Biology Gre Vocabulary

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heterozygous advantage

Back 1

survival advantage that heterozygotes for a disease gene have over either the homozygous dominant (normal) or homozygous recessive (diseased) population

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histones

Back 2

proteins associated with DNA in eukaryotic chromosomes

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home range

Back 3

area an animal utilizes during its routine activities; may overlap with home ranges of other animals; is not defended

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hydrostatic skeleton

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a support system composed of fluid held in a closed body compartment under pressure; used by worms and jellyfish

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intron

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segments of gene that are transcribed, but subsequently excised from mRNA

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juvenile hormone

Back 6

insect hormone responsible for developmental staging

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kinetochore microtubules

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spindle microtubules that connect to the centromeres of chromosomes during mitosis

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k-selected species

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a species whose population levels off at the carrying capacity of the environment

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lamellipodia

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narrow extensions of the plasma membrane, pushed up by actin polymerization, found at the leading edge of a crawling cell
lampbrush chromosome

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lampbrush chromosome

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found especially in amphibian oocytes; chromosome in diplotene stage of first meiotic division characterized by paired lateral loops

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lenticels

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spongy areas in the bark of woody plants that allow for gas exchange

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limiting factors

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necessary substances found in short supply that, because of their short supply, limit an orgainism's growth

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linker DNA

Back 13

DNA that connects nucleosomes (octamers of histones with associated DNA)

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meristematic tissue

Back 14

embryonic plant tissue that allows for growth

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monophyletic species

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derive from one common ancestor

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mutation

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heritable change in sequence of genomic DNA

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niche

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an organism's potential use of biotic and abiotic factors in its environment

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nondisjuction

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failure of chromosomes to separate properly in anaphase I or anaphase II of meiosis, resulting in an unequal distribution of chromosomes in the gametes

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oncogenes

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normal vertebrate genes involved in regulation of growth that may lead to neoplastic transformation if overexpressed or mutated

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operon

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group of adjacent coregulated genes

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optimality theory

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only most beneficial of all possible beneficial phenotypes prevail in gene pool

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peptidoglycan

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material of bacterial cell walls

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petiole

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the stem of a leaf that connects it to the main stem of the plant

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phloem

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the part of the vascular system of a plant that transports sugars and other nutrients

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phylogeny

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relates to the evolutionary history of a species

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phylogenetic species

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derive from more than one ancestor

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pith

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the core of the central root of monocots

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pleiotrophic genes

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exert an effect on more than one trait

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polar microtubules

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spindle microtubules that do not connect to chromosomes during mitosis; they push against each other to elongate the cell

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polytene chromosomes

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giant chromosomes formed by excessive replication of DNA without subsequent mitosis and cytokinesis; they have a characteristic banding pattern

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promoter

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DNA site for RNA polymerase to initiate transcription

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pseudogenes

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DNA sequences that appear to be once functional genes that acquired mutations during evolution rendering them nonfunctional

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regulatory genes

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genes that encode proteins that regulate other genes

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resting potential

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-70 mV (i.e., electrical potential of nerve cell membrance in resting state)

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reverse transcriptase

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DNA polymerase that uses RNA as a template; used by retroviruses to create a DNA version of their RNA genome for insertion into the genome of their host cell

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RNA polymerase

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RNA transcription enzyme utilizing DNA template

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R-selected species

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a species whose population has periodic rises and falls; an unstable population size

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ruffled edge

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the leading edge of a crawling cell; the lamellipodia sweep back as the cell moves forward, giving the edge a "ruffled" look

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stabilizing selection

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intermediate variants of a distribution of phenotypes favored over extreme variants; occurs in stable populations

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synapsis

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pairing of homologous chromosomes during meiosis

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telomere

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repetitive sequences of DNA found at the ends of chromosomes

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territory

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area that an animal defends against intruders

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thermocline

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terperature gradient of more than one degree celsius per meter (i.e., as occurs in lakes in the summer)

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translocation

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exchange of chromosomal material between nonhomologous chromosomes

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transposons

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a mobile section of DNA that promotes genetic variability

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tubulin

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the helical protein that forms microtubules

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vegetal pole

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the pole of an egg with the greater amount of yolk; found opposite the animal pole

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vinculin

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one of several different proteins involved in cell adhesion

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vitelline layer

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a clear layer on the outside of oocyte plasma membranes; separates from the oocyte membrane after fertilization during the cortical reaction

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xylem

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the part of the vascular system of a plant that transports water

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zwitterion

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an amino acid with equal number of negative and positive charges; electrically neutral