What does genetic inheritance mean?
28.NOV.2023
Written by Anna Sanniti
Reviewed by Wendi Gill, CGC
Genetic inheritance is what controls the characteristics, also known as traits, of all living things. We each inherit genes from our parents, and the combination of these genes is what makes us unique. This is why members of the same family have similar characteristics.
In this article, we will discuss:
How genes are passed down from parents to their offspring.
What are dominant and recessive conditions?
How genetic inheritance contributes toward hereditary conditions.
How are genes passed down from parents to their offspring?
Remember that we each inherit an entire genome from each of our parents, stored as 23 pairs of chromosomes in each of our cells. This happens when a sperm cell combines with an egg cell, creating the complete instructions to make a new person. The chromosome from the mother and the chromosome from the father have the same genes, and thus we have two copies of each our our genes. The two copies of the gene may have different DNA sequences due to genetic mutations, also known as genetic variants. If a genetic mutation is expected to change the DNA sequence in a way that causes a person to have or be at risk of developing a certain genetic disorder or disease then it is referred to as a pathogenic variant (or disease-causing change).
What are dominant and recessive conditions?
A hereditary condition is a condition or disease, that is passed down in families. Hereditary conditions can be inherited in various ways including through autosomal dominant inheritance or autosomal recessive inheritance. The term autosome describes a chromosome that is not one of the sex chromosomes.
Some hereditary conditions are inherited in an autosomal dominant nature, meaning that for an individual to be at risk of developing the condition they must have a pathogenic variant on only one copy of their two genes. Examples of conditions that are inherited in an autosomal dominant nature include hereditary breast and ovarian cancer syndrome and Lynch syndrome, which are both inherited cancer predisposition syndromes. If an individual has an autosomal dominant condition, then each of their first-degree relatives (children, parents, and siblings) has a 50% chance of also having the mutation.
If a condition is autosomal recessive, then an individual must have a pathogenic variant on both copies of their two genes to be affected by the condition. Individuals who are carriers for a recessive condition (meaning that they only have a pathogenic variant on one copy of their genes), are not expected to have symptoms of disease and typically are not aware they are carriers unless they had genetic testing.
Let’s recap
Genetic inheritance is what controls the characteristics of all living things.
We each inherit an entire genome from each of our parents, stored as 23 pairs of chromosomes in each of our cells.
The chromosome from the mother and the chromosome from the father have the same genes, however, they can have different versions of these genes
Hereditary conditions are conditions or diseases that are passed down in families.
If a condition is autosomal dominant, then an individual only needs a pathogenic variant to be present on one copy of the gene for that person to be at risk of developing the condition. Examples of dominant conditions include familial hypercholesterolemia, hereditary breast and ovarian cancer syndrome, and Lynch syndrome.
If a condition is autosomal recessive, then an individual needs a disease-causing variant to be present on both of their alleles to be at risk for the condition.
References
1. National Human Genome Research Institute Educational Resources. Mendelian Inheritance. Online: genome.gov 2. National Human Genome Research Institute Educational Resources. Autosomal Recessive Disorder. Online: genome.gov 3. National Human Genome Research Institute Educational Resources. Autosomal Dominant Disorder. Online: genome.gov