College Prep Biology Chapter 14 notes

1. College Prep BiologyChapter 14 notes The Human Genome

2. Chapter 14 Section 1: human heredity • A karyotype is a picture of chromosomes arranged in pairs • Human body cells contain 46 chromosomes; a sperm cell contains 23 chromosomes and an egg cell contains 23 chromosomes • Once the sperm cell fertilizes the egg cell, the fertilized egg will contain 46 chromosomes • Sex chromosomes determine an individual’s sex (females have the genotype of xx and males have a genotype of xy)

3. Chromosomes continued • Autosomes are the other 44 chromosomes in the human cell • Females would be represented as 46xx and males would be 46xy • The x chromosome is longer than the y chromosome • Human chromosomes contain both DNA and protein. Each chromosome contains a single, double stranded DNA molecule.

4. Human traits • Human genes are inherited according to the same principles that Gregor Mendel discovered working with garden peas. • A pedigree is a chart that shows the relationships within a family. It helps to show traits that are inherited. It also shows how the trait is passed from one generation to the next

5. Human traits are impossible to associate with single genes because: • Many traits are polygenic (controlled by many genes) • Personal traits are controlled by genetics AND the environment • *LETS TRY THE PROBLEM SOLVING “USING A PEDIGREE” ON P 343 OF YOUR BOOK*

6. HUMAN GENES • THE HUMAN GENOME IS A COMPLETE SET OF GENETIC INFORMATION • THE DNA SEQUENCE OF THE HUMAN GENOME WAS COMPLETED IN THE YEAR 2000. • IT ALLOWS SCIENTISTS TO IDENTIFY GENES THAT DIRECTLY CONTROL A SINGLE HUMAN TRAIT

7. BLOOD GROUP GENES • There are ABO and Rh blood groups • Rh is determined by a single gene with 2 alleles: a positive and a negative • Rh+ is dominant=Rh+/Rh+ or Rh+/Rh • Rh-/Rh- = recessive

8. Abo blood group • ABO blood group has three alleles: i,IA, and IB • IA and IB are co-dominant: they produce antigens that are recognized by the immune system • IA/IB=blood type AB • i=recessive • IAIA or IAi= A antigen only; blood type A • IBIB or IBi= B antigen only; blood type B • ii= no antigens; blood type O • Example: AB negative blood means there is IA allele, IB allele and Rh- allele

9. Recessive alleles • In most cases, the presence of a normal, functioning gene is revealed only when an abnormal or nonfunctioning allele affects the phenotype

10. Phenylketonuria (pku) • People with this disease lack the enzyme needed to break down the amino acid phenylalanine • Phenylalanine is found in milk & other foods • Phenylalanine builds up in tissues of the child and causes severe mental retardation • Newborns can be tested for PKU & put on a diet restricting phenylalanine • PKU is caused by a recessive allele on chromosome 12

11. Taysachs disease • This disease causes damage & breakdown to the nervous system. Death occurs in the first few years of life. • It is common in Jewish families of European ancestry • It is caused by an autosomal recessive allele • There is no cure; testing is available to check for the probability of a child inheriting the disease

12. Dominant alleles • Remember, the effects of a dominant allele are expressed even when the recessive allele is present • Dwarfism aka achondroplasia is an example of a disease caused by a dominant allele • Huntington’s disease: nervous system disorder that causes a progressive loss of muscle control and mental function until death occurs

13. Co-dominant alleles • Sickle cell anemia: 1 of every 500 African Americans are affected by this disease

14. From gene to molecule • In both cystic fibrosis and sickle cell disease, a small change in the DNA of a single gene affects the structure of a protein, causing a serious genetic disorder

15. Cystic fibrosis • Most common among people whose ancestors came from Northern Europe • It is caused by a recessive allele on chromosome 7 • It causes serious digestive problems • You produce a thick, heavy mucus that clogs lungs and breathing passageways • Only half of all children born with CF survive into their 20’s • Cf occurs when 3 bases are deleted in the middle of a sequence for a proteinthe protein folds improperly and the cells do not transport the protein to the cell membrane so it is destroyed

16. Sickle cell disease • Common in African Americans • Bent and twisted shape of red blood cells that are more rigid than normal • The sickled cells get stuck in capillaries because of their shapeblood stops flowing which damages cells and tissues • Physical weakness, damage to the brain, heart and spleen are symptoms associated with the disease

17. Sickle cell disease cont. • Abnormal hemoglobin is less soluble than normal hemoglobin: decrease in blood oxygen levels causes hemoglobin molecule to stick together forming “sickle cells” • A benefit is that low oxygen levels cause some red blood cells to become sickle shaped and when the body gets rid of sickled cells, it gets rid of the parasite that causes malaria as well

18. DOMINANT OR RECESSIVE? • What makes an allele dominant, recessive, or co-dominant? • The nature of a gene’s protein product and its role in the cell • STUDY FOR YOUR QUIZ! IT WILL BE THE DAY AFTER TOMORROW 

