Genetics study guide

The Human Genome Project (HGP), an international scientific research project, successfully determined the sequence of the human genome, mapping out all the genes within human DNA. This monumental undertaking involved identifying the approximately 20,000 to 25,000 genes in human DNA and mapping their locations on chromosomes. The HGP provided a comprehensive reference sequence of the human genome, a foundational achievement that opened new avenues for understanding human biology, health, and disease. Its findings have significantly impacted medical science, leading to advancements in disease diagnosis, targeted therapies, and personalized medicine, where treatments can be tailored to an individual's genetic profile.

X-linked recessive genetic disorders are caused by faulty alleles located on the X chromosome. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). Since males have only one X chromosome, a single copy of the recessive faulty allele on their X chromosome is enough for them to express the disorder. In contrast, females must inherit the faulty allele on both of their X chromosomes to be affected. If a female inherits only one faulty allele, she is a carrier: she will not usually show symptoms but can pass on the faulty allele to her children. These disorders, such as red-green colour blindness and haemophilia, are therefore more common in males. Fathers with X-linked recessive disorders pass the X chromosome to all of their daughters, making them carriers if the mother provides a normal allele.