Post on 20-Jan-2016
Genetic Disorders & Chromosomal Mutations
Chapter 12
Karyotype
Karyotype: picture of homologous chromosomes arranged in pairsHuman = 46 chromos. = 23 pairs
Sex chromosomes = determine sex of human (1 pair)
• Male: XY • Female: XX
Autosomes = all others (22 pairs)
Pedigree Chart Shows relationships within a family
Each row is a different generation Males: ■ Females: ● Vertical: children; Horizontal: couples Solid shape: has trait
Used to track appearance of traits Can infer genotype of family members
Recessive Allele Disorders
Revealed only when dominant allele is absent
Disorders:1) PKU (phenylketonuria): newborns lack
enzyme to break down phenylaline in milk → severe mental retardation
2) Tay-Sachs: nervous system breakdown → death by age 4
• Mostly central and eastern Europeans
PKUTay Sachs
Recessive Allele Disorders
3) Cystic Fibrosis: Causes respiratory and digestive problemsMost common fatal genetic disorder
4) Sickle Cell Disease: Results in bent and twisted red blood cells; ↓ blood O2 levelsCauses physical weakness; brain, heart, and
spleen damage; deathClosely linked to malaria
Cystic Fibrosis Sickle Cell Disease
Dominant Allele Disorders
Always revealed (even if recessive allele is present)
Disorders:1) Acondroplasia: type of dwarfism2) Huntington’s disease: progressive
loss of muscle and mental functioning• No symptoms until in 30’s
Acondro
plasi
a
Huntington’sDisease
Mutations
Mutation: any change in DNAMay involve entire chromosome or
single nucleotideMay take place in ANY cellMay be beneficial or deadly (“lethal”)Occur in 2 types of cells:
• Germ-Cell Mutation: occur in gametes (sex cells); passed on to children
• Somatic Mutation: occur in body cells
Chromosome Mutations
Non-Disjunction: failure of chromosomes to separate during meiosis Results in gain/loss of
entire chromosome Trisomy 21: inheritance
of extra chromos. #21• “Down Syndrome”
Karyotype of Trisomy 21
Chromosome Mutations 1) Deletion: loss of piece of chromosome
Chromosome Mutations 3) Translocation: swapping segments of non-
homologous chromosomes