Biology - Chp14 - Human Heredity - Notes


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Biology - Chp14 - Human Heredity - Notes

  1. 1. Chapter 14Human Heredity
  2. 2. 14-1 Human Heredity• Scientists once knew much less about humans then about other “model” organisms such as fruit flies and mice• With the completion of the Human Genome Project scientists are on verge of understanding human genetics at least as well as they understand that of some other organismsHuman Chromosomes• To analyze chromosomes, cell biologists photograph cells in mitosis• Chromosomes are fully condensed and easiest to see during ____________________Karyotype - ____________________________________________________________________________________________________________________________________• We all began life when a haploid sperm fertilized a haploid egg carrying just ________ chromosomes each.• The _________________________ zygote or fertilized egg contained the full complement of __________ chromosomesSex chromosomes - ______________________________________________________________________________________________________________________________Females: ___________Males: _____________• The regular 44 chromosomes are known as __________________________________ 2
  3. 3. Q: Why are males + females born in a roughly 50:50 ratio?A: All egg cells carry a single _______ chromosome. However, half of all sperm carry an_______ chromosome, the other half carry a ________ chromosomeHuman Traits• In order to apply Mendelian genetics to humans, biologists must identify an inherited trait controlled by a single gene• Then, they have to study how the trait is passed from one generation to the nextPedigree - _______________________________________________________________________________________________________________________________________ 3
  4. 4. • Most human traits are not coded for by single genes• Also, many traits are strongly influenced by environmental factors o Ex.) average height has increased 10cm in the United States and Europe since 1800’sPolygenic traits - _________________________________________________________Human GenesThe human genome - ______________________________________________________• Includes tens of thousands of genes• Until recently the identification of a human gene took years of work• Humans aren’t easy test subjects o o oBlood Group Genes• A number of genes are responsible for human blood groups, but the best known are the ABO and Rh blood groupsRh blood group Rh is an antigen found in the blood of• Single gene with two alleles about 85% of all people; these people are said to be Rh positive. The rest of theRh + (dominant) population is Rh negativeRh - (recessive)Recessive alleles• Many human genes have become known through the study of genetic disordersQ: How do scientists identify recessive alleles that cause these disorders?A:PKU – phenylketonuria• Lack enzyme needed to break down phenylalanine• Found in milk and other foods• If newborn has PKU, phenylalanine may build up in the tissues during severe mental retardation• If newborns are tested early, they can be placed on a low phenylalanine diet which prevents most of the affects• PKU is caused by a recessive allele carried on chromosome 12 4
  5. 5. Tay Sachs• Autosomal recessive• Found mostly in Jewish families of central and eastern European ancestry• Results in nervous system breakdown and death in the first few years of life• There is no treatment, but there is a test prospective parents can takeDominant Alleles• Not all genetic disorders are caused by recessive allelesAchondropasia – dwarfism• Never reach 4 feet 4 inches• Cartilage forms in such a way that the arms and legs end up being disproportionately short• 1 in every 10,000 is affectedHuntingtons• Progressive loss of muscle control and mental function until death occurs• People with disease show no symptoms until they are in their 30’s and 40’sCodominant Alleles• Sickle cell disease• Affects 1 in 500 African AmericansFrom Gene to MoleculeCystic Fibrosis (CF)• Most common among people whose ancestors come from northern europe• Caused by a recessive allele on chromosome 7• Produce a thick heavy mucus that clogs their lungs and breathing passageways• Serious digestive problems• Only half survive into their 20’s 5
  6. 6. Sickle Cell Disease• Characterized by the bent and twisted shape of the red blood cell• Sickle shaped red blood cell tend to get stuck in the capillaries• Produce physical weakness and damage to the brain, heart and spleen• Sometimes fatal• Change in _______________________ DNA base• This change inserts amino acid ______________________ in place of __________________________________• Hemoglobin molecules stick together and form long chains that produce the characteristic shape of sickled cellsQ: Why do so many African Americans carry the sickle cell alleleA: Many African Americans have ____________________________________________ancestry where _________________________ is a serious problem• People who are heterozygous for the sickle cell allele don’t get sickle cell and they don’t get malaria Malaria and the Sickle Cell Allele The map on the left shows where malaria is common. The map on the right shows regions where people have the sickle cell allele. 6
