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Download Ch 14 Notes - The Human Genome
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Chapter 14 - The Human Genome 14-1 Human Heredity • The children in this family have some traits that are similar to their mother’s and some that are similar to their father’s. • Can you predict chin shape? • Procedure – Two parents with cleft chins, both heterozygous for cleft chin (Cc), have three children with cleft chins. The parents are sure that their fourth child will not have a cleft chin. Draw a Punnett square to see if this is possible. • Determine the probability that the fourth child will have a cleft chin. _________ Human Heredity • Human Chromosomes – Make us who we are. – This is the genetic information (DNA) which is inside the human cell. • To look at these chromosomes, biologists, photograph cells in mitosis. – Mitosis is when the cell nucleus divides and the chromosomes are easier to see. – Biologists then take these photographs and group them together in pairs. – This picture of chromosomes arranged in this way is called a karyotype Karyotype • The human body contains 46 chromosomes – 23 (sperm) – 23 (egg) • Together this forms a diploid zygote – 46 total chromosomes Sex Chromosomes and Autosomes • Sex chromosomes – Only 2 of the 46 – Determine if someone is male or female – Female: XX – Male: XY • Autosomes – Remaining 44 chromosomes Human Traits • Human traits are inherited – Gregor Mendel • Pedigree chart – A pedigree shows a relationship within a family – A pedigree chart follows one specific trait in a family Cleopatra’s Pedigree Chart Russian Royal Family Pedigree Chart Polygenic • Some traits are actually polygenic – Controlled by two or more genes • Shape of your eyes • Shape of your ears • Eye color Other Trait Influences • Environment • Nutrition • Exercise • Your parents might both be 6 feet tall, but if they don’t feed you, you are unlikely to grow to be 6 feet tall. Human Genes • Our complete set of genetic information is our genome – 30,000 genes • Blood Group Genes: – Knowing a person’s blood group is critical because using a wrong blood type could be life threatening – Rh – ABO • Are two genes that are part of your blood type Rh • Rhesus Monkey” • 2 alleles that determine blood type – Rh+ is dominant & Rh- is recessive • A person with 2 positive alleles is Rh+ • A person with a positive and a negative allele is RH+ • A person with 2 negative alleles is Rh- ABO • There are 3 alleles that determine blood type – IA, IB and i • Two of these alleles are codominant and one is recessive. • Blood type is dependant upon what the antigens are on the surface of the red blood cells • Type A blood: lAlA, or IAi • Type B blood: IBIB or IBi • Type AB blood: IAIB • Type O blood: ii • Based on what you know of blood types; which one of Mr. & Mrs. Lopez’s four kids must have been adopted? _____________ Recessive Alleles • Studying genetic disorders have helped us understand how human genes work • Many of these disorders are caused by recessive alleles Phenylketonuria (PKU) • People with this disorder lack the enzyme needed to break down Phenylalanine • Causes: – A build-up of phenylalanine in tissues – Mental retardation – Can be controlled by a special diet – All babies in US are tested for this at birth Tay-Sachs Disease • Nervous system breakdown • Infant death Albinism • Lack of pigment in skin, hair, and eyes Cystic Fibrosis • Excess mucus in lungs, digestive tract, and liver • Susceptibility to infections • Death in early adulthood if not treated Galactosemia • Inability to digest the sugar galactose. • Causes mental retardation, eye and liver damage Cystic Fibrosis Dominant Alleles • Not all genetic disorders are caused by recessive alleles • If you have a dominant allele for a genetic disorder, it will be expressed even if you also have a normal recessive allele – Achondroplasia – Huntington’s disease – Hypercholesterolemia Achondroplasia • Dwarfism Huntington’s Disease • Mental deterioration and uncontrollable movements Hypercholesterolemia • Excess cholesterol in blood • Heart disease Gene Expression • In certain diseases, a small change in the DNA of a single gene affects the structure of a protein, causing a serious genetic disorder – Cystic fibrosis – Sickle cell anemia Sickle Cell Anemia • Abnormal hemoglobin produced because of a single amino acid change in the hemoglobin protein • Causes the RBC’s to deform which causes clogging in the capillaries Sickle Cell Anemia 14-2 Human Chromosomes Sex-Linked Genes • Because the X and Y chromosomes determine sex, genes located here are said to be sex-linked genes • More than 100 sex-linked genetic disorders have been mapped to the X chromosome • Males have just one X chromosome. Thus, all X-linked alleles are expressed in males, even if they are recessive Sex-Linked Genes • Genes that are found on the X or Y chromosome. • More genes are found on the X chromosome than the Y Colorblindness • Three genes associated with color vision are found on the X chromosome • Males are more often colorblind because they only have one X chromosome Colorblindness Test Colorblindness • All X-linked alleles are expressed in males even if they are recessive Examples of X-linked Recessive Disorders • Hemophilia: blood-clotting disorder • Duchenne Muscular Dystrophy • Ichtyosis: scaly skin • Norrie Disease: abnormal growth of retina • Rett Syndrome: mental retardation Hemophilia Duchenne Muscular Dystrophy X-Chromosome Inactivation • Females have 2 X chromosomes and males only one. What to do? • In all female cells, one X chromosome is randomly shut off. • This causes some interesting problems if one X chromosome has a mutated gene Chromosomal Disorders • Get too many or too few copies of a chromosome • Caused by non-disjunction during meiosis • Exs. Down’s Syndrome: Trisomy 21 Turner’s Syndrome: X_ Klinefelter’s Syndrome : XXY Down’s Syndrome Turner Syndrome Kleinfelter Syndrome 14-3 Human Molecular Genetics Human DNA Analysis • Genetic tests are now available for hundreds of disorders. • This can allow prospective parents to determine if they are carrying recessive alleles for a disorder. DNA Fingerprinting • DNA is analyzed of by separating it into fragments • This reveals a series of DNA bands of various sizes • A pattern of bands is produced that can be distinguished from any other individual in the world (except for an identical twin). • DNA samples can be obtained from blood, sperm, and hair strands that have tissue at their base. DNA Fingerprinting The Human Genome Project • The Human Genome Project was an attempt to sequence all human DNA • In June 2000, scientists announced that the Human Genome was complete. • There is open availability of nearly all its data. • You can use the Internet to read the latest genome data. Gene Therapy • Gene Therapy is the process of changing the gene that causes a genetic disorder • In gene therapy, an absent or faulty gene is replaced by a normal, working gene • This way, the body can make the correct protein or enzyme it needs, which eliminates the cause of the disorder Gene Therapy Ethical Issues • What will happen to the human species of we could design our bodies? What would be the consequences? • Society will have to develop a thoughtful and ethical consensus of what should and should not be done with the Human Genome.