#
Unit 4 > Risks to health and well-being > Genetically inherited diseases and conditions

Genetically inherited diseases and conditions(cystic fibrosis, Down’s syndrome, heart condition)

Introduction

Each cell in the body contains 23 pairs of chromosomes.  One chromosome from each pair is inherited from an individual’s mother and one from their father.  The chromosomes contain genes that are inherited from an individual’s parents.  There are many different forms of the same gene e.g. eye colour.  These different forms are caused through mutations of the DNA code.  Some medical conditions are caused by a faulty version of a gene, where a normal version may not cause health problems.  Whether a child ends up with a medical condition will depend on:

  • The genes they inherit
  • Whether the gene for the condition is recessive or dominant

Gene mutations

Gene mutations occur when DNA is changes.  The  alterations in the genetic instructions may result in a genetic disorder or a change in characteristics.  Mutations are not spontaneous, DNA s constantly damaged by normal processes and natural chemicals e.g. water, oxygen, radiation and sunlight.   The damage is usually repaired, sometimes the repair is not perfect.  This can result in a mistake when the DNA is copied whilst the cell divides and cause a mutation.                   For example:       Cigarette smoke contains harmful chemicals that attack and damage DNA.  This can lead to a mutation in lung cell genes and cells that control growth. Over time this  leads to lung cancer.

The different effects of Mutations:

  • No effect, neutral
  • May be an improvement
  • May cause a disease

Genetic diseases

The most likely source of a genetic disease is inheritance from the parents.  More rarely a person have a genetic disease because a new mutation has occurred in their DNA.  Someone with a new mutation will not have a family history of a condition, but still be able to pass on the mutation to their offspring.