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Karyotype Autosome centromere Sex Go to Section: Chromosomes Go to Section: Figure 14-3 A Pedigree Section 14-1 A circle represents a female. A horizontal line connecting a male and female represents a marriage. A half-shaded circle or square indicates that a person is a carrier of the trait. A completely shaded circle or square indicates that a person expresses the trait. Go to Section: A square represents a male. A vertical line and a bracket connect the parents to their children. A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait. Go to Section: Genotype SS Ss Phenotype Normal Hemoglobin Sickle Cell Trait ss Sickle Cell Anemia Go to Section: Comments Normal Blood Sickles under low O2 Can survive malaria Usually dies Protein becomes less soluble and sticky Go to Section: For example, sickle-cell disease is caused by a mutation of a single base pair substitution in the gene that codes for one of the polypeptides of hemoglobin. – A change in a single nucleotide from T to A in the DNA template leads to an abnormal protein. Go to Section: Fig. 17.23 Figure 14-8 The Cause of Cystic Fibrosis Section 14-1 Chromosome #7 CFTR gene deletion The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein. Protein misfolds and makes the protein channel nonfunctional Go to Section: Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane. The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus. Go to Section: Go to Section: Go to Section: Tay Sachs Lipid builds up in brain, Mental retardation. Blindness. Go to Section: Achondroplasia A type of dwarfism caused by a dominant allele Go to Section: Concept Map Section 14-1 Autosomol Disorders caused by Recessive alleles Dominant alleles Codominant alleles include include include Huntington’s disease Sickle cell disease Galactosemia Albinism Cystic fibrosis Go to Section: Phenylketonuria Tay-Sachs disease Achondroplasia Hypercholesterolemia Figure 14-4 Blood Groups Section 14-1 Phenotype (Blood Type Go to Section: Genotype Antigen on Red Blood Cell Safe Transfusions To From Interest Grabber Section 14-2 Gender Benders You may remember that in humans, the sperm cells may carry an X chromosome or a Y chromosome, while egg cells have only X chromosomes. Sometimes, errors during meiosis in one of the parents produce offspring with an abnormal number of sex chromosomes. Go to Section: Interest Grabber continued Section 14-2 1. On a sheet of paper, construct a Punnett square for the following cross: XX x XY. Fill in the Punnett square. What does the Punnett square represent? According to the Punnett square, what percentage of the offspring from this genetic cross will be males? What percentage will be females? 2. On a sheet of paper, construct a Punnett square for the following cross: XXX x XY. Fill in the Punnett square. How is this Punnett square different from the first one you constructed? What might have caused this difference? 3. How do the offspring in the two Punnett squares differ? Go to Section: Section Outline Section 14-2 14–2 Human Chromosomes A. Human Genes and Chromosomes B. Sex-Linked Genes 1. Colorblindness 2. Hemophilia 3. Duchenne Muscular Dystrophy C. X-Chromosome Inactivation D. Chromosomal Disorders 1. Down Syndrome 2. Sex Chromosome Disorders Go to Section: Males determine the sex half the sperm have an X and the other half has a Y Sex Linked Gene= a gene on the X sex chromosome Genotype Phenotype XRXR Red ♀ XRXr Red ♀ XrXr XRY Xr Y Go to Section: XR Y Xr XRXr XrY Xr XRXr XrY White ♀ Red ♂ White ♂ F1 Genotypic ratio= 2:2 Go to Section: Go to Section: 1. What are the possible genotypes for eye color of a female fruit fly? Of a male? Female; XRXR, XRXr, or XrXr; male: XRY or XrY Go to Section: 2. Construct a cross that could produce a white-eyed female fruit fly. Students should show a cross between a whiteeyed male (XrY) and a heterozygous female (XRXr) or a homozygous recessive female (XrXr). Homozygous recessive female offspring (XrXr) will have white eyes. Go to Section: Males determine the sex half the sperm have an X and the other half has a Y Sex Linked Gene= a gene on the X sex chromosome Genotype Phenotype XRXR Red ♀ XRXr Red ♀ XrXr XRY Xr Y Go to Section: Xr Y XR XRXr XRY Xr Xr Xr XrY White ♀ Red ♂ White ♂ F2 Genotypic ratio= 1:1:1:1 Colorblindness is a sex-linked recessive trait . Make