genetic makeup (Aa); Phenotype is the physical appearance (Blue eyes).

Homozygous vs. Heterozygous

Homozygous has two identical alleles (AA); Heterozygous has two different alleles (Aa).

Law of Segregation

Mendel's law stating that two alleles for a heritable character separate during gamete formation.

Law of Independent Assortment

Genes for different traits can segregate independently during the formation of gametes.

Mitosis vs. Meiosis

Mitosis produces 2 identical diploid cells; Meiosis produces 4 unique haploid gametes.

Sister Chromatids

Identical copies of a chromosome joined together by a centromere.

Homologous Chromosomes

A pair of chromosomes (one from each parent) that carry the same genes at the same loci.

Incomplete Dominance

A pattern where the phenotype of the heterozygote is an intermediate blend (e.g., Pink flowers).

Codominance

A pattern where both alleles are fully expressed (e.g., Blood type AB).

Sex-Linked Traits

Traits located on the sex chromosomes (usually the X), showing different inheritance patterns in males and females.

Epistasis

A phenomenon where one gene alters the phenotypic expression of a second gene.

Polygenic Inheritance

An additive effect of two or more genes on a single phenotypic character (e.g., skin color).

Tumor Suppressor Genes

Genes (like p53) that normally help prevent uncontrolled cell growth.

Aneuploidy

A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number.

Natural Selection

The process by which individuals with certain inherited traits tend to survive and reproduce at higher rates.

Mutation

A change in the nucleotide sequence of an organism's DNA; the ultimate source of genetic variation.

Gene Pool

The aggregate of all copies of every type of allele at all loci in every individual in a population.

Allele Frequency

The proportion of a specific allele relative to the total number of alleles in a population.

Genetic Drift

Unpredictable fluctuations in allele frequencies from one generation to the next due to chance (small populations).

Founder Effect

Genetic drift that occurs when a few individuals become isolated from a larger population.

Bottleneck Effect

Genetic drift that occurs when the size of a population is sharply reduced by a natural disaster.

Gene Flow

The transfer of alleles into or out of a population due to the movement of fertile individuals or gametes.

Hardy-Weinberg Equilibrium

The condition in which a population's allele frequencies remain constant over generations (non-evolving).

Paradox of Variation

The observation that populations maintain high levels of genetic variation despite natural selection.

Heterozygote Advantage

Greater reproductive success of heterozygous individuals compared to homozygotes (e.g., Sickle-cell trait).

Reproductive Isolation

The existence of biological barriers that prevent members of two species from interbreeding.

Speciation

The process by which one species splits into two or more species.

Microevolution

Evolutionary change below the species level; change in the allele frequencies in a population over generations.

Species Richness

The number of different species in a biological community.

Species Evenness

The relative abundance of each species in a community.

Competitive Exclusion

The concept that two species competing for the same limiting resource cannot coexist permanently.

Niche Partitioning

The differentiation of niches that enables similar species to coexist in a community.

Character Displacement

The tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations.

Mutualism

A symbiotic relationship in which both participants benefit (+/+).

Commensalism

A relationship between species in which one benefits and the other is neither harmed nor helped (+/0).

Trophic Levels

The hierarchical levels in an ecosystem, comprising organisms that share the same function in the food chain.

Primary Production

The amount of light energy converted to chemical energy by autotrophs during a given time period.

Energy Flow (10% Rule)

Only about 10% of energy is transferred from one trophic level to the next.

Biomes

Major life zones characterized by vegetation type or physical environment.

Ecosystem Services

Functions performed by an ecosystem that directly or indirectly benefit humans (e.g., nutrient cycling).

Steward’s Carrot Experiment

Cultured single phloem cells from carrot roots in a nutrient medium; cells developed into full, fertile plants; concluded that differentiated plant cells are totipotent and retain all genetic info; totipotency, differentiation, genomic equivalence; 1950s.

Gurdon’s Nuclear Transplantation

Replaced frog egg nuclei with nuclei from older tadpole cells; younger nuclei produced normal embryos while older nuclei rarely did; concluded that cell potential decreases as differentiation progresses but the full genome is still present; nuclear transplantation, genomic equivalence, frog; 1960s.

Dolly the Sheep

Fused an enucleated egg with a differentiated mammary gland cell from an adult sheep; a viable clone (Dolly) was born; proved that adult mammal cells can be "reprogrammed" to be totipotent; reproductive cloning, differentiation, mammary cell; 1996.

Bicoid in Fruit Flies

Analyzed Drosophila embryos with mutated bicoid genes; embryos lacked heads and developed two tails; concluded that bicoid is a maternal effect gene/morphogen that establishes the anterior-posterior axis; cytoplasmic determinants, morphogen, anterior; 1980s.

Hans Spemann (1938)

Divided salamander eggs with a hair loop to ensure only one half received the "gray crescent"; only the side with the gray crescent developed into a normal embryo; concluded that the gray crescent contains essential cytoplasmic determinants; gray crescent, salamander, determinants; 1938.

Spemann and Mangold (1924)

Transplanted the dorsal lip of a blastopore to the ventral side of a different gastrula; a second embryo (conjoined twin) formed at the site; concluded the dorsal lip acts as an "organizer" that induces development; induction, Spemann organizer, gastrulation; 1924.

Mendel’s Monohybrid and Dihybrid Crosses

Tracked specific traits in pea plants over multiple generations; observed consistent 3

Kettlewell (1950)

Released light and dark moths into polluted and unpolluted forests to track survival; dark moths survived better in polluted woods due to bird predation; provided direct evidence of natural selection in response to environmental change; natural selection, industrial melanism, adaptation; 1950s.

Andersson (1982)

Manipulated male widowbird tail lengths (shortened vs. lengthened) and counted nests; males with artificially lengthened tails attracted significantly more mates; concluded that female choice (sexual selection) can drive the evolution of exaggerated traits; sexual selection, female choice, widowbird; 1982.

Tree Hole Study

Manipulated the amount of leaf litter (energy) entering tree hole ecosystems; lower energy input resulted in shorter food chains; supported the Energetic Hypothesis that energy transfer efficiency limits food chain length; energetic hypothesis, food chain, trophic levels; 1990s.

Robert Paine’s Sea Star Study

Removed the predatory sea star Pisaster from intertidal plots; mussel populations exploded and species richness dropped from 15 to 8; concluded that keystone species maintain community diversity by preventing dominant competitors; keystone species, species richness, intertidal; 1966.

C. B. Huffaker’s Oranges

Created simple and complex orange-tray environments for predator and prey mites; simple setups led to extinction; complex setups with barriers allowed for stable oscillations; concluded that environmental complexity and refuges allow predator-prey coexistence; predator-prey, environmental complexity, refuges; 1958.

Competition between Paramecium (Gause)

Grew two species of Paramecium together in a culture with a single resource; one species consistently outcompeted the other to extinction; defined the Competitive Exclusion Principle; competitive exclusion, niche, resource competition; 1934.

Connell’s Barnacles

Removed the barnacle Balanus from rocks to see the effect on Chthamalus; Chthamalus expanded its range into the lower zone; concluded that competition restricts a species to a realized niche that is smaller than its fundamental niche; fundamental vs realized niche, competition, zonation; 1961.