MRS. STEWARTCENTRAL MAGNET SCHOOL

2.1.1 - Genetic Disorders and Genetic Testing

Family Bulletin

This week, James and Judy Smith have some unexpected news to share with their family. They just found out that they are expecting their third child. Now that the shock has worn off, they are excited to welcome a new member into their family. However, since Judy is in her forties, her pregnancy is considered high risk. The doctor has suggested genetic testing and screening to monitor the pregnancy and to identify any potential complications with the fetus. James and Judy never had to make these kinds of decisions with their first two kids. The idea of learning too much about their child before he or she is born is a bit scary, so they ask their doctor for more information.

 

Family Bulletin Continued

Mr. Smith’s brother Aaron and his new wife Gina are elated by Judy and James’ news as they have decided that they are ready to start their own family. They are both young, 28 and 26, respectively, but they decide to see a doctor before they start trying to conceive a child. Gina’s brother and his wife have a five-month-old son who has just been diagnosed with cystic fibrosis. Gina knows the disease has a genetic component, so she wants to learn more about her risk of passing this gene on to her child. Her doctor assures her that simple genetic testing can identify whether or not she and Aaron are carriers for the disease, but Gina and Aaron have many unanswered questions. They never thought that deciding to have a baby could be so complicated. The doctor has suggested that Gina and Aaron discuss their case with a genetic counselor.

 

Family Bulletin Continued

The two couples, James and Judy, and Aaron and Gina, are at different stages in their lives, but both couples face important decisions regarding the ability to look into our cells and test and screen DNA. What types of things can we learn about our children before they are even born? How much would you want to know about your own genes? Follow the Smith brothers as they explore the science and the personal side of genetic testing and screening.

Genetic Testing Pre-Survey

Take the genetic testing survey and evaluate your opinion for each of the questions based on what you already know

Objectives

Evaluate the relationship between DNA codes and the proteins produced Understanding that changes in DNA lead to

changes in proteins, which could produce a genetic disorder/disease.

Analyze genetic testing results to predict phenotype

What are Genetic Disorders?

Genetic disorder - a disease caused by abnormalities in an individual’s genetic material.

Both environmental and genetic factors play a role in the development of disease.

Biology Review

What is a genotype? The actual genetic makeup of an organism (the true

“genes” for a specific trait – the actual alleles)

What is a phenotype? The physical expression of a trait

R = able to roll tongue; r = not able to roll tongue Which one is dominant? Which one is recessive?

Biology Review

Using R = can roll tongue, and r = can’t roll tongue:◦ Write a homozygous dominant genotype ◦ Write a homozygous recessive genotype ◦ Write a heterozygous genotype

Why is a heterozygous referred to as a carrier

How many pairs of chromosomes do we have?◦ 23

What is the 23 pair called? ◦ Sex chromosomes

What is an autosome?◦ Every chromosome that is NOT a sex chromosome

RR

rrRr

Genetic Disorders

Gene- a segment of DNA that contains instructions for the production of a protein.

Diseases and disorders result when a gene is mutated resulting in a protein product that can no longer carry out its normal job.

Scavenger Hunt

In this course, we will consider four different types of genetic disorders:

Single-gene Multifactorial Chromosomal Mitochondrial

Fill in your student response sheets by finding the definitions and examples listed around the room, matching them to the correct disorder on your notes page.

Use the information provided to fill in your notes page

Single Gene Disorders

Single gene disorders are caused by changes or mutations that occur in the DNA sequence of one gene.

Single gene disorders are inherited in recognizable patterns: Autosomal dominant Autosomal recessive Sex linked

Multifactorial Disorders

Multifactorial disorders are caused by a combination of environmental factors and mutations in multiple genes. Development of heart disease is associated with

multiple genes, as well as lifestyle and environmental factors.

Different genes that influence breast cancer development have been found on chromosomes 6, 11, 13, 14, 15, 17 & 22.

Many of the most common chronic illnesses are multifactorial.

Chromosomal DisordersHumans have 46 chromosomes in their body

cells. 44 autosomes 2 sex chromosomes

Because chromosomes carry genetic information, problems arise when there are missing or extra copies of genes, or breaks, deletions or rejoinings of chromosomes.

Karyotypes - pictures of the paired chromosomes of an individual important in diagnosing chromosomal disorders.

Mitochondrial Disorders

Mitochondria (the organelles in your cells that convert energy) contain DNA.

A mitochondrial disorder is caused by

mutations in nonchromosomal DNA of mitochondria. a relatively rare type of genetic disorder

Mitochondrial DNA is unique in that it is passed solely from mother to child

Genetic Testing and Screening

Objectives

Evaluate the relationship between DNA codes and the proteins produced Understanding that changes in DNA lead to changes in

proteins, which could produce a genetic disorder/disease.

Analyze genetic testing results to predict phenotype

What is Genetic Testing?

Genetic testing looks at genotype to determine if someone has a genetic disorder, will develop one, or is a carrier.

Review Question

A man and a woman are both carriers for sickle cell disease, an autosomal recessive trait. What is the risk of their having an affected child?

S = No sickle cell; s = sickle cell disease

Draw a punnett square to find answer

Answer

Each parent is heterozygous for the condition and has the genotype Ss (where “s” is the recessive sickle cell allele). Each parent passes one allele to the child, so there is a 25% chance that the child will have sickle cell disease.

Carrier Screening

Carrier screening determines whether an individual carries a copy of an altered gene for a particular recessive disease even though they do not show the trait phenotypically. Essentially this tells if a person is heterozygous for a

particular trait

Carrier screening is often used if a particular disease is common in a couple’s ethnic background or if there is a family history of the disease. Example: Tay-Sachs disease or sickle cell disease.

Preimplantation Genetic Diagnosis (PGD)

PGD is used following in vitro fertilization to diagnose a genetic disease or condition before the embryo is implanted in the uterus. A single cell is removed from an embryo and

examined for chromosome abnormalities or genetic changes.

Parents and doctors can then choose which embryos to implant.

Secrets of the Sequence – Chosen Child video http://www.youtube.com/watch?v=a5SB9t7m0V

s

Fetal Screening/Prenatal Diagnosis

Prenatal diagnosis allows parents to diagnose a genetic condition in their developing fetus.

Techniques such as amniocentesis, chorionic villi sampling (CVS), and regular scheduled ultrasound allow parents to monitor the health of the growing fetus.

Newborn Screening

The most widespread type of genetic screening, newborn screening is used to detect genetic or metabolic conditions for which early diagnosis and treatment are available.

State tests for newborns typically screen anywhere from 4 to over 30 genetic or metabolic disorders. Testing protocol and mandates vary from state

to state.The goal of newborn screening is to

identify affected newborns quickly in order to provide quick treatment and care.

Activity 2.1.1

In this activity, you will assume the role of a genetic counselor and meet with clients faced with difficult decisions regarding genetic disorders and genetic testing.

Your goal is to effectively explain the disease or disorder to your clients as well as to outline potential options for genetic testing and screening and overall management of disease.