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chromosome theory of inheritance Mendelian genes have a specific loci on chromosomes and it's the chromosomes that undergo segregation and independent assortment TH Morgan came up with the first solid evidence associating a specific gene with a specific chromosome wild type normal phenotype for a character mutant traits alternative to the wild type linked genes genes located on the same chromosome that are usually inherited together in genetic crosses don't assort independently genetic recombination production of offspring with combinations of traits differing from those found in either parent parental types offspring matching one of the parents recombinant types offspring with new combinations of traits don't exactly look like parents crossing over Morgan's conclusion "genes can be linked but the linkage is incomplete" sooooooo...some process must sometimes break the physical connection between genes on the same chromosome. What is the name of that process? genetic/linkage map based on recombination frequencies map units one= 1% recombination frequency SRY gene codes for protein that regulates other genes that lead to development of testes on Y chromosome XY system humans fruit flies XO grasshoppers crickets roaches insects ZW birds fish butterflies moths sex linked gene gene located on either sex chromosome Duchenne muscular dystrophy sex linked disease (X chromosome) progressive weakening of the muscles and loss of coordination afflicted rarely live past 20's result of an absence of a key muscle protein (dystrophin) hemophilia sex linked disease (recessive) absence of one or more proteins required for blood clotting can be treated with injections of the missing protein Barr body inactive X in each cell of a female condenses into a compact object lies along nuclear envelope nondisjunction occasional mishap in which the members of a homologous chromosomes don't move apart properly during meiosis I or sister chromatids fail to separate during meiosis II one gamete receives two of the same type of chromosome and another gametes gets no copy aneuploidy if either of the aberrant gametes unite with a normal gamete at fertilization the offspring will have an abnormal number of a particular chromosome trisomy zygote has 3 copies of a particular chromosome 2n+1 monosomy zygote has only one copy of a particular chromosome 2n-1 polyploidy condition where organism has more than 2 complete sets of chromosomes common in plants syndrome sypmtoms of surviving individuals diagnosed with karyotype Down Syndrome trisomy 21 affects 1/700 kids in US frequency increases with the age of the mother Klinefelter Syndrome resulted from a nondisjunction of sex chromosomes producing a variety of aneuploid conditions XXY (male)- girlesque Turner Syndrome resulted from a nondisjunction of sex chromosomes producing a variety of aneuploid conditions monosomy X (female)- sterile, only viable human monosomy Metafemale XXX (trisomy X) limited fertility deletion removal of a chromosome segment duplication repeats a segment inversion reverses a segment within a chromosome translocation moves a segment from one chromosome to another Cri du Chat "Cry of the Cat" caused by a deletion of chromosome 5 symptoms: mentally retarded, small head, unusual facial features die in infancy Chronic Myelogenous Leukemia CML caused by a reciprocal translocation between chr. 22 and chr. 9 symptoms: cancer cells give rise to white blood cells which lower immune system Philadelphia chromosome small chr. 22 Prader-Willi Syndrome caused by a deletion of chr. 15 from father symptoms: mental retardation, obesity, short Angelman Syndrome (AS) caused by a deletion of chr. 15 from mother neurogenetic disorder symptoms: intellectual and developmental delay, sleep disturbance, seizures, jerky movements, unusually happy demeanor genomic imprinting phenotype depends on which parent passed along the alleles for the trait includes silencing of one allele of certain genes extranuclear genes found in organelles in cytoplasm traits depend on maternal parent because the zygote's cytoplasm comes from an egg 50% Chance of recombination when genes are on different chromosomes.