  7. 7. Dominant or Recessive• It all depends on the nature of a genes protein product and its role in the cellEx.) In CF, one copy of the normal allele can supply cells with enough chloride channelproteins to function therefore the normal CF allele is considered ____________________ 7
  8. 8. Name ____________________________________ Date __________________ Per ____ 14-1 Section Review1. What are sex chromosomes? What determines whether a person is male or female?2. Using an example, explain how a small change in a person’s DNA can cause a genetic disorder.3. How does studying genetic disorders such as PKU help biologists understand normal alleles?4. What are some problems biologists face in studying human inheritance?5. Critical Thinking Predicting If a woman with type O blood and a man with type AB blood have children, what are the children’s possible genotypes? 14-2 Human Chromosomes 8
  9. 9. • A human diploid cell contains more than ____________________________ nucleiotide pairs of DNA• Despite its size, all of this information is neatly packed into the 46 chromosomes present in every diploid cell• Each chromosome is like a library containing hundreds or even thousands of books• Biologists are many decades away from mastering the contents of these books, but they are learning just how many books there are and what they deal withSex Linked Genes• Genes located on the sex chromosomes• Most found on the ________ chromosomeColorblindness • Gene associated with color vision are located on the X chromosome • Affects 1 in 10 males • Affects 1 in 100 femalesQ: Why the difference between the sexes?A: Males have ____________________________ X chromosome.Thus, all X-linked alleles are expressed in males, even if they arerecessive• In order for a woman to be affected, there must be __________________________ of the alleleEx.) What is the probability of a normal vision male and a femalewho is a carrier for the color blind trait having a child that is colorblind?Hemophilia 9
  10. 10. • A protein necessary for normal ________________________________ is missing• 1 in 10,000 males• People with hemophilia can bleed to death from minor cuts and may suffer from internal bleeding• Treated with normal clotting factorsDuchenne Muscular Dystrophy• Results in progressive weaking and loss of skeletal muscle• Rarely live past early adulthood• In the U.S. 1 in 3000 males is born with Duchenne muscular dystrophy• Caused by a defective version of the gene that codes for a muscle proteinX-Chromosome InactivationQ: If all you need is one X chromosome, what happens to the extra X chromosome infemales?A:• Same in cats, that’s why you can have cats with 3 different colors o Fur color is on the X chromosome. Some areas have one color switched on, and others its switched off Calico Cat: This cat’s fur color is controlled by a gene on the X chromosome. 10
  11. 11. Chromosomal DisordersNondisjunction - __________________________________________________________________________________________________________________________________• If nondisjunction occurs, ________________________________________________________________________________________________________________________________________________________________________________________________Disorders of Chromosome NumbersDown Syndrome• When nondisjunction happens and a baby is born with _________________________ of __________________________________________• Trisomy 21• 1 in 800 in U.S.• Mild to severe retardation• Susceptible to many diseases• Increased frequency of birth defects 11
  12. 12. Sex Chromosome DisordersTurners Syndrome (female)• Only inherit one ___________________________________• Genotype = ___________• Women with Turner syndrome are sterile, their sex organs don’t properly develop at pubertyKlinefelters Syndrome (males)• Inherit ___________________________________________• Genotype = ________________• The extra X interferes with meiosis and usually prevents them from reproducing• Some cases _______________________________________• These abnormalities show us the role of Y in sex determination o Even in combination with several X’s, the Y makes them male• But if this Y is absent, the embryo develops into a female 12
  13. 13. Name __________________________________ Date __________________ Per ______ 14.2 Section Review1. Why are sex-linked disorders more common in males than in females?2. How does nondisjunction cause chromosome number disorders?3. List at least two examples of human sex-linked disorders.4. Describe two sex chromosome disorders.5. Critical Thinking Comparing and Contrasting Distinguish between sex-linked disorders and sex chromosome disorders. 13
