key of the various types of pedigree symbols.
Sarah and Robert Brown are the parents of one boy and two girls. The girls, Jillian and Melissa, are fraternal (non-identical) twins and are ten years old. The boy is 3 years old and is named Jack. All three children appear to be healthy, active, typical kids. Sarah and Robert recently received a letter in the mail from Jack’s preschool stating that he did not pass a hearing test offered by the school. The screening showed that Jack’s right ear didn’t respond to faint sounds. The school assured the Brown’s that the test result could be due to wax build up or a mild ear infection. Several months later during a follow-up screening Jack’s right ear still didn’t respond to faint sounds as it should. The Browns decided to take Jack to their pediatrician, Dr. Fairchild. The doctor ordered a more comprehensive set of hearing tests and determined that Jack had “unilateral sensorineural hearing loss”. Dr. Fairchild explained that unilateral means that only the right ear is affected while sensorineural means that the hearing loss is caused by problems in the inner ear or problems with the nerve supply to the ear. The doctor also explained that the hearing loss was likely congenital (present since birth) and that the loss was permanent but likely would not worsen. Dr. Fairchild suspected Jack’s hearing loss could be related to a genetic condition and that his reason for this suspicion was Jack’s unusually bright blue eyes. The doctor explained that both the ears and eyes are developed by the same germ layer in an embryo and thus an underlying genetic mutation might have caused both the unusual iris color as well as the hearing loss. Dr. Fairchild referred the Browns to a genetic counselor named Sylvia Armenta.
Dr. Sylvia Armenta sat down with the Browns to discuss Jack’s symptoms. Dr. Armenta suggested doing a pedigree with the Browns to help her learn more about the family’s health history. Dr. Armenta explained that the ectoderm is the tissue layer in a growing embryo that leads to the development of the ears, eyes, skin and nervous system. Like Dr. Fairchild, she suspected that Jack’s hearing loss and unusual eye color might be related to a genetic condition involving the ectoderm. Dr. Armenta asked the Browns if any other family members have any unusual characteristics with respect to skin, hearing or eyes. Sarah pulled up her shirtsleeve and pointed out that she had some small patches of skin that were not pigmented (pale). Sarah also confessed that she dyes her hair because it turned prematurely gray in her late 20’s. Sarah and Robert also mentioned that one of the twins (Jillian) has an iris with that is partially brown and partially blue. The parents said that Jillian also has pale skin patches similar to Sarah.
Dr. Armenta then asked Sarah and Robert about their family histories. Robert is one of four children; he has three sisters. As far as he knows neither he nor his sisters have any noticeable eye or ear problems. Robert’s parents are both still alive and aside from a history of high cholesterol on his Dad’s side of the family he doesn’t know of any genetic conditions in his family background. Sarah has one sister whose name is Daisy. Daisy has one son who seems to be a normal, healthy child with no unusual skin, eye or hearing characteristics. Daisy and Sarah’s father is still alive and seemingly very healthy at the age of 66. Their mother died in a car accident when they were very young and they don’t recall her having any major medical problems. Dr. Armenta suggested that Sarah bring in old family photographs in case some more family health history could be gleaned from the pictures. Dr. Armenta figured that since Jack’s symptoms seem to affect the ectoderm then perhaps related symptoms would be visible in the family photographs of his ancestors.
Sarah and Robert brought in several old photographs to their next appointment with Dr. Armenta. Photos of Robert’s family members didn’t demonstrate any usual skin, hair or eye characteristics. A photograph of Sarah’s mother showed that she had a small streak of pale hair on her forehead as well as striking bright blue eyes (similar to Jack’s eye color). There was also a more subtle characteristic in the photo of Sarah’s mother which Dr. Armenta described as “dystopia canthorum”. The doctor explained that the phrase basically means that the bridge of Sarah’s mother’s nose was slightly wider than average. An image of Sarah’s maternal grandfather as a young man showed that he had grayed prematurely and he also had the unique characteristic one blue eye and one brown eye. Dr. Armenta felt confident that all these unique family facial features were related to Jack’s hearing loss. The doctor decided to do some genetic testing on Jack to look for a mutation in the PAX3 gene. Dr. Armenta gently swabbed the inside of Jack’s cheek to collect some epithelial cells for genetic testing. While collecting the saliva sample she explained that the PAX3 gene is located on chromosome 2 and is responsible for controlling the development of the ectoderm which ultimately leads to proper development of the nervous system as well as hair and skin.
Several weeks later Dr. Armenta called with the results of the genetic analysis. She said that Jack did indeed have a mutation in his PAX3 gene…
draw a pedigree
To draw a pedigree, you will need to use the following symbols:
- Square: represents a male individual
- Circle: represents a female individual
- Filled in symbol: represents an individual with the condition being studied (in this case, Jack with unilateral sensorineural hearing loss)
- Half-filled symbol: represents an individual who is a carrier of the condition (has one copy of the gene mutation but does not exhibit symptoms)
- Line connecting two individuals: represents a marriage or partnership
- Horizontal line from parents to children: represents the offspring of the marriage or partnership
- Vertical line from the offspring: represents their children
Based on the information provided:
- Sarah (circle) and Robert (square) are the parents
- Jack (filled in square) is their son with unilateral sensorineural hearing loss
- Jillian and Melissa (circles) are fraternal twins
- Sarah has pale skin patches, premature gray hair, and patches of unpigmented skin
You can draw a pedigree to represent this information, along with any additional information provided regarding other family members. Make sure to include generations, siblings, and information about the specific characteristics of each individual.