Chapter 15 - The Chromosomal Basis of Inheritance
Terms
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- Chromosome theory of inheritance
- according to this theory, Mendelian genes have specific loci on chromosomes and it is the chromosomes that undergo segregation and independent assortment
- Sex-linked genes
- genes located on a sex chromosome
- Linked genes
- genes located on the same chromosome that tend to be inherited together in genetic crosses because the chromosome is passed on as a unit
- Genetic recombination
- the general term for the production of offspring with new combinations of traits inherited from two parents
- Parental types
- offspring of a testcross that inherit a phenotype that matches one of the parental phenotypes
- Recombinants
- offspring of a testcross that inherit a completely different phenotype than either parent
- Genetic map
- an ordered list of the genetic loci along a particular chromosome; first devised by Alfred Sturtevant
- Linkage map
- a genetic map based on recombination frequencies; portrays the sequence of genes along a chromosome, but it does not give the precise location of genes
- Cytological maps
- a genetic map that locates genes with respect to chromosomal features, such as stained bands, that can be seen in the microscope
- Barr body
- in female mammals, often one of the two X chromosomes becomes inactivated and condenses into this compact object, which lies along the inside of the nuclear envelope; occurs during embryonic development
- Nondisjunction
- a meiotic mishap in which the members of a pair of homologous chromosomes do not move apart properly during meiosis I, or in which sister chromatids fail to separate during meiosis II; results in one gamete receiving two copies of the chromosome and one gamete receiving none; can also occur during mitosis
- Aneuploidy
- an abnormal chromosome number
- Trisomic
- an aneuploid cell with a 2n+1 chromosome count
- Monosomic
- an aneuploid cell with a n chromosome count
- Polyploidy
- a mutant characteristic of some organisms in which they have more than two complete chromosome sets
- Deletion
- occurs when a chromosomal fragment lacking a centromere is lost during cell division; results in a chromosome that is missing certain genes; especially likely to occur during meiosis
- Duplication
- a fragment of a chromosome breaks off and joins another section, thereby forming a duplicate section on the new chromosome; especially likely to occur during meiosis
- Inversion
- occurs when a chromosomal fragment breaks off and reattaches to the original chromosome in the reverse orientation
- Translocation
- occurs when a chromosomal fragment breaks off and joins to a nonhomologous chromosome
- Genetic imprinting
- known to occur in mammals, a process by which certain genes are imprinted in some way in each generation, with the imprinting status of a given gene depending on whether the gene resides in a female or in a male