a Genotype/Phenotype chart for colorblindness. Go to Section: Carrier – a normal female with a sex linked recessive trait Go to Section: Genotype Phenotype XCXC Normal ♀ XCXc Normal ♀ (carrier) XcXc Color Blind ♀ XCY Normal ♂ XcY Color Blind ♂ Genotype H H X X H h X X h h X X H XY h XY Phenotype Normal ♀ Normal ♀(Carrier) Hemophiliac ♀ Normal ♂ Hemophiliac ♂ Carrier= A normal female with a sex linked recessive gene. Go to Section: Genotype Phenotype XRXR Normal ♀ XRXr Normal ♀ XrXr Color Blind ♀ Normal ♂ XRY XrY Go to Section: Color Blind ♂ Figure 15.11 X Two cell populations in adult inactivation andcat: the tortoiseshell Active X Early embryo: Orange fur X chromosomes Cell division Inactive X and X chromosome Inactive X inactivation Black fur Allele for orange fur Allele for black fur Go to Section: Active X cat Genotype XBXB XBXb b b XX B X Y XbY Sex Linked Gene -A Gene on the X Sex Chromosome Go to Section: Phenotype Yellow Female Tortoise Shell Female Black Female Yellow Male Black Male Figure 14-13 Colorblindness Section 14-2 Father (normal vision) Colorblind Normal vision Male Female Daughter (normal vision) Son (normal vision) Daughter (carrier) Son (colorblind) Mother (carrier) Go to Section: Figure 14-13 Colorblindness Section 14-2 Father (normal vision) Colorblind Normal vision Male Female Daughter (normal vision) Son (normal vision) Daughter (carrier) Son (colorblind) Mother (carrier) Go to Section: Go to Section: Go to Section: Go to Section: Go to Section: Go to Section: 1. Describe how nondisjunction in meiosis I and in meiosis II differ. Meiosis I: homologous chromosomes fail to separate; meiosis II: sister chromatids fail to separate. Go to Section: 2. How is it possible for nondisjunction to occur and for some normal gametes to be produced? If nondisjunction occurs in meiosis II, two of the four resulting gametes will be normal haploid. Go to Section: Go to Section: Go to Section: Trisomy 21 Down’s Syndrome Trisomy 18 Trisomy 15 Edward’s Syndrome Go to Section: XY XY O Aneuploidy X Go to Section: Nondisjunction of the sex chromosomes can result in XXY and XO Go to Section: Go to XXY-Klinefelter’s Syndrome Section: XO=Turner’s Syndrome Go to Section: Interest Grabber Section 14-3 Bioethics and You As you become more aware of scientific advances in genetics, you might realize that with the ability to manipulate genes, there comes responsibility. This ability provides an opportunity to improve the lives of many people. But there is also a potential for errors or intentional misuse of the technology. Go to Section: Interest Grabber continued Section 14-3 Working with a partner, answer the following questions. 1. In what type of situation do you think genetic engineering—changing the genes of organisms—is warranted? Explain your reasoning about your position. If you do not think that genetic engineering is ever warranted, explain your reasons for your position. 2. In what type of situation do you think genetic engineering might be misused? Suggest limits that might be placed on the manipulation of genes to avoid its misuse. Go to Section: Section Outline Section 14-3 14–3 Human Molecular Genetics A. Human DNA Analysis 1. Testing for Alleles 2. DNA Fingerprinting B. The Human Genome Project 1. Rapid Sequencing 2. Searching for Genes 3. A Breakthrough for Everyone C. Gene Therapy D. Ethical Issues in Human Genetics Go to Section: Go to Section: Restriction enzymes can only fit the DNA at a specific base sequence EX: CTTAAG Animation Animation Go to Section: Go to Section: Go to Section: Figure 13-6 Gel Electrophoresis Section 13-2 Power source DNA plus restriction enzyme Longer fragments Shorter fragments Mixture of DNA fragments Gel http://learn.genetics.utah.edu/units/biotech/gel/ Gel Electrophoresis simulation Go to Section: Go to Section: P 373 Differences in DNA sequences on homologous chromosomes result in different restriction fragment length patterns RFLP - these may be sorted by length using gel electrophoresis Go to Section: Presence of black bars indicates the target gene is in the sample Go to Section: Using dyes or radioactive DNA probes can determine the presence of particular sections DNA in a sample – DNA fingerprint Go to Section: Different people have different DNA -DNA when cut by enzymes will leave different size fragments -which will separate into different electrophoresis