Genetic Disorders and Genetic Testing

1. Genetic Disorders and Genetic Testing Mrs. Stewart Central Magnet School

2. 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.

3. 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?

4. 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 rr Rr

5. 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. • In this course, we will consider four different types of genetic disorders: • Single-gene • Multifactorial • Chromosomal • Mitochondrial

6. 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

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

8. 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

9. 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.

10. 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.

11. 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 • important in diagnosing chromosomal disorders.

12. 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

13. Types of Genetic Testing and Screening

14. 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.

15. 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=a5SB9t7m0Vs

16. 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.

17. 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.

18. 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.