SEX-LINKAGE

• WHAT ARE AUTOSOMES?

  chromosome pairs 1-22, form homologous pairs
• WHAT ARE SEX CHROMOSOMES?

  chromosome 23, do not form homologous pairs
• WHAT IS A SEX-LINKED DISEASE?

  haemophilia
• WHY DOES SEX-LINKAGE OCCUR?

  • on most of length of X chromosome
  • there is no equivalent homologous portion on Y chromosome
  • characteristics caused by recessive alleles
  • on non-homologous portions of X
  • appear more frequently in males
• WHAT IS HAEMOPHILIA?

  • altered sequence of DNA nucleotide bases
  • code for a faulty protein
  • functional protein cannot clot