Skip to 0 minutes and 11 secondsChromosomes 1 to 22 are the autosomes, and the 23rd pair are the sex chromosomes. We have two copies of all autosomal genes. In an autosomal dominant condition, the mutation in one copy of the genes leads to disease. With each conception a parent passes on one gene from the pair. Which one they pass on is due to chance. In automosal dominant inheritance there is a 50% or 1-in-2 chance of an affected parent passing on the condition to their children. This is because there are four possible combinations of genes that the children of that couple can inherit. Two out of four of these combinations result in a child inheriting the abnormal gene and being affected with the condition.
Skip to 0 minutes and 50 secondsTwo out of the four result in the child inheriting the normal copy of the gene and being unaffected. Features that may lead you to suspect an autosomal dominant inheritance pattern include both male and females being affected in roughly equal proportions, people in more than one generation being affected, and men and women both being able to pass on the condition to their sons and daughters. An example of an autosomal dominant condition is hereditary breast and ovarian cancer predisposition. This is known in the press a lot recently following Angelina Jolie's decision to undergo prophylactic bilateral mastectomies and subsequent bilateral oophorectomies. Jolie, who has a pathogenic mutation in BRCA1, lost her mother, aunt, and grandmother to cancer.
Skip to 1 minute and 33 secondsHere we can see that the pedigree has affected people in three generations.
Autosomal dominant inheritance
In this video, we learnt about autosomal dominant inheritance, where an affected individual has a mutation in one gene of a pair.
The main features of autosomal dominant inheritance pattern include:
- Males and females are affected in roughly equal proportions.
- People in more than one generation are affected.
- Men and women are both able to pass on the condition to their sons and daughters.
Angelina Jolie’s family tree in pedigree form Click to expand
© St George’s, University of London
The image above depicts a simplified version of Angelina Jolie’s family pedigree, illustrating how an autosomal dominant condition can be passed down through 3 generations.
The actress, who has a pathogenic mutation in BRCA1, lost a number of her immediate family to cancer: her mother, her aunt, and her grandmother.
We can see that the emergence of a greater understanding of genomics has already led to some difficult choices. What are, if any, your views on this?
Image: ©“Angelina Jolie - World Economic Forum Annual Meeting Davos 2005” by Remy Steinegger / World Economic Forum. Licensed by CC BY-NC-SA 2.0
© St George’s, University of London and Health Education England