7.2 Autosomal Recessive Inheritance

Source 1: NIH || Autosomal Recessive Disorder

Definition

  • a pattern of inheritance characteristic of some genetic disorders

  • “autosomal” means the gene is located on one of the numbered, or non-sex, chromosomes

  • “Recessive” means two copies of the mutated gene is required to cause the disorder

  • both parents need to have the disease-causing alleles, rather than one gene like dominant inheritance

Narration

  • only occurs when both copies are mutated/not working

  • 2 nonworking genes come from both mom and dad

  • examples: sickle cell disease, cystic fibrosis, etc.

Source: VHS || Autosomal Recessive Inheritance

Chromosomes, Genes, and DNA

  • chromosome are long strings of genes in our bodies

  • genes message cells to make chemical products like proteins

  • “benign variants” or polymorphisms are variations that have no impact on our health

  • “pathogenic variant” or mutation are a variation of genes that cause health or developmental issues/conditions

  • when a condition only occurs when there are 2 copies of the changed gene they are recessive

    • if only 1 copy of genes causes the condition it is dominant

  • the autosomal gene is located on the numbered chromosomes and usually influence males and females the same way

    • X-linked genes are located on the X chromosome and impact males and females differently

A Close Look at Autosomal Recessive Inheritance

  • this type of inheritance refers to the inheritance of a recessive variant on an autosome

  • both copies of the gene send a message to the cells to produce particular products like protein

  • people who have a variant on 1 gene copy are called genetic carriers for a condition

    • genetic carriers do not show any symptoms of the recessive condition or develop related health problems

  • the cell can still work with only 1 gene copy making the right instructions   

  • if a person has both gene copies containing the variant, they do not have the ability to make enough gene product in the right way

    • will have symptoms of the genetic condition

YOU WILL ONLY HAVE SYMPTOMS IF THERE ARE 2 COPIES OF THE PATHOGENIC VARIANT

How are Autosomal Recessive Gene Variants Passed?

  • one copy of each gene is passed to a child from their mother and father

  • if both parents are carriers they have the chance to pass either a working or non-working gene to their baby

    • 25% chance of passing both working genes

    • 50% chance of passing both working and nonworking genes

    • 25% chance of passing both nonworking/affected genes

  • if one parent is a carrier there is no chance that the couple will have an affected baby   

    • 50% chance they will have carriers

    • 50% chance they will not have carriers

  • if one parent has the recessive condition and they marry a non-carrier, there is a 100% chance they will have carrier children

  • if one parent is a carrier and the other is affected, they will have affected children

    • 50% chance a child will be a carrier

    • 50% chance a child will be affected

  • if both parents have the condition, 100% of their children will also have the condition because they inherited mutated genes from each parent

What Genetic Condition are Caused by Autosomal Recessive Gene Variants?

  • common conditions include:

    • cystic fibrosis —

    • thalassaemia —

    • haemochromatosis —

    • Tay-Sachs disease —

  • genetic carriers do not show or develop any symptoms of health problems due to being a carrier

    • it is possible to test and determine whether someone is a carrier of certain recessive variants

  • there may be indications that someone may be a genetic carrier such as

    • having family members known to have a condition following an autosomal recessive pattern of inheritance

    • coming from certain ethnic or cultural backgrounds where the condition may be more common, the chance of this person being a genetic carrier would be higher than others

Source: VHS || Genetics, Autosomal Recessive

Intro

  • inheritance patterns illustrate disease transmission amongst generations of a family

  • those affected with AR disease have a disease allele on each chromosome

  • individuals affected with an AR disease can be traced through a family to determine which individuals are carriers and which are likely to become impacted

Development