  14. 14. Extra Credit Animating Nondisjunction Make a flip book to animate nondisjunction during meiosis. First, make a series of 6 to 10 drawings that gradually show the process of nondisjunction. Then, put the process in motion by flipping the pages with your thumb. 14.3 Human Molecular GeneticsHuman DNA Analysis• Way too much DNA to search through• Biologists search the volumes of the human genome using DNA sequencesTesting for Alleles• If two prospective parents suspect they might be carrying recessive alleles for a genetic disorder they can now get a test to determine the risk of passing that trait on to their children o Use labeled DNA probes to detect specific sequences found in disease causing alleles o Looking at changes in restrictive enzyme cutting sites o Looking at differences in lengths of allelesDNA Fingerprinting• Because the human genome is so complex, no individual is exactly like any otherDNA fingerprinting - ______________________________________________________________________________________________________________________________________________________________________________________________________• Used to settle paternity disputes• Convict criminals and overturn convictionsThe Human Genome Project• Advances in DNA sequencing technologies at the close of the twentieth century made it possible to begin sequencing entire genomes• At first, biologists worked on small genomes of viruses and bacteria 14
  15. 15. • In 1990, scientists in the United States and other countries began the Human Genome Project o An attempt to sequence all human DNA• In 2000 scientists announced that the DNA sequence of the human genome was essentially complete• We estimate as little as 31,000 genes o Fruit fly – 14,000 o C. elegans worm 20,000• Now the task is to figure out how so few genes make an organism as complex as usSearching for genesPromoter – ______________________________________________________• Researchers are looking for genes that provide useful clues to some of the basic properties of life• Also looking for genetic information that may be useful in developing new drugs and treatment of diseaseA Breakthrough for Everyone• Data from the human genome project is posted on the internet on a daily basis• www.genome.govGene Therapy• The most obvious use of info about the human genome would be to cure genetic disorders by gene therapyGene therapy - ___________________________________________________________________________________________________________________________________ • Not always been successful, no lasting cure yet 15
  16. 16. Ethical Issues in Human Genetics• There are many questions which science will rapidly force society to come to grips with• If it’s just as easy to manipulate genes for personal preference then it is to cure a disease should we do it?• Our society will have to develop a thoughtful and ethical conscious of what should and shouldn’t be done with the human genome 16
  17. 17. Name ____________________________________ Date _________________ Per _____ 14-3 Section Review1. What is the Human Genome Project?2. Describe how gene therapy works.3. Name two common uses for DNA testing.4. Describe how molecular biologists identify genes in sequences of DNA.5. Critical Thinking Making Judgments Do you think it should be legal for people to use genetic engineering to affect their children’s characteristics? Give reasons for your answer. 17
  18. 18. Chapter 14 The Human GenomeReviewing ContentChoose the best answer.1. A normal human diploid zygote contains a full set of 23 chromosomes. 46 chromosomes. 44 chromosomes. XXY chromosomes.2. A chart that traces the inheritance of a trait in a family is called a(an) pedigree. karyotype. genome. autosome.3. Traits that are caused by the interaction of many genes are said to be polyploid. linked. polygenic. autosomal.4. An example of a trait that is determined by multiple alleles is Huntington’s disease. ABO blood groups. Down syndrome. hemophilia.5. Most sex-linked genes are found on the Y chromosome. O chromosome. YY chromosomes. X chromosome.6. Hemophilia is a genetic disorder that is sex-linked. sex-influenced. fairly common. more common in women than men.7. Which parental pair could produce females with colorblindness? homozygous normal-vision mother, father with colorblindness mother with colorblindness, normal-vision father heterozygous normal-vision mother, normal-vision father heterozygous normal-vision mother, father with colorblindness8. A common genetic disorder characterized by bent and twisted red blood cells is cystic fibrosis. hemophilia. sickle cell disease. muscular dystrophy. 189. Which of the following techniques takes advantage of repeated DNA sequences that do not code for proteins?
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