patterns -a DNA fingerprint If there is only a small sample of DNA available- more copies can be made by PCR -polymerase chain reaction (p371) Link to DNA Fingerprint Lab Go to Section: Figure 14-18 DNA Fingerprinting Section 14-3 Restriction enzyme Chromosomes contain large amounts of DNA called repeats that do not code for proteins. This DNA varies from person to person. Here, one sample has 12 repeats between genes A and B, while the second sample has 9 repeats. Go to Section: Restriction enzymes are used to cut the DNA into fragments containing genes and repeats. Note that the repeat fragments from these two samples are of different lengths. The DNA fragments are separated according to size using gel electrophoresis. The fragments containing repeats are then labeled using radioactive probes. This produces a series of bands—the DNA fingerprint. Figure 13-7 DNA Sequencing Section 13-2 Go to Section: DNA sequencing notebook Go to Section: Single stranded cDNA is made from a target cell’s active mRNA and tagged with a fluorescent dye DNA Microarray Identifies Active Genes A DNA Chip is a microarray of many spots where single stranded DNA is attached – each strand representing a different gene. If a gene is active the dye labeled cDNA will attach and cause that spot to light up when a laser strikes it. This tells you which genes are active. Go to Section: Figure 14-21 Gene Therapy Section 14-3 Bone marrow cell Normal hemoglobin gene Nucleus Chromosomes Genetically engineered virus Go to Section: Bone marrow Go to Section: Go to Section: Videos Click a hyperlink to choose a video. Human Sex Determination Nondisjunction Point Mutation Video 1 Human Sex Determination Click the image to play the video segment. Video 2 Nondisjunction Click the image to play the video segment. Video 3 Point Mutations Click the image to play the video segment. Go Online Links from the authors on DNA samples Career links on geneticists More information on the Human Genome Project Interactive test For links on pedigrees, go to www.SciLinks.org and enter the Web Code as follows: cbn-4141. Interest Grabber Answers 1. This pedigree shows the inheritance of attached ear lobes. Which parent has attached ear lobes? The father 2. How many children do the parents have? Which child has attached ear lobes? Three; the daughter has attached ear lobes. 3. Which child is married? Does this child’s spouse have attached ear lobes? Do any of this child’s children have attached ear lobes? The second son; no; yes, the daughter Interest Grabber Answers 1. On a sheet of paper, construct a Punnett square for the following cross: XX x XY. Fill in the Punnett square. What does the Punnett square represent? According to the Punnett square, what percentage of the offspring from this genetic cross will be males? What percentage will be females? One half of the offspring will be males; the other half, females. 2. On a sheet of paper, construct a Punnett square for the following cross: XXX x XY. Fill in the Punnett square. How is this Punnett square different from the first one you constructed? What might have caused this difference? One of the gametes has two X chromosomes instead of just one. This might have resulted from a mistake in meiosis: Instead of separating, the pair of X chromosomes stayed together. 3. How do the offspring in the two Punnett squares differ? Instead of two XX and two XY offspring, there are one XX and one XY (which are normal), plus one XXX and one XXY (which are abnormal). Interest Grabber Answers 1. In what type of situation do you think genetic engineering—changing the genes of organisms—is warranted? Explain your reasoning about your position. If you do not think that genetic engineering is ever warranted, explain your reasons for your position. Students’ answers likely will include medicinal uses of genetic engineering, such as gene therapy for genetic diseases and production of needed substances such as insulin. Some students may object to all genetic manipulations. 2. In what type of situation do you think genetic engineering might be misused? Suggest limits that might be placed on the manipulation of genes to avoid its misuse. Students’ answers may include the “designing” of human babies with desirable traits and the cloning of humans. Some students may object to genetically altered foods. This slide is intentionally blank.