Exam #3 Chapter 8

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Character

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-observable feature, or trait, of an organism, whether acquired or inherited.

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Trait

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a genetically determined characteristic.

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Heritable Traits

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is the proportion of observed differences on a trait among individuals of a population that are due to genetic differences

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True-breeding

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A kind of breeding in which the parents with a particular phenotype produce offspring only with the same phenotype.

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Parental Generation

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The generation of individuals of different genotypes that are mated, usually for scientific purposes, to produce hybrids.

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First Filial Generation (F1)

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comprised of offspring(s) resulting from a cross between strains of distinct genotypes.

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Second Filial Generation (F2)

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comprised of offspring(s) resulting from mating or genetically crossing two members of first filial generation.

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Monohybrid Cross

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genetic cross between homozygous individuals but with different alleles for a single gene locus of interest

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Recessive

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Of, or pertaining to, a gene (or allele) whose phenotypic expression is masked by a dominant gene (or allele).

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Dominant

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Of, or pertaining to) An allele or a gene that is expressed in an organism’s phenotype, masking the effect of the recessive allele or gene when present.

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Particulate Theory

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A theory formulated by Gregor Mendel based on his garden pea breeding experiments wherein he conjectures that discrete particles (now referred to asgenes) that determine phenotypes are passed on from parents to offspring across generations.

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Diploid

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A cell or an organism consisting of two sets of chromosomes: usually, one set from the mother and another set from the father. In a diploid state the haploid number is doubled, thus, this condition is also known as 2n.

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Haploid

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The number of chromosomes in a gamete of an organism, symbolized by n

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Gene

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The fundamental, physical, and functional unit of heredity.

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Alleles

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One member of a pair (or any of the series) of genes occupying a specific spot on a chromosome (called locus) that controls the same trait.

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Locus (Loci)

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The location of a gene (or of a significant sequence) on a chromosome, as in genetic locus.

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Homozygous

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Of, or pertaining to an individual (or a condition in a cell or an organism) containing two copies of the same allele for a particular trait located at similar positions (loci) on paired chromosomes.

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Heterozygous

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Of, or pertaining to an individual (or a condition in a cell or an organism) containing two different alleles for a particular trait.

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Genotype

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A set of alleles that determines the expression of a particular characteristic or trait (phenotype).

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Phenotype

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The expression of a particular trait, for example, skin color, height, behavior, etc., according to the individual’s genetic makeup and environment.

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Law of Segregation

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Gregor Mendel's law stating that paired alleles separate during gamete formation. Consequently, each gamete would contain only one copy of every paired unit factors.

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Punnett Square

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A tool that helps to show all possible allelic combinations of gametes in a cross of parents with known genotypes in order to predict the probability of their offspring possessing certain sets of alleles.

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Test Cross

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Crossing an organism with dominant genotype to a recessive homozygote for a specific phenotype in order to determine dominance/recessiveness of the unknowngenotype and the pattern of inheritance based on the phenotype of each progeny.

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Dihybrid Cross

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A genetic cross between individuals with different alleles for two gene loci of interest.

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Law of Independent Assortment

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Mendelian law stating that for every pair of unit factors, each of them would assort independently into the newly formed gametes.

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Recombinant

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A cell or an individual with a new combination of genes not found together in either parent, usually applied to linked genes.

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Multiplication Rule

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he multiplication of the human species by natural generation.

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Pedigree

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An ancestral line or chart depicting the lineage or descent of an individual.

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Mutations

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A permanent, heritable change in the nucleotide sequence in a gene or a chromosome; the process in which such a change occurs in a gene or in a chromosome.

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Wild-Type

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Polymorphic

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Occurring in many forms, e.g. social ants having many adult forms.

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Dominance Hierarchy

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a social situation in which one organism dominates all below it, the next all below it, and so on down to the organism dominated by all.

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Incomplete Dominance

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A kind of dominance occurring in heterozygotes in which the dominant allele is only partially expressed, and usually resulting in an offspring with an intermediate phenotype.

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Codominance

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A condition in which the alleles of a gene pair in a heterozygote are fully expressed thereby resulting in offspring with a phenotype that is neither dominant norrecessive.

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Pleiotropy

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The single gene controlling or influencing multiple (and possibly unrelated) phenotypic traits.

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Epistasis

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is the interaction between the genes at two or more loci, so that the phenotype differs from what would be expected if the loci were expressed independently.

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Hybrid Vigor

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Increased vigor or other superior qualities arising from the crossbreeding of genetically different plants or animals. Also calledheterosis.

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Quantitative Trait Loci

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A trait produced by the interaction and additive effects of quantitative genes.

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Recombinant Frequencies

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The frequency at which crossing over occurs between two chromosomal loci--the probability that two loci will become unlinked during meiosis

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Genetic Maps

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A list of ordered genetic loci for a particular genome.

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Map Units (Centimorgans)

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A unit of recombination frequency, implying distance along a chromosome.

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Sex Chromosomes

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A type of chromosome in the genome that is involved in the determination of the sex as well as the development of sexual characteristics in an organism. It occurs in pairs in somatic cells while singly in sex cells (gametes).

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Autosomes

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Any chromosome not considered as a sex chromosome, or is not involved in sex determination. It occurs in pairs in somatic cells and singly in sex cells (gametes).

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Sex-linked

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Pertaining to a gene located in the sex chromosome (especially an X chromosome).(2) Pertaining to a character or trait determined by gene(s) located in the sex chromosome(s).

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Hemizygous

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Pertaining to a diploid cell with only one copy of a gene instead of the usual two copies.

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Carrier

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A heterozygous individual bearing an unexpressed defective gene.(2) An organism possessing a recessive gene for a trait, hence, not expressing the trait.

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Sex Pilus

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Conjugation Tube

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The appendage that connects two bacterial cells together during conjugation.

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Plasmid

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A linear or circular double-stranded DNA that is capable of replicating independently of the chromosomal DNA.