+ Chromosome Number Mutations 8.19 to 8.23

+ Karyotype Photographic display of metaphase chromosomes arranged by size and centromere position Used to identify chromosome number disorders Chromosome pairs 1 to 22 Autosomes Chromosome pair 23 Sex Chromosomes What sex is shown here? female

+ Down Sydnrome Trisomy 21 3 copies of chromosome 21 Symptoms Heart and respiratory defects Short in stature Flattened nose bridge Skin fold in the corner of eye Single skin fold in palm Small ears, hands, and feet Varying degrees of mental retardation

+ Nondisjunction Mutation / accident during cell division Homologous chromosomes fail to separate in meiosis I Sister chromatids fail to separate in meiosis II or mitosis Results in extra or missing chromosomes Which has a greater impact mieotic nondisjuction or mitotic nondisjuntion? Why? Mieiotic – passed to future generations

+ Sex Chromosomes Why is nondisjunction of sex chromosomes usually not fatal? Y – contains few genes, genes that are nonvital, genes that code for male characteristics X – mammals function with only one X activated per cells; if one is missing there is still one present to code for vital life functions NOTE: one X must be present, without an X, life ceases

+ Chromosomal Mutations Deletion -Loss of part of DNA sequence; eliminate a gene or alter gene products Duplication – repetition of part of a chromosome Inversion – change in gene order on chromosome Translocation – exchange of genetic material between nonhomologous chromosomes