Biological Factors Affecting Growth and Development.

Genetic Inheritance.
1. 23 pairs of chromosomes.
  1. Made of DNA which carries inheritence known as genes.
    1. DNA = Deoxyribonucleic acid
  2. Fathers donation of the Y chromosome in the 23rd pair which determines the sex of the child.
Chromosome Abnormalities.
1. 1 in 200 babies born alive has chromosome abnormalities.
2. Down's Syndrome - Trisomy 21.
  1. 1 in 650 babies are born with Trisomy 21.
  2. Trisomy 21 = Presence of 3 chromosomes at pair 21
  3. More present in women in their late 30's and 40's
    1. Offered invaisive tests of sampling foetal cells from the amniocentesis or chronic villus sampling.
  4. Small facial features with eyes that slope upwards at the outer corners.
    1. Skin folds covering the nasal corners.
      1. Tongue is large and protruding.
    2. Hands are short and broad with unusual palm creases.
      1. Back of head is flat.
  5. Less than a generation ago, many Down's Syndrome children did not live past adolescence.
Unifactorial Disorders.
1. Cause considerable disability.
2. Divided into Autosomal Disorders and Sex-linked Disorders.
  1. Autosomal Disorders.
    1. 23 pairs of chromosomes.
      1. Composed of 2 units called alleles, each of which is on a single chromosome.
        Each allele originate from parent.
        2 alternative forms.
        The gene could be composed of 2 alleles, BB bb or Bb.
  2. Sex-linked Disorders.

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