Genetics is the study of inheritance, which helps explain how certain traits are passed from parents to children and DNA has long been called the “blueprint” of how living organisms are built because it contains all of the genetic material needed to make the organism. In short, traits (or personal characteristics) are passed down from parents via genes, which are small segments of DNA. Genes are located on chromosomes, which are comprised of hundreds to thousands of genes. Each gene also contains different variations (e.g., dimples or no dimples), which are called alleles. Every cell in the human body contains 23 pairs of chromosomes (23 from their mother and 23 from their father). Some alleles may be dominant, while some may be recessive, which merely describes how likely it is that a particular trait will be expressed.
Since you both have the disorder and it is autosomal dominant, this means that only one inherited copy is needed in order to have the disorder. Also, since you already have one child without the disorder, this means that both of you only carry one copy of the disorder [drawing chart]. To make it more clear, your makeup for this disorder looks like this: Aa, Aa (with A representing the disorder and a representing lack of the disorder). With this combination, we can have four scenarios for your children: AA, Aa, Aa, and aa. As you can see, there is a 25% chance of your child not having the disorder (aa) and a 75% chance of your child having the disorder. This chance is the same each time you have a child, irrespective of any other children you already have.
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If you are both carriers of CF (and don’t actually have it) and it is an autosomal recessive disorder, this means that in order to actually have the disorder, you need to acquire both defective copies of the gene. This chart will better help explain it. Since you are only carriers, your makeup look like this: Cc, Cc and the possible combinations for your children are: CC, Cc, Cc, and cc. In this case, your children have a 25% chance of inheriting the disorder because if you each pass on the “a,” then your child has inherited both copies of the disorder. They have a 25% chance of not even being carriers (CC) and a 50% chance of being carriers (Cc), like you.
Based on the pedigree chart, the disorder is autosomal dominant because it occurs in children about 50%, does not skip generations, and when there is an affected parent, there is always at least one affected child. Also, in the second generation, there is a scenario where both parents are unaffected and have three children that are unaffected. If the disorder was recessive, it would be likely that at least one child would be born to even unaffected parents (as in the case of CF).
