Human Growth and Development / Unit 2 HGD 0167 worked example, 60 to 90 seconds
Three Kinds of Genetic Disorder
The idea
Genetic disorders come in three kinds. A single-gene disorder follows from one gene: a pair of recessive alleles, as in cystic fibrosis or Tay-Sachs, or a mutation. A chromosomal disorder follows from a change in a whole chromosome's structure or number, as in Down syndrome, an extra copy of chromosome twenty-one. A multifactorial disorder follows from many genes interacting with the environment, as in type two diabetes and heart disease. Screening can take place before pregnancy, during it, or after birth.
In practice
Three routes to a diagnosis: one faulty gene, one whole chromosome altered, or many genes meeting a particular life.
Where people slip
The kind of disorder decides which test can find it, a point the prenatal testing entries return to. A chromosomal count shows up in a sample of fetal cells; a structural difference in a body part shows up on an image. Screening before pregnancy can show whether both parents carry the same recessive allele.
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