Flahs Cards IV
chapter four flash cards
Terms
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- locus
- the position on a chromosome where a given gene occurs. the term is sometimes used interchangeably with gene, but this usage is technically incorrect
- principle of segregation
- genes (alleles) occur in pairs (because chromosomes occur in pairs). during gamete production, the members of each gene pair separate, so that each gamete contains one member of each pair. during fertilization, the full number of chromosomes is restored, and members of gene or allele pairs are reunited
- random assortment
- the chance distribution of chromosomes to daughter cells during meiosis; along with recombination, a source of variation resulting from meiosis
- phenotypes
- the observable or detectable physical characteristics of an organism; the detectable expressions of genotypes
- recessive
- describing a trait that isn't expressed in heterozygotes; also refers to the allele that governs the trait. for a recessive allele to be expressed, there must be two copies of it (i.e. the individual must be homozygous)
- genetic drift
- evolutionary changes - that is, changes in allele frequencies- produced by random factors. genetic drift is a result of small population size
- polygenic
- referring to traits that are influenced by genes at two or more loci. Examples of such traits are stature, skin color, and eye color. Many polygenic traits are also influenced by environmental factors
- principle of independent assortment
- the distribution of one pair of alleles into gametes does not influence the distribution of another pair. The genes controlling different traits are inherited independently of one another
- Mendelian traits
- characteristics that are influenced by alleles at only one genetic locus. examples include many bloody types, such as ABO. Many genetic disorders, including sickle cell anemia and tay-sachs disease are also mendelian traits
- heterozygous
- having different alleles at the same locus on members of a chromosome pair
- sickle-cell anemia
- a severe inherited hemoglobin disorder in which red blood cells collapse when deprived of oxygen. it results from inheriting two copies of mutant alleles. this mutation is cuased by a single base substitution in the DNA
- macroevolution
- large-scale changes that occur in populations after many generations, such as the apperance of a new species (speciation)
- directional change
- in a genetic sense, the nonrandom change in allele frequencies caused by natural selection. the change is directional because the frequencies of alleles consistently increase or decrease (they change in one direction), depending on environmental circumstances and the selective pressures involved
- homozygous
- having the same allele at the same locus on both members of a chromosome pair
- dominant
- describing a trait governed by an allele that can be expressed in the presence of another, different allele (i.e. in heterozygotes). Dominant alleles prevent the expression of recessive alleles in heterozygotes. (this is the definition of complete dominance)
- hybrids
- Offspring of parents who differ from one another with regard to certain traits or certain aspects of genetic makeup; heterozygotes
- microevolution
- small genetic changes that occur within a species. A human example is the variation seen in the different ABO blood types
- antigens
- large molecules found on the surface of cells. several different loci govern various antigens on red and white blood cells
- gene pool
- the total complement of genes shared by the reproductive members of a population
- genotype
- the genetic makeup of an individual. Genotype can refer to an organisms entire genetic makeup or to the alleles at a particular locus
- variation (genetic)
- inherited differences among individuals; the basis of all evolutionary change
- allele frequency
- in a population, the percentage of all the alleles at a locus accounted for by one specific allele
- codominance
- the expression of two alleles in heterozygotes. in this situation, neither allele is dominant or recessive; thus both influence the phenotype
- founder effect
- a type of genetic drift in which allele frequencies are altered in small populations that are take from, or are remnants of larger populations
- population
- within a species a community of individuals where mates are usually found
- alleles
- alternate forms of genes. alleles occur at the same locus on partner chromosomes and thus govern the same trait. however, because they are slightly different, their action may result in different expressions of that trait. The term is sometimes used synonymously with gene