Biological Factors Affecting Growth and Development.

Biological Factors Affecting Growth and Development.

1. Genetic Inheritance.

   • 23 pairs of chromosomes.
     • Made of DNA which carries inheritence known as genes.
       • DNA = Deoxyribonucleic acid
     • Fathers donation of the Y chromosome in the 23rd pair which determines the sex of the child.

2. Chromosome Abnormalities.

   • 1 in 200 babies born alive has chromosome abnormalities.
   • Down's Syndrome - Trisomy 21.
     • 1 in 650 babies are born with Trisomy 21.
     • Trisomy 21 = Presence of 3 chromosomes at pair 21
     • More present in women in their late 30's and 40's
       • Offered invaisive tests of sampling foetal cells from the amniocentesis or chronic villus sampling.
     • Small facial features with eyes that slope upwards at the outer corners.
       • Skin folds covering the nasal corners.
         • Tongue is large and protruding.
       • Hands are short and broad with unusual palm creases.
         • Back of head is flat.
     • Less than a generation ago, many Down's Syndrome children did not live past adolescence.

3. Unifactorial Disorders.

   • Cause considerable disability.
   • Divided into Autosomal Disorders and Sex-linked Disorders.
     • Autosomal Disorders.
       • 23 pairs of chromosomes.
         • 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.
     • Sex-linked Disorders.