Sex linked inheritance

Human Genome Autosomes (1 – 22) Sex Chromosomes (X and Y)

X Y

SEX-LINKED RECESSIVE TRAITS

Haemophilia X-linked recessive inheritance causes people to continue bleeding for a long time unless treated

Haemophilia

COLOUR BLINDNESS

Colour blindness: Alleles: X+ = normal vision, Xc = colour blind (X+ is dominant) phenotypes female genotypes male genotypes normal X+ X+ X+ Y colour blind Xc Xc Xc Y carrier* X+ Xc * carrier - transmits but does not express a trait

Carrier female Xc Xc X+Xc XcY X+ Y Female’s gametes Male’s gametes Colorblind male X+ Male’s gametes Y

Affected individuals female male carrier ? Unknown phenotype progeny

GENERATIONS Generations are numbered w/Roman numerals. Within each generation, individuals are numbered from oldest to youngest.

Baldness

Fragile X Syndrome Fragile X syndrome (or Marker X syndrome ) is a genetic condition involving changes in the long arm of the X chromosome. It is characterized by mental retardation.