Genetics Exam 2
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52 terms
Terms | Definitions |
|---|---|
 Tay-Sachs Disease | most common in Ashkenazi Jews; caused by a mutation in the gene for the alpha subunit of hexosaminidase A; progressive neurodegenerative disorder; usually fatal by age 2-3 |
| incomplete dominance | parents with very different traits result in offspring having an intermediate phenotype (black and white parents have grey child) |
| codominance | simultaneous expression of two alleles (of the same gene) encoding two distinct products (e.g. the MN blood type) |
| phenotypic expression | the gene expression and the resulting phenotype are often modified thought the interaction between genotypes and the environment |
| penetrance | the percent of individuals showing at least some degree of expression of a mutant genotype; some percent of individuals known to exhibit disease symptoms do not |
| expressivity | refers to nature and severity of the phenotype produced by the mutant genotype; variable this is a frequent characteristic of autosomal dominant traits (e.g. Neurofibromatosis) |
| genetic suppression | the expression of other genes throughout the genome may affect the phenotype normally produced by the mutant gene in question |
| position effects | the physical location of the gene in relation to other sequences in the genome may influence its expression (e.g. translocation resulting in hyper-expressivity) |
| temperature | the reason that fur color in Himalayan rabbits is different in some areas than others |
| dominant alleles | the Ia and the Ib genes that determine blood type |
| recessive allele | the Io gene that determines blood type |
| recessive lethal allele | a homozygous recessive combination of alleles results in death and modified Mendelian ratios |
| dominant lethal allele | a homozygous dominant or heterozygous combination of alleles results in death (e.g. Huntington's disease) |
| new phenotypes | gene interactions can yield novel phenotypes in the F2 generation |
| epistasis | the interaction of nonallelic genes in the formation of the phenotype; the expression of one gene pair masks the expression of a second gene pair |
| autosomal | 93.8% of human genetic disorders are this category; linked to the non-sex chromosomes |
| X linked | 5.6% of human genetic disorders are this category; affects mostly men |
| Y linked | 0.29% of human genetic disorders are this category; affects only men |
| mitochondrial | 0.32% of human genetic disorders are this category; takes place in DNA not in the nucleus |
| familial hypercholesterolemia | an autosomal dominant disorder that is manifest in abnormally high levels of serum cholesterol |
| Erythromelalgia | an autosomal dominant disorder that is classified by red, hot, painful feet and hands; disease shows reduced penetrance (90%) |
| Marfan Syndrome | an example of variable expressivity; autosomal dominant; 1-3 organ systems may be affected (pleiotropic); a connective tissue disorder due to a mutation in the gene encoding fibrillin |
| Cystic fibrosis | autosomal recessive disease; characterized by sticky, viscous secretions from the lungs and pancreas |
| Duchenne muscular dystrophy | X-linked recessive disease; characterized by the onset of muscle weakness before the age of 10; death before the age of 20 |
| Vitamin D-resistant rickets | also known as hypophosphatemia; X-linked dominant; characterized by crippling because of extremely low levels of phosphate in the blood |
| sex chromosomes | chromosomes that vary (size, gene content) depending on the gender |
| autosomes | all of the chromosomes other than the sex chromosomes |
| X linked | genes located on the X chromosome |
| Y linked | genes located on the Y chromosome |
| hemizygous | refers to genes on X chromosome in males; X-linked cannot be hetero- or homozygous in males due to the presence of the Y chromosome |
| pseudodominant | when the single copy of a recessive X linked allele in males determines the phenotype (since it's the only allele present) |
| hemophilia | an X linked disease that results in blood failing to clot; used to prevalent in the royal family; mostly affects males |
| Fabry's disease | an X linked disease that is characterized by a deficiency of alpha galactosidase A, leading to heart and kidney defects and early death |
| G6PD deficiency | an X linked disease that is characterized by a severe anemic reaction following the ingestion of primaquines (nutrient found in fava beans and some antimalarial) |
| Hunter Syndrome | an X linked disease that is characterized by a lysosomal storage disease, accompanied by short stature, and mental retardation |
| Lesch-Nyhan Syndrome | an X linked disease that is characterized by a deficiency of HGPRT, leading to mental retardation and self-mutilation |
| Duchenne Muscular Dystrophy | an X linked disease that is characterized by a deficiency of dystrophin, leading to muscle degeneration |
| sex limited inheritance | the expression of a given phenotype is strictly limited to one sex |
| sex influenced inheritance | the degree of expression of a given phenotype depends upon the gender of the individual; not limited to one gender or the other; often modified by sex chromosomes |
| parental phenotype | a phenotype identical to one or the other parent |
| recombinant phenotype | a phenotype unlike either parent |
| linkage group | genes on the same chromosome showing evidence of linkage |
| complete linkage | when no recombination ever occurs between two linked genes; inherited as a unit |
| positive interference | fewer double crossovers observed than expected |
| negative interference | more double crossovers observed than expected |
| mitotic recombination | the explanation for the yellow and singed spots on fruit flies |
| somatic cell hybridization | a method of localizing human genes to a particular chromosome; accomplished by combining mouse and human cells |
| one to one | the ratio of parental ditypes to nonparental ditypes in unlinked genes |
| first division segregation | no crossing over in division of an ascus |
| second division segregation | crossing over between the gene and its centromere in the division of an ascus |
| Thomas Hunt Morgan | geneticist that first observed sex-linked coloring patterns in Drosophila |
| Creighton and McClintock | two scientists who studied Zea mays and observed cytological evidence for recombination |
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