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Patterns of Chromosome Inheritance Chapter 24 Karyotyping • Karyotype – Size-ordered chart of the metaphase chromosomes of an individual cell • Chromosomal aberration – A mutation that is large enough to see under a light microscope Amniocentesis Chorionic villi sampling Normal male karyotype Down syndrome karyotype Changes in Chromosome Number • Nondisjunction • Result after fertilization: – Trisomy – Monosomy Nondisjunction in Meiosis I Nondisjunction in Meiosis II Down Syndrome Changes in Sex Chromosome Number • Y chromosome-determines maleness. • SRY gene produces a testis-determining factor • Caused by non-disjunction Non-disjunction in Sex Chromosomes Y chromosome-determines maleness. Results of non-disjunction?: XXX Survivable with problems XXY Survivable with problems XYY Survivable with problems X0 Survivable with problems 0Y Lethal • • • • Non-disjunction in Sex Chromosomes Turner Syndrome --XO Klinefelter Syndrome—XXY Poly-X Females---XXX Jacobs Syndrome---XYY Changes in Chromosome Structure • Mutation– a permanent genetic change. • Chromosome mutation--change in chromosome structure. • Types: – Inversion – Translocation – Deletion – Duplication Deletion Duplication Translocation Inversion WHAT’S HAPPENING?? Sex-Linked Traits • Traits controlled by genes on the X or Y chromosomes are sex-linked although most are unrelated to gender. • An allele on the X chromosome that is in the region where the Y chromosome has no alleles will express even if recessive; it is termed X-linked. • A female would have to have two recessive genes to express the trait; a male would only need one. X-Linked Alleles • The key for an X-linked problem shows the allele attached to the X as in: • XB = normal vision • Xb = color blindness. • Females with the genotype XBXb are carriers because they appear to be normal but each son has a 50% chance of being color blind depending on which allele the son receives. • XbXb and XbY are both colorblind. Cross involving an X-linked allele X-linked recessive pedigree chart X-Linked Disorders • Red-green color blindness • Muscular dystrophy. • Hemophilia. http://perth.uwlax.edu/faculty/howard/BIO101/DNA&translation/sld002.htm Diana http://brie.medlabscience.med.ualberta.ca/de/genetics/70gen-hemophil.html Chapter Summary • Humans - 22 pairs of autosomes and one pair of sex chromosomes • Abnormalities of chromosome number or composition. • Males - XY • Females -XX. • Chromosomal mutations • Sex-linked traits