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Chapter 12-15

Biology Key Terms

Gonads Sex organs: ovaries in females, testes in males.
Autosomes Paired chromosomes present in both males and females; all chromosomes except the X and Y chromosomes.
Sex Chromosomes Paired chromosomes that differ between males and females, XX in females, XY in male.
X-Linked Trait A phenotype determined by an allele on an X chromosome.
Pedigree A visual representation of the occurrence of phenotype across generations.
Y-Chromosome Analysis Comparing sequences on the Y chromosomes to examine paternity and paternal ancestry.
Incomplete Dominance A form of inheritance in which heterozygotes have a phenotype that is intermediate between homozygous dominant and homozygous recessive.
Codominance A form of inheritance in which both alleles contribute equally to the phenotype.
Continuous Variation Variation in a population showing an unbroken range of phenotypes rather than discrete categories.
Polygenic Trait A trait whose phenotype is determined by the interaction among alleles of more than one gene.
Multifactorial Inheritance An interaction between genes and the environment that contributes to a phenotype or trait.
Aneuploidy An abnormal number of one or more chromosomes (either extra or missing copies).
Nondisjunction The failure of chromosomes to separate accurately during cell division; nondisjunction in meiosis leads to aneuploidy gametes.
Trisomy 21 Carrying an extra copy of chromosome 21; also known as Down syndrome.
Amniocentesis A procedure that removes fluid surrounding the fetus to obtain and analyze fetal cells to diagnose genetic disorders.
Karyotype The chromosomal makeup of cells. Karyotype analysis can be used to detect trisomy 21 prenatally.
Stem Cells Immature cells that can divide and differentiate into specialized cell types.
Tissue An organized group of different cell types that work together to carry out a particular function.
Adult (Somatic) Stem Cells Stem cells located in tissues that help maintain and regenerate those tissues.
Cellular Differentiation The process by which a cell specializes to carry out a specific role.
Differential Gene Expression The process by which genes are "turned on," or expressed, in different cell types.
Multipotent Describes a cell with the ability to differentiate into a limited number of cell types in the body.
Embryonic Stem Cells Stem cells that make up an early embryo and which can differentiate into nearly every cell type in the body.
Blastocyst The stage of embryonic development in which the embryo is a hollow ball of cells. Researchers can derive embryonic stem cell lines during the blastocyst stage.
Pluripotent Describes a cell with the ability to differentiate into nearly any cell type in the body.
Totipotent Describes a cell with the ability to differentiate into any cell type in the body.
Induced Pluripotent Stem Cell A pluripotent stem cell that was generated by manipulation of a differentiated somatic cell.
Antibiotics Chemicals that either kill bacteria or slow their growth by interfering with the function of essential bacterial cell structures.
Binary Fission A type of asexual reproduction in which one parental cell divides into two.
Population A group of organisms of the same species living together in the same geographic area.
Evolution Change in allele frequencies in a population over time.
Fitness The relative ability of an organism to survive and reproduce in a particular environment.
Natural Selection Differential survival and reproduction of individuals in response to environmental pressure that leads to change in allele frequencies in a population over time.
Adaptation The process by which populations become better suited to their environment as a result of natural selection.
Directional Selection A type of natural selection in which organisms with phenotypes at one end of a spectrum are favored by the environment.
Stabilizing Selection A type of natural selection in which organisms near the middle of the phenotypic range of variation are favored by the environment.
Diversifying Selection A type of natural selection in which organisms with phenotypes at both extremes of the phenotypic range are favored by the environment.
Population Genetics The study of the genetic makeup of populations and how the genetic composition of a population changes.
Gene Pool The total collection of alleles in a population.
Allele Frequency The relative proportion of an allele in a population.
Nonadaptive Evolution Any change in allele frequency that does not by itself lead a population to become more adapted to its environment; the causes of nonadaptive evolution are mutation, genetic drift, and gene flow.
Genetic Drift Random changes in the allele frequencies of a population between generations; genetic drift tends to have more dramatic effects in smaller populations than in larger ones.
Founder Effect A type of genetic drift in which a small number of individuals leaves one population and establishes a new population; by chance, the newly established population may have lower genetic diversity than the original population.
Bottleneck A type of genetic drift that occurs when a population is suddenly reduced to a small number of individuals, and alleles are lost from the population as a result.
Gene Flow The movement of alleles from one population to another, which may increase the genetic diversity of a population.
Inbreeding Mating between closely related individuals. Inbreeding does not change the allele frequency within a population, but it does increase the proportion of homozygous individuals to heterozygotes.
Inbreeding Depression The negative reproductive consequences for a population associated with having a high frequency of homozygous individuals possessing harmful recessive alleles.
Hardy-Weinberg Equilibrium The principle that, in a nonevolving population, both allele and genotype frequencies remain constant from one generation to the next.
Hardy-Weinberg Equation A mathematical formula that calculates the frequency of genotypes and phenotypes one would expect to find in a nonevolving population.
Biological Species Concept The definition of a species as a population whose members can interbreed to produce fertile offspring.
Reproductive Isolation Mechanisms that prevent mating (and therefor gene flow) between members of different species.
Speciation The genetic divergence of populations, leading over time to reproductive isolation and the formation of new species.
Created by: tblackdog