Genetic Disorders and Genetic Testing © 2010 Project Lead The Way, Inc.Medical Interventions

Objectives and Understandings Analyze genetic testing results to predict phenotype Be able to answer the question – What is genetic testing?

Genetic Testing The use of molecular methods to determine if: someone has a genetic disorder will develop one is a carrier of a genetic illness Involves sampling a person’s DNA and examining the chromosomes or genes for abnormalities

Biology DNA/Genetics Review DNA has 4 base pairs Adenine – Thymine Cytosine – Guanine DNA has an alternating phosphate-sugar (deoxyribose) backbone DNA has a slightly negative charge

Biology DNA/Genetics Review Gene: a segment of DNA that contains the instructions for the production of a specific protein. Trait: a genetically determine characteristic Genotype: the actual allele combinations – the genes that determine the proteins produced The DNA code Phenotype: the physical (visual) representation of a trait What is seen

Biology DNA/Genetics Review If: R = protein produced allows person to roll tongue r = protein produced doesn’t allow person to roll tongue Then: What are the possible genotypes of a person who can roll their tongue?

Biology DNA/Genetics Review Key terms: Dominant – will always produce a certain phenotype Recessive – phenotype can only be seen when dominant gene is absent Autosomes – all chromosomes that are not the sex chromosomes Sex – Linked – all genes/traits located on the sex chromosomes

Biology DNA/Genetics Review If W = widow’s peak and w = no widow’s peak: What would the genotype be for: Homozygous dominant Homozygous recessive heterozygous

What are Genetic Disorders? Both environmental and genetic factors play a role in the development of disease. A genetic disorder is a disease caused by abnormalities in an individual’s genetic material. In this course, we will consider four different types of genetic disorders: Single-gene Multifactorial Chromosomal Mitochondrial

Single Gene Disorders Single gene disorders are caused by changes or mutations that occur in the DNA sequence of one gene. Diseases and disorders result when a gene is mutated resulting in a protein product that can no longer carry out its normal job.

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

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. Think back to PBS – what is sickle cell disease and what is life like for a person affected with this disorder?

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 Disorders Humans 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, are important in diagnosing chromosomal disorders.

Mitochondrial Disorders Mitochondria, the organelles in your cells that convert energy, also contain DNA. A mitochondrial disorder, a relatively rare type of genetic disorder is caused by mutations in non-chromosomal DNA of mitochondria. Mitochondrial DNA is unique in that it is passed solely from mother to child

Types of Genetic Testing and Screening

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. 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. Examples of carrier tests include those for 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.

Chosen Child Secrets of the Sequence – Chosen Child video Type in “Chosen Child” into Keyword search and view the “Chosen Child – Screening Genetic Content” video.

The Process of Preimplantation Genetic Diagnosis

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 quickly identify affected newborns in order to provide treatment and care from the start.

Activity Genetic Counselor Case File Project 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.