Chapter 4
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42 terms
Terms | Definitions |
|---|---|
 gene interaction | production of novel phenotypes by the interaction of products of alleles of different genes |
| x-linkage | the pattern of inheritance resulting from genes located on the X chromosome |
| wild-type allele | the most commonly observed phenotype or genotype designated as the norm or standard |
| loss-of-function mutation | mutations that produce alleles with reduced or no function |
| null allele | a mutant allele that produces no functional gene product. usually inherited as a recessive trait |
| gain-of-function mutations | a mutation that produces a phenotype different from that of the normal allele and from any loss of function alleles |
| neutral mutations | a mutation with no immediate adaptive significance or phenotypic effect |
| incomplete / partial dominance | expressing a heterozygous phenotype that is distinct from the phenotype of either homozygous parent. |
| Tay-Sachs disease | autosomal recessive, a lethal lipid metabolism disease involving an abnormal enzyme |
| codominance | condition in which the phenotypic effects of a gene's alleles are fully and simultaneously expressed in the heterozygote |
| multiple alleles | in a population of organisms, three or more alleles of the same gene |
| Bombay phenotype | a rare variant of hte ABO antigen system in which affected indiviuals do not have A or B antigens and thus appear to have blood type O, even though their genotype may carry unexpressed alleles for the A and/or B antigens |
| Huntington disease | due to a dominant autosomal allele H, where the onset of the disease in heterozygotes(Hh) is delayed, usually well into adulthood. Affected individuals then undergo gradual nervous and motor degeneration until they die. |
| complementation analysis | allows us to determine whether two such mutations are in the same gene or whether they represent mutations in separate genes |
| pleiotropy | condition in which a single mutation causes multiple phenotypic effects |
| Marfan syndrome | results from an autosomal dominant mutation in the gene encoding the connective tissue protein fibrillin |
| prophyria variegata | cannot adequately metabolize the prophyrin component of hemoglobin when hemoglobin is broken down as red blood cells are repalced |
| x-linkage | the pattern of inheritance resulting from genes located on the X chromosome |
| hemizygous | Having a gene present in a single does in an otherwise diploid cell. Usually applied to genes on the X chromosome in heterogametic males |
| crisscross pattern of inheritance | phenotypic traits controlled by recessive x-linked genes are passed from homozygous mothers to all sons |
| chromosome theory of inheritance | The idea put forward independently by Walter Sutton and Theodor Boveri that chromosomes are the carriers of genes and the basis for the Mendelian mechanisms of segregation and independent assortment |
| sex-limited inheritance / sex-influence inheritance | phenotypic expression that is conditioned by the sex of the individual. A heterozygote may express one phenotype in one sex and alternate phenotype in the other sex (e.g., pattern baldness in humans) |
| penetrance | the frequency, expressed as a percentage, with which individuals of a given genotype manifest at least some degree of a specific mutant phenotype associated with a trait |
| expressivity | the degree or range in which a phenotype for a given trait is expressed |
| genetic background | the collective genome of an organism, as it impacts on the expression of a gene under investigation |
| position effect | change in expression of a gene associated with a change in the gene's location within the genome |
| heterochromatin | the heavily staining, late-replicated regions of chromosomes that are prematurely condensed in interphase. |
| temperature-sensitive mutations | a conditional mutation that produces a mutant phenotype at one temperature range and a wild-type phenotype at another |
| conditional mutations | a mutation that is expressed only under a certain condition; that is a wild-type phenotype is expressed under certain (permissive) conditions and a mutant phenotype under other (restrictive conditions) |
| Lesch-Nyhan syndrom | inherited as an X-linked recessive disease; characterized by abnormal nucleic acid metabolism |
| Duchenne muscular dystrophy (DMD) | an x-linked recessive genetic disorder caused by a mutation in the gene for dystrophin, a protein found in muscle cells. Affected males show a progressive weakness and wasting of muscle tissue. Death ensues about age 20 caused by respiratory infection or cardiac failure |
| genetic anticipation | the phenomenon in which the severity of symptoms in genetic disorders increases and the age of onset decreases from generation to generation. It is caused by the expansion of trinucleotide repeats within or near a gene and was first observed in myotonic dystrophy |
| Myotonic dystrophy (DM) | autosomal dominant disorder; exhibit extreme variation in the severity of symptoms |
| genomic / parental imprinting | the process by which the expression of a gene depends on whether it has been inherited from a male or a female parent |
| Prader-Willi syndrome (PWS) | results only when an undeleted maternal chromosome remains |
| Angelman syndrome (AS) | results only if an undeleted paternal chromosome remains |
| maternal effect | phenotypic effects in offspring attributable to genetic information transmitted through the oocyte derived from the maternal genome |
| extranuclear inheritance | transmission of traits by genetic information contained in cytoplasmic organelles such as mitochondria and chloroplasts |
| myoclonic epilepsy and raggedred fiber disease (MERRF) | inherited (maternal transmission) express ataxia, deafness, dementia, and epileptic seizures |
| Leber's hereditary optic neuropathy (LHON) | maternal inheritance and has mitochondrial DNA lesions |
| epigensis | the idea that an organism or organ arises through the sequential appearance and development of new structures |
| epistasis | nonreciprocal interaction between nonallelic gene such that one gene influences or interferes with the expression another gene, leading to a specific phenotype |
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