Sex Linkage

• What is a sex linkage??

  the expression of an allele dependent on the gender of the individual as the gene is located on a sex chromosome
• how many pairs of autosomal chromosomes do humans have

  22
• autosomal chromosomes 


  • not involved in sex determination
• how many pairs of sex chromosomes do humans have

  1

  • Called either X or Y
• who has XY


  males

  • have one pf each type of sex chromosome
• Who has XX


  females

  • have 2 X chromosomes
• Where are most sex linked traits located

  on the X chromosomes with there being no equivalent locus on the Y chromosome

  • Therefore females will carry two alleles of sex linked gene, but males will only carry a single allele
• where is the genetic information for biological sex carried?

  on 2 sex chromosomes
• When is a characteristic said to be sex-linked?

  when the allele that codes for it is located on a sex chromosome
• Most genes on the sex chromosomes are only carried where?

  on the x chromosome (called X-linked genes)
• examples of X-Linked disorders

  colour blindness and haemophilia

  • caused by faulty alleles on the x-chromosome
• why do males often only have one allele for sex-linked genes?

  • Because they have only ONE X chromosome
  • only have one copy = males express the characteristic of this allele even if it is recessive
  • = makes males more likely than females to show recessive phenotypes for genes that are sex-linked