+

Chromosome Number Mutations8.19 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

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