19. 14-2 HUMAN CHROMOSOMES • A HUMAN DIPLOID CELL CONTAINS MORE THAN 6 BILLION NUCLEOTIDE PAIRS OF DNA • IF A COMPLETE HUMAN DNA SEQUENCE WERE TO BE WRITTEN IN THE SAME SIZE FONT AS OUR TEXTBOOK, THE BOOK WOULD BE MORE THAN 4 MILLION PAGES LONG!!! • ALL OF THIS INFORMATION IS NEATLY PACKED INTO 46 CHROMOSOMES (THINK OF EACH CHROMOSOME AS A LIBRARY CONTAINING THOUSANDS OF BOOKS)

20. HUMAN GENES AND CHROMOSOMES • CHROMOSOMES 21 AND 22 ARE THE SMALLEST HUMAN CHROMOSOMES, THEREFORE THEIR SEQUENCES WERE DETERMINED FIRST • CHROMOSOME 22 CONTAINS @ 43 MILLION DNA BASES AND 545 GENES. IT IS A VERY IMPORTANT HEALTH CHROMOSOME GENETIC DISORDERS INCLUDE LEUKEMIA, NEUROFIBROMATOSIS IF REARRANGEMENTS OCCUR WITHIN DNA

21. HUMAN GENES CONTINUED • CHROMOSOME 21 CONTAINS @ 32 MILLION DNA BASES AND 225 GENES. LOU GEHRIG’S DISEASE (ALS) OCCURS IS CHROMOSOME 21 IS AFFECTED • LET’S TAKE A LOOK AT THE HUMAN KARYOTYPE ON P 341 OF YOUR TEXTBOOK: • WHICH CHROMOSOMES ARE THE SMALLEST? • WHICH CHROMOSOMES ARE THE LARGEST? • CONSIDERING CHROMOSOME SIZE, HOW MANY BASES MIGHT CHROMOSOME 1 HAVE IF CHROMOSOME 22 HAS ABOUT 43 MILLION BASES? • IS IT LIKELY THAT SCIENTISTS WILL DISCOVER THE SEQUENCES ON ALL CHROMOSOMES?

22. SEX LINKED GENES • GENES FOUND ON THEY X CHROMOSOME; THERE IS A SPECIAL PATTERN OF INHERITANCE FOR THESE GENES • MORE THAN 100 SEX LINKED GENETIC DISORDERS HAVE BEEN MAPPED TO THE X CHROMOSOME; THE Y CHROMOSOME IS MUCH SMALLER AND CONTAINS ONLY A FEW GENES

23. COLORBLINDNESS • 3 HUMAN GENES ASSOCIATED WITH COLOR VISION ARE LOCATED ON THE X CHROMOSOME • IN MALES, A DEFECTIVE VERSION OF ANY OF THE 3 GENES PRODUCES COLORBLINDNESS  • RED-GREEN COLORBLINDNESS IS THE MOST COMMON (1:10 MALES IN THE U.S.) • IN FEMALES, THE DISORDER IS RARE (1:100) • SINCE MALES HAVE ONLY 1 X CHROMOSOME, THE X LINKED ALLELES ARE EXPRESSED, EVEN IF THEY ARE RECESSIVE. IN ORDER FOR A RECESSIVE ALLELE TO BE EXPRESSED IN FEMALES, THERE MUST BE 2 COPIES (ONE ON EACH CHROMOSOME)

24. HEMOPHILIA • THE PROTEIN NECESSARY FOR NORMAL BLOOD CLOTTING IS MISSING • PEOPLE CAN BLEED TO DEATH FROM MINOR CUTS OR SUFFER INTERNAL BLEEDING FROM BUMPS/BRUISES • IT CAN BE TREATED BY INJECTIONS OF NORMAL CLOTTING PROTEINS • RECESSIVE ALLELE IN EITHER OF THE 2 BLOOD CLOTTING GENES CAUSES HEMOPHILIA

25. DUCHENNE MUSCULAR DYSTROPHY • RESULTS IN PROGRESSIVE WEAKENING AND LOSS OF SKELETAL MUSCLE • PEOPLE RARELY LIVE PAST EARLY ADULTHOOD • 1:3000 MALES IN THE U.S. ARE AFFECTED • IT IS CAUSED BY A DEFECTIVE VERSION OF THE GENE THAT CODES FOR A MUSCLE PROTEIN

