Question

Sarah stared blankly at the blue paisley wallpaper. Her husband Mike sat by her side, bending and unbending a small paper clip.

“Sarah and Michael, it’s good to meet you,” welcomed the genetic counselor, as she entered the room. “I apologize for being late, but I was just meeting with another couple. Let’s see, you all are planning a pregnancy and you would like to know more about cystic fibrosis (CF) because of your family history.”

“Yes,” Sarah replied softly. “Mike and I met at a CF support group meeting a few years ago. He had a younger brother who died of cystic fibrosis, and I had a younger sister. We saw the painful lives they had—difficulty breathing, the constant respiratory infections. Although the treatments for CF are better now, we just don’t know if we can…” she trailed off.

“I can certainly understand your concern,” the genetic counselor responds. “That’s where I hope to help, by providing information about CF, your chances of having a child with CF and the options that are available. I’m glad that you came to see me before you became pregnant so we have the opportunity to explore all of your options.”

“To start, let’s go over what we know about your family history,” continued the genetic counselor. She pulled out a pad of paper, which she placed on the table in front of Sarah and Michael, and began to draw a series of circles and squares connected by lines to create their family tree.

“I’ve reviewed your family history paper work and it appears that you each have one sibling with cystic fibrosis and no additional family history of CF on either side of the family, right?”

“Yes,” said Sarah and Michael in unison. Sarah reports that she has one other sister that is healthy. Sarah’s father passed away at 65 from issues related to heart disease. Her mother is 66 and alive and well. Michael has fraternal twin brothers that are 16 years old. His parents are both healthy and in their 60’s. Michael’s family is of Ashkenazi Jewish descent and Sarah’s ancestors are from Ireland.

Question: Draw a pedigree showing the family history for CF in Sarah’s and Michael’s families. Be sure to distinguish between individuals with the disease, those that are carriers for the disease, deceased individuals and individuals who do not possess a copy of the disease allele. Mark the consultand for this case. Use appropriate pedigree nomenclature.

Answer 1

Cystic fibrosis is an autosomal recessive disorder. Disease will only occur if both the alleles are mutated for cystic fibrosis.

Parents of both michael and sarah do not suffer from CF. But for any of their child to be affected both of the parents have to be carriers.

Sarah and michael can either be carriers or homozygous normal.

Their probability to be normal is 1/2

Their child to be norma is 1/2 X 1/2 = 1/4

Sarah's pedigree Michad's pedigree I michael sarah o ora