Things to do before we start class… Take out Prenatal Development Worksheet
Lesson 2 Objectives: Summarize the process of heredity. Define terms associated with heredity. Identify some genetic disorders.
Heredity is the passing of physical traits from parents to their children What traits did you inherit from your parents? (ex. Eyes, height) Inherited traits can also be influenced by the environment (ex. poor nutrition limits growth during childhood)
Chromosomes Thread-like structures within the nucleus (control center) of each cell in our body They carry codes for inherited traits Most cells in the human body contain 46 chromosomes arranged in pairs of 23
Genes Sections of chromosomes are called genes They are the basic units of heredity They appear in pairs 1 gene from each pair is inherited from each parent 1000s of genes are found in every cell in your body
DNA DNA is the chemical unit that makes up chromosomes Deoxyribonucleic acid is basis of all living things Made up of chemical building blocks arranged along single molecule Several molecules link in a strand to form a DNA sequence called genetic code
DNA A child carries a combination of DNA sequencing from both parents Identical twins share the same DNA pattern
Genetics and Fetal Development Chromosomes from a sperm and egg unite to carry the hereditary traits from parents –A sperm and egg have 23 chromosomes –After fertilization, the zygote will have 46 chromosomes (23 from each parent) –A zygote divides many times, ultimately producing trillions of cells that make up the human body –Between each cell division, each chromosome in the nucleus of the cell copies itself, producing 2 sets of 46 chromosomes –The cell then divides and the 2 sets of chromosomes separate –Each new cells then contains one complete set of the 46 chromosomes that are identical to the ones found in the first cell of the zygote
2 Types of Genes Recessive –The traits of the recessive genes usually appear only when the dominant genes are not present Dominant –The traits of the dominant genes generally appear in the offspring when they are present
Genes and Gender One pair of chromosomes determines gender –Females have 2 x chromosomes that look alike –Males have a shorter y chromosome and a longer x chromosome –Who do you think determines the sex of a baby when the sperm and egg unite? The male or female?
Genetic Disorders Caused partly or completely by a defect in genes Common ones include: –Sickle-cell anemia –Tay-sachs disease –Cystic fibrosis –Down syndrome –Hemophilia
Sickle-cell anemia –RBC’s become C- shaped, stiff and sticky –Don’t move through blood easily and get stuck in vessels –Block blood flow to limbs and organs causing pain, infections, and organ damage
Tay-Sachs disease –Harmful quantities of a fatty acid derivative accumulate in the nerve cells of the brain –Infants appear normal the first months and then deteriorate in mental and physical abilities
Cystic fibrosis –Inherited disease of the sweat and mucus glands –Causes mucus to be thick and sticky - clogs lungs & makes it easy for bacteria to grow
Down syndrome –Extra genetic material causes delays in the way a child develops often leading to mental retardation
Hemophilia –Rare inherited disorder in which blood does not clot normally –Usually occurs in males –May bleed for a long time after injury or accident –May also bleed into joints (painful and leads to arthritis)
3 Methods of Identifying Health of the Child 1. Amniocentesis –A syringe is inserted into pregnant woman’s abdomin3 and into the amniotic fluid surrounding the fetus –Some fluid is removed to study chromosomes, body chemistry and determine sex of child –Done at 16-20 weeks
3 Methods of Identifying Health of the Child 2. Ultrasound test –Sound waves are used to project light images on a screen –Waves act like an echo and form image of fetus –Used to determine position of fetus and number of fetuses
3 Methods of Identifying Health of the Child 3. Chorionic villi sampling –CVS is a procedure in which a small piece of membrane is removed from the chorion, a layer of tissue that develops into the placenta –Can be examined for genetic disorders or to determine the age and gender of child –Usually done around the eighth week of fetal development
Battling Genetic Diseases Gene therapy – process of inserting normal genes into human cells to correct genetic disorders –Scientists think that if defective gene is replaced with normal gene, cells can begin producing normal gene Genetic counseling –Can guide families about risks and treatments Genetically engineered drugs –Genes used to treat diseases are not inserted directly into humans but placed into other organisms causing it to produce the substance that can be used to treat human diseases and disorders
Genetic Engineering Can you speculate why this is such a controversial topic and what ethical concerns it involves?
Did you master the Ch 20 lesson 2 objectives? Summarize the process of heredity. Define terms associated with heredity. Identify some genetic disorders.