26. X CHROMOSOME INACTIVATION • IN FEMALE CELLS, ONE X CHROMOSOME IS RANDOMLY SWITCHED OFF. IT FORMS A DENSE REGION IN THE NUCLEUS KNOWN AS A BARR BODY. BARR BODIES ARE NOT FOUND IN MALES BECAUSE THEIR SINGLE X CHROMOSOME IS STILL ACTIVE • EXAMPLE: IN CATS, ONE X CHROMOSOME MAY HAVE AN ALLELE FOR ORANGE SPOTS AND THE OTHER, BLACK SPOTS. IN CELLS IN DIFFERENT PARTS OF THE BODY, ONE X CHROMOSOME IS SWITCHED OFF. AS A RESULT, THE CAT’S FUR WILL HAVE A MIXTURE OF ORANGE AND BLACK SPOTS. MALE CATS ONLY HAVE 1 X CHROMOSOME THEREFORE THEY CAN ONLY HAVE SPOTS OF ONE COLOR 

27. CHROMOSOMAL DISORDERS • THE MOST COMMON ERROR IN MEIOSIS OCCURS WHEN HOMOLOGOUS CHROMOSOMES FAIL TO SEPARATE = NONDISJUNCTION • IF NONDISJUNCTION OCCURS, ABNORMAL NUMBERS OF CHROMOSOMES MAY FIND THEIR WAY INTO GAMETES AND A DISORDER OF CHROMOSOME NUMBER MAY RESULT.

28. DOWN SYNDROME • IF 2 COPIES OF AN AUTOSOMAL CHROMOSOME FAIL TO SEPARATE, AN INDIVIDUAL MAY BE BORN WITH 3 COPIES OF A CHROMOSOME = TRISOMY • TRISOMY-21 (DOWN SYNDROME) OCCURS IN 1:800 IN U.S.; IT CAUSES MILD TO SEVERE MENTAL RETARDATION AND AN INCREASED SUSCEPTIBILITY TO DISEASES AND BIRTH DEFECTS

29. SEX CHROMOSOME DISORDERS • TURNERS SYNDROME: NONDISJUNCTION OF A FEMALE • XO GENOTYPE • STERILE BECAUSE THE SEX ORGANS DON’T DEVELOP • KLINEFELTERS SYNDROME: NONDISJUNCTION OF A MALE • XXY GENOTYPE • EXTRA X CHROMOSOME INTERFERES WITH MEIOSIS AND USUALLY PREVENTS THE INDIVIDUAL FROM REPRODUCING

30. SEX CHROMOSOMES CONTINUED • THE Y CHROMOSOME CONTAINS A SEX DETERMINING REGION NECESSARY TO PRODUCE MALE SEXUAL DEVELOPMENT. IF THIS REGION ON THE Y CHROMOSOME IS ABSENT, THE EMBRYO DEVELOPS AS A FEMALE. • STUDY FOR YOUR QUIZ!!!!!

31. 14-3: human molecular genetics • Biologists search the human genome using DNA sequences • Testing for alleles: since the alleles for genetic disorders have slightly different DNA sequences from their normal counterparts, genetic tests can spot these differences. • We can use labeled DNA probes, look at changes in restriction enzyme cutting sites, and look at differences in lengths of normal and abnormal alleles

32. Testing for alleles continued • DNA testing can pinpoint the exact genetic bases of a disorder • This makes it possible to develop more effective therapy and treatment for individuals affected by genetic disease

33. DNA Fingerprinting • DNA fingerprinting is an analysis of sections of DNA that have little or no known function, but vary widely from one individual to another in order to aid in identification • A small sample of human DNA is cut with a restriction enzyme • The resulting fragments are separated by size using gel electrophoresis 3. DNA probes detect variable regions and reveal DNA bands of various sizes

34. Dna fingerprinting continued 4. Each pattern of bands is distinguished from everyone else in the world (except identical twins) 5. DNA samples can be obtained from blood, sperm, and hair strands **This process has been used in the U.S. since the late 1980’s and helps to convict criminals as well as overturn wrong convictions

35. Human genome project • DNA sequence of E. coli bacteria was determined in 1996: it contains 4,639,221 base pairs! • The Human Genome Project is an attempt to sequence all of the DNA in human beings. It was completed in 2000. • Biotechnology companies are rushing to find genetic information that may be useful in developing new drugs and treatments for diseases. • Genome research is posted on the Internet on a daily basis

36. 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 allows the body to make the correct protein or enzyme it needs. • Example: In 1999, a young girl was CURED of an inherited immune disorder when cells from her bone marrow were removed, modified, and then placed back in her body

37. Practicing gene therapy • A virus is modified so it cannot cause disease • A DNA fragment containing a replacement gene is spliced to viral DNA • The patient is infected with modified virus particles • The virus carries the gene into cells to correct genetic defects *Gene therapy is still a high-risk procedure though 

38. Ethical issues in human genetics • The goal of biology is to gain a better understanding of the nature of life. The more biologists understqnd life, the more they will be able to manipulate it. • Should we manipulate cells to cure disease? • Should we engineer taller people or change their eye color? • Should we change hair texture, sex, or blood groups? • STUDY FOR YOUR TEST ON CHAPTER 14!