Vocabulary

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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

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A

• Aneuploidy - Having particular chromosomes or regions of chromosomes in extra or fewer copies than in the wild type.
• Allele - One of the different forms of a gene that can exist at a single locus.
• Autosomes - Chromosomes that are not sex chromosomes.
• Amporh - Amorphic describes a mutation that causes complete loss of gene function.[1] Amorph is sometimes used interchangeably with "genetic null". An amorphic mutation might cause complete loss of protein function by disrupting translation ("protein null") and/or preventing transcription ("RNA null"). An amorphic allele elicits the same phenotype when homozygous and when heterozygous to a chromosomal deletion or deficiency that disrupts the same gene. This relationship can be represented as follows: m/m = m/Df. An amorphic allele is commonly recessive to its wildtype counterpart. It is possible for an amorph to be dominant if the gene in question is required in two copies to elicit a normal phenotype (i.e. haploinsufficient).
• Antimorph - are dominant mutations that act in opposition to normal gene activity. Antimorphs are also called dominant negative mutations. Increasing wildtype gene function reduces the phenotypic severity of an antimorph, so the phenotype of an antimorph is worse when heterozygous than when in trans to a gene duplication. m/+ > m/Dp. An antimorphic mutation might affect the function of a protein that acts as a dimer so that a dimer consisting of one normal and one mutated protein is no longer functional.

B

• Back Mutation - The process that causes reversion. A change in a nucleotide pair in a mutant gene that restores the original sequence and hence the original phenotype.
• Balancer Chromosome - Balancer chromosomes are special, modified chromosomes used for genetically screening a population of organisms to select for heterozygotes. They have three functional characteristics:
  • They have many inversions to eliminate recombination from occurring.
  • They confers an easily scored dominant phenotype.
  • They are recessive lethal.
• Bypass suppressor - suppress all mutant alleles of a gene, including null alleles, and hence bypass the requirement for a gene. These suppressors are gene specific, allele nonspecific. There are three types of bypass suppressors that we will consider here.

C

• Cell autonomy - A genetic trait in multicellular organisms in which only genotypically mutant cells exhibit the mutant phenotype. Conversely, a nonautonomous trait is one in which genotypically mutant cells cause other cells (regardless of their genotype) to exhibit a mutant phenotype.
• Centimorgan - distance between chromosome positions (also termed, loci or markers) for which the expected average number of intervening chromosomal crossovers in a single generation is 0.01.
• Codominance - When a heterozygote shows the phenotypic effects of both alleles equally.
• Complementation - occurs when two strains of an organism with different homozygous recessive mutations that produce the same mutant phenotype produce offspring with the wild-type phenotype when mated or crossed.
• Cytokinesis - the process in which the cytoplasm of a single eukaryotic cell is divided to form two daughter cells.

D

• Diploid - An individual with two sets of homologous chromosomes.
• Dihybrid Cross - a ross between two individuals identically heterozygous at two loci.
• Dominant - The phenotypic trait observed in an individual heterozygous a particular locus.
• Dominant Negative - (antimorph) - a mutation that acts antagonistically to the wild-type allele. Therefore, the presence of a dominant negative allele will alter the phenotype even in the presence of the wild type allele.

E

• EMS - Ethyl methanesulfonate (EMS) is a mutagen. It produces random mutations in genetic material by nucleotide substitution; particularly by guanine alkylation. This typically produces only point mutations.
• Enhancer - enhancers modify the existing mutant phenotypes by making the mutant phenotype worse (enhancing it). The normal function of the enhancer gene acts with the same effect as the original gene.
• ENV - also known as N-ethyl-N-nitrosourea (chemical formula C3H7N3O2), is a highly potent mutagen. For a given gene in mice, ENU can induce 1 new mutation in every 700 loci. It is also toxic at high doses.
• Expressivity - the level of variation observed in a mutant phenotype among individuals carrying the same genotype.
• Epistasis - A situation in which the differential phenotypic expression of a genotype at one locus depends on the genotype at another locus; a mutation that exerts its expression while cancelling the expression of the alleles of another gene.
• Extragenic Suppressor - results from suppressor mutations that occur in a different gene as the original mutation.

F

• F2 non-clonal screen - When screening F2 progeny that arose from multiple Po individuals
• F2 recessive screen - Mutagenize Po, Self F1 progeny, and search for mutant phenotypes in F2

G

• Gain-of-function mutation A type of mutation in which the altered gene product possesses a new molecular function or a new pattern of gene expression. Gain-of-function mutations are almost always Dominant or Semidominant.
• Gene - the unit of heredity.
• Gene-dosage effect - A change in phenotype caused by an abnormal number of wild-type alleles.
• Genetic Selection - A growth condition that allows for selective propagation of genetically marked cells.
• Genetic Screen - A growth condition where both mutant and wild-type are able to grow but can be distinguished phenotypically.
• Genotype - All of the alleles of an individual. The allelic composition at one gene.

