Genetic Disorders &
Chromosomal
Mutations
Chapter 12
Karyotype
Karyotype: picture of homologous
chromosomes arranged in pairs
Human = 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
PKU
Tay
Sachs
Recessive Allele Disorders

3) Cystic Fibrosis: Causes respiratory and
digestive problems


Most common fatal genetic disorder
4) Sickle Cell Disease: Results in bent
and twisted red blood cells; ↓ blood O2
levels
Causes physical weakness; brain, heart, and
spleen damage; death
 Closely linked to malaria

Cystic Fibrosis
Sickle Cell Disease
Dominant Allele Disorders
Always revealed (even if recessive
allele is present)
 Disorders:

1) Acondroplasia: type of dwarfism
 2) Huntington’s disease: progressive
loss of muscle and mental functioning

• No symptoms until in 30’s
Mutations

Mutation: any change in DNA
May involve entire chromosome or
single nucleotide
 May take place in ANY cell
 May 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 nonhomologous chromosomes