Pedigree, twins, karyotype and chromosomal disease

Pedigree is social-looking ink for a genetic argument. Genealogical method maps kin roles; pedigree maps alleles.

• Pedigree: inheritance drawn across generations — squares/circles, shading, generations.
• Autosomal recessive: skips generations; affected often from carrier × carrier (sickle-cell, thalassaemia, Tay–Sachs, cystic fibrosis).
• Autosomal dominant: usually every generation; one affected parent.
• X-linked recessive: more males; no father-to-son; carrier mothers.
• X-linked dominant: both sexes; males often more severely affected.

• Monozygotic: one zygote splits; ~100% shared genes; same sex.
• Dizygotic: two eggs; ~50% like ordinary siblings; sex may differ.
• Concordance gaps between MZ and DZ estimate heritability — always add environment.
• Australian twin smoking/bone-density (Hopper & Seeman): smoking twin vs non-smoking co-twin isolates behaviour from genome.
• Foster / adoption designs (Minnesota-type teaching cases; home-quality and IQ): genes travel with the child, homes still move scores.
• Nature–nurture pegs: Locke’s blank slate, Mead on culture and personality, Kardiner–Linton, Bandura’s Bobo doll — environment teaches; it does not write a new DNA sequence.

• Karyotype: chromosomes photographed, paired, ordered by size — aneuploidy and big rearrangements show up.
• Humans and chimpanzees: ancestor with 24 pairs; two fused into human chromosome 2 — a phylogenetic teaching fact.
• Banding and FISH locate finer lesions. NIPT, amniocentesis, CVS are prenatal routes — ethics belong in the same paragraph.

• Deletion, duplication, inversion, translocation.
• Robertsonian fusion of acrocentrics (14 and 21) → familial Down syndrome risk.
• Gene-dosage mess hits many organs at once — that is why chromosomal disease is ‘syndromic’.