H

• Haploid - An individual with one set of chromosomes.
• Haploinsufficient - Occurs in diploid organisms when a single functional copy of a gene does not produce enough of a gene product (typically a protein) to bring about a wild-type condition.
• Haplotype - A combination of alleles, often tightly linked and inherited through generations.
• Hemizygous gene - Gene present in only one copy in diploid individual.
• Heterozygous - A diploid individual with two different alleles of a gene.
• Homozygous - A diploid individual with two of the same alleles of a gene.
• Hybrid Cross - Cross between two F1 offspring generated by breeding two true breeding lines.
• Hypermorph - A hypermorphic mutation causes an increase in normal gene function. Hypermorphic alleles are gain of function alleles. A hypermorph can result from an increase in gene dose (a gene duplication), from increased mRNA or protein expression, or constitutive protein activity. The phenotype of a hypermorph is worsened by increasing the wildtype gene dose, and is reduced by lowering wildtype gene dose. m/Dp > m/+ > m/Df
• Hypomorph - describes a mutation that causes a partial loss of gene function. A hypomorph is a reduction in gene function through reduced (protein, RNA) expression or reduced functional performance, but not a complete loss. The phenotype of a hypomorph is more severe in trans to a deletion allele than when homozygous. m/DF > m/m. Hypomorphs are usually recessive, but occasional alleles are dominant due to haploinsufficiency.

I

• Incomplete Dominance - When a heterozygote shows a phenotype quantitatively (but not exactly) intermediate between the corresponding homozygote phenotypes.
• Incomplete Penetrance - the proportion of individuals carrying a particular variant of a gene that also expresses an associated trait.
• Intragenic complementation - During intragenic complementation, alleles of the same gene complement one another, even though both alleles produce a faulty gene product. There are different means by which mutant alleles of the same gene can mutually correct one another. First, one mutant gene product may reduce the dosage of the other mutant product. Second, a faulty complex formed by one mutant gene product may be stabilized by the presence of an alternatively mutant gene product. Third, a gene product containing a mutation that affects one function may provide the function missing from an alternatively altered gene product.
• Intragenic non-complementation - Mutations in the same gene that fail to complement each other.
• Intragenic Suppressor - results from suppressor mutations that occur in the same gene as the original mutation.
• Inversion - A chromosomal mutation consisting of the removal of a chromosome segment, its rotation through 180º, and its reinsertion in the same location.

J

K

• Karyotype - The number and appearance of chromosomes in a eukaryotic nucleus.

L

• Locus - Site on a chromosome where a gene is located.
• Loss-of-function mutation - also called inactivating mutations, result in the gene product having less or no function (being partially or wholly inactivated). When the allele has a complete loss of function (null allele), it is often called an amorphic mutation in the Muller's morphs schema.

M

• Marey Map - A visual representation of the relationship between genetic linkage and physical location of genetic markers.
• Meiosis - Two successive nuclear divisions (with corresponding cellular division) that produce gametes (in animals) or sexual spores (in plants and fungi) that have one-half of the genetic material of the original cell.
• Mitosis - TA type of nuclear division (occurring at cell division) that produces two daughter nuclei identical with the parent nucleus.
• Mitotic Recombination - Mitotic recombination is a type of genetic recombination that may occur in somatic cells during their preparation for mitosis in both sexual and asexual organisms.

N

• Nondisjunction - The failure of homologs (meiosis) or sister chromatids (mitosis) to separate properly to opposite poles.
• Neomorph - A neomorphic mutation causes a dominant gain of gene function that is different from the normal function. A neomorphic mutation can cause ectopic mRNA or protein expression, or new protein functions from altered protein structure. Changing wildtype gene dose has no effect on the phenotype of a neomorph. m/Df = m/+ = m/Dp

O

P

• Penetrance - the extent to which a particular gene or set of genes is expressed in the phenotypes of individuals carrying it, measured by the proportion of carriers showing the characteristic phenotype.
• Phenotype - The form taken by some character (or group of characters) in a specific individual. The detectable outward manifestations of a specific genotype.
• Phenotypic Ratio - proportion of cross progeny with specific phenotypes.
• Pleiotropy - Occurs when one gene influences multiple, seemingly unrelated phenotypic traits
• Poisson Distribution - A mathematical distribution giving the probability of observing various numbers of a particular event in a sample when the mean probability of an event on any one trial is very small.
• Polyploidy - Containing more than two homologous sets of chromosomes.
• Polytene Chromosome - A giant chromosome in specific tissues of some insects, produced by an endomitotic process in which multiple DNA sets remain bound in a haploid number of chromosomes.

Q

R

• Recessive - The phenotypic trait not observed in an individual heterozygous a particular locus.
• Recipricol Cross - a pair of crosses between a male of one strain and a female of another, and vice versa.
• Revertant -An allele with wild-type function arising by the mutation of a mutant allele; caused by a complete reversal of the original event or a compensatory second event.

S

• Screen - A mutagenesis procedure in which essentially all mutagenized progeny are recovered and are individually evaluated for mutant phenotype.
• Selection - An experimental procedure in which only a specific type of mutant can survive.
• Self cross - Crossing an individual to itself.
• Suppressor - Suppressors make a mutant phenotype better. Their normal function acts oppositely to the function of the originally mutated gene.
• Synthetic Lethality - Lethality resulting from a combination of mutations occurring in two or more genes.

T

• Test Cross - Cross of an individual with an individual that is homozygous for alleles that confer the recessive phenotype.
• Trans - When two genes or mutations are in trans they are located on homologous chromosomes.
• True-breeding strain - line of individuals that when crossed with itself will always produce offspring with the same phenotype.
• Twin spots - two neighboring groups of cells in drosophila that are a result of mitotic recombination that segregates a heterozygous cell into two reciprocal homozygous cells expressing different markers

U

V

W

X

Y

Z