Download Genetic Disorder

1
Name _________________________
The Problem
You are a genetic counselor. Your boss has recently met with a
family whose child/family member has been diagnosed with a genetic
disorder. You have been assigned the task of preparing an
informational brochure and oral presentation on this disorder.
Types of Genetic Disorders
There are several types of genetic disorders. One of your jobs will be to explain how the
genetic disorder for the disease you chose is inherited. Genetic disorders fall into three basic
categories:
• single gene defects
• chromosomal disorders
• multifactorial
Single gene disorders:
A single gene disorder is one that is determined by a change in one of the alleles such as “A” and
“a” in some of the crosses we have done in class. There are five basic types of single gene
inheritance:
• Autosomal dominant
• Autosomal recessive
• X-linked dominant
• X-linked recessive
• Maternal (mitochondrial) inheritance
Autosomes are the first twenty -two chromosomes pairs of chromosomes found in a human
karyotype. Therefore, all of the chromosomes are autosomes (1-22) except the two chromosomes
that determine one’s sex (X and Y). There are not many genes on the Y chromosome, so there are
not many genetic disorders found on the Y chromosome. There are several genes and therefore,
several genetic disorders found on X chromosome. Genetic disorders found on the X chromosome
are called “sex-linked” disorders. We will not be discussing maternal inheritance at this time. None of
the genetic disorders that were assigned (chosen) are due to maternal inheritance.
In X-linked inheritance (or sex-linked inheritance), the genes are located on the X
chromosome. X-linked recessive inheritance occurs at a much higher rate in males than in females
because only one defective gene on the X chromosome is necessary for a male to inherit the
disorder. There is no comparable gene on the Y chromosome to cover or mask the defective gene
found on the X chromosome.
Very few disorders are X-linked dominant. Only one defective gene found on the X
chromosome is necessary for a person to inherit an X-linked dominant disorder. One of the genetic
disorders on your list is X-linked dominant.
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Chromosomal disorders
In a chromosomal disorder, the genetic disorder is not due to a single gene, but rather an
excess (trisomy) or deficiency (monosomy) of the genes contained on whole chromosomes or parts
of chromosomes. Several disorders fall into this category.
Multifactorial disorders
Many human disorders fall into this category. In multifactorial inheritance, many genes may
contribute to the genetic disorder as well as environment factors. Some of these disorders fall under
the textbook categories of polygenic inheritance and environmentally influenced.
YOUR JOB: BIOLOGY EXPECTATIONS
Always keep your audience in mind
Once you have read about your genetic disorder, one of your first and most important jobs will be
to decide how the genetic disorder is inherited (see previous page). You should be able to:
1. EXPLAIN how the genetic disorder you chose is inherited. Your explanation should be more
than autosomal recessive, autosomal dominant, X-linked recessive, etc. You need to make
your explanation crystal clear to your audience (a family who has a family member with the
genetic disorder). Remember, your audience probably has no idea what these words mean.
2. What chromosome or chromosomes is/are affected?
3. IF APPROPRIATE, use a PUNNETT SQUARE in your brochure and/or with your oral
presentation. Make sure you include an explanation in your brochure and/or with your oral
report. Use a poster board for your oral presentation. The audience needs to be able to see
your Punnett Square. Include all five steps (determining the cross, determining the gametes,
the Punnett square, genotypes, and phenotypes).
4. What is the likelihood of another family member getting the genetic disorder? Explain why!!!
The gene or genes that cause the genetic disorder is/are different from the “normal” gene(s) that
do not cause the genetic disorder.
5. You need to explain how the gene(s) is /are different and what effect has the different gene or
genes caused. Is there a different chemical or protein produced by the “different” gene? How
does the change in the gene cause the genetic disorder?
6. Make sure you do not use terminology that your audience (the family) would not know. Explain
or define what the BIG words mean. Definitions or explanations should include words the
average person would know. Remember—we don’t know anything about genetics or
chromosomes, or genes, etc.
You are responsible for holding onto this information sheet and keeping it neat.