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Dragonfly Chapter 14 The Human Genome Section 14-1: Human Heredity Key Concepts: How is sex determined? How do small changes in DNA Cause genetic disorders? I. Human Chromosomes A. Karyotype: A picture of chromosomes taken during mitosis and cut out and arranged into homologous pairs. Diploid Cell: ________ Two sets of homologous chromosomes Human diploid cell has ____ 46 chromosomes arranged in ____ 23 pairs The 46 chromosomes contain 6 billion nucleotide pairs Mendelian genetics requires that organisms inherit a single copy of gene from each parent In humans, _______________ (reproductive cells the gametes of egg and sperm) contain a single copy of each gene (one set of genetic information). testes Gametes are formed in the __________ (sperm) and ovaries __________(egg) by meiosis. Each gamete contains 23 chromosomes (one set) or haploid number (N) of chromosomes. __________________ Fertilization ________________ requires the egg and the sperm to join and produce a ______________ (fertilized egg) zygote that contains 46 chromosomes (two sets) or diploid number _____________________ (2N). Humans have 46 total chromosomes 44 _____________ autosomes follow regular Mendelian genetics 2 _________________ sex chromosomes (X and Y) are sex-linked A. Pedigree Chart: A pedigree chart shows the _________________ within a family and can be relationship genetic inheritance problems useful to help with __________________________ within families. It is another __________________ way to predict the outcome of a particular cross and the genotype of _________ the family members. Figure 14-3 A Pedigree Section 14-1 Pedigree 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. 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. Human Traits Phenotypes are determined by genotype as well as ________________________________. environmentally influenced ________________________________ on gene Environmental influences expression are not inherited, but genes are. III. Human Genes The __________________: Complete set of genetic human genome information Composed of about 30,000 genes Blood Group Genes Human Blood comes in a variety of genetically determined blood groups There are many different types of blood groups but the ones associated with the ABO blood group and the Rh blood groups are best known. Rh blood groups is controlled by single gene with ________________. It is another antigen in blood, Two alleles first discovered in Rhesus monkeys. The arrangement of the alleles determines only _______ two positive possible types _____________ (+) contains the antigen, or ___________ (-) doesn’t contain the negative antigen. Positive is ______________ over negative. dominant Rh-positive is identified with two genotypes: Rh+/Rh+ or Rh+/RhRh-negative is identified with one genotype: Rh-/Rh- ABO Blood Groups: Discovered in 1900 by Karl Landsteiner. He realized that all blood is classified into four types: ____, A ____, O due to B ____, AB and _____ the presence of or absence of specific __________ antigens in the blood. o is Alleles IA and IB are __________________ and i codominant ________________ to both IA and IB recessive Antigens are ______________________ used by chemical markers the immune system. When an unrecognized antigen is present an immune response takes place and the cells ____________________________. clump or agglutinate Figure 14-4 Blood Groups Blood Type and Antigen Interactions Section 14-1 Phenotype (Blood Type Go to Section: Genotype Antigen on Red Blood Cell Safe Transfusions To From B. Recessive Alleles: Trait controlled by a recessive allele. This results in the disorder being present ___________________________. only if both alleles are recessive • Examples include: PKU (Phenylketonuria), Tay Sachs disease and Cystic Fibrosis, Albinism, and Galactosemia (See chart on page 345) C. Dominant Alleles: Traits controlled by a dominant allele. This results in the disorder being present when only one allele is present __________________________. • Examples include: Achondroplasia (dwarfism), Hypercholesterolemia, and Huntington’s Disease Section 14-1 Autosomal Disorders Autosomol Disorders caused by Recessive alleles Dominant alleles Codominant alleles include include include Huntington’s disease Sickle cell disease Galactosemia Albinism Cystic fibrosis Phenylketonuria Tay-Sachs disease Achondroplasia Hypercholesterolemia Huntington Disease: It is controlled by a _________________________. single dominant allele The gene is located on Chromosome #4. Genetic degenerative disease that shows no symptoms until a person is in their ____________________. It progresses with thirties or forties gradual degeneration of their nervous system leading to loss of muscle control and mental function until death occurs. Question? Would you want to know now if you could potentially get Huntington’s disease when you are older? Would you want to know if you could pass the gene on to your offspring before you have children? A. Codominant Alleles: controlled by _______________________________________. two alleles that share dominance Sickle Cell Anemia is such a disorder. (This will be discussed in detail later) IV. From Gene to Molecule The link between genetics ______________________ and phenotype is not easily determined but for several diseases we have been able to make the connection. Cystic fibrosis and Sickle cell disease For both _____________ ________________ single gene a small change in the DNA of a _____________ affects the ______________________, causing a structure of a protein serious genetic disorder. A. Cystic Fibrosis: (See figure 14-8 p. 347) Cystic Fibrosis a.k.a. “CF” is a common genetic disease. It is most common in people of Northern European decent. It is a _______________________ of a gene Recessive disease found on the # 7 chromosome and affects the______________________________ digestive and respiratory systems It is caused by the____________________ deletion of 3 bases in the middle of a sequence for a protein and causes the protein to be ______________ abnormal and doesn’t allow Chloride ions to transport across the membrane, as they should. This causes the cells in a person’s airways to be unable to transport chloride ions and become __________________. clogged with mucus Figure 14-8 The Cause of Cystic Fibrosis Section 14-1 Chromosome #7 CFTR gene 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. 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. B. Sickle Cell Anemia The patient’s blood cells were found to be irregularly shaped, ____________________, like a sickle and this is how the disease got its name. In normal red blood cells the ____________________ oxygen hemoglobin molecule carries ___________ and distributes it around the body. In sickle cell disease, the red blood cells are sickle–shaped, causing the blood hemoglobin to no longer carry oxygen as well and _____________________ disrupts the normal functioning of the bodies cells, tissues and organs This person is deprived of oxygen and the result is physical weakness, and damage to the brain, heart, spleen. It may be fatal. The cause: A _________________ in the DNA that single base codes for Hemoglobin polypeptides is changed. This substitutes Valine for glutamic acid. This change makes the hemoglobin less soluble in blood. This will cause the hemoglobin to come out of the blood and _______________. This crystallize crystallization causes the ________________ of sickle shape the blood cells and the medical consequences. The genetics: The allele for sickle cell (HS) is ___________ codominant with the allele for normal hemoglobin (HA). Heterozygotes (HS HA) are said to be ____ Sickle____ cell __________ carriers and have some effects of the disorder because they have both normal and sickle cell blood hemoglobin. DNA normal hemoglobin CAC GTG GAC TGA GGA CTC CTC Messenger RNA sequence GUG CAC CUG ACU CCU GAG GAG Normal hemoglobin amino acid sequence Val – His – Leu – Thr – Pro – Glu – Glu… 1 2 3 4 5 6 7 …146 DNA Sickle Cell Anemia CAC GTG GAC TGA GGA CAC CTC Messenger RNA sequence GUG CAC CUG ACU CCU GAG Val – His – Leu – Thr – Pro – – Glu… 1 2 3 4 5 6 7 …146 The distribution: Sickle Cell anemia is most prevalent in people of __________________. African descent 10% of African Americans and 40% of populations in Africa and Asia carry the gene for Sickle cell anemia. Why? The carriers for the disease have a ___________________, resistance to Malaria a dangerous disease caused by a blood parasite found in tropical areas of the world. Sickle Cell Anemia is a __________ mutation that has provided an ____________ in Malaria prone areas advantage and in these areas it is favored _______________________ by natural selection and therefore Sickle Cell Anemia persists. HS HA HS HS HS H S HA HA HS HA H A HA Section 14-2: Human Chromosomes Key concepts: Why are sex-linked disorders more common in males than in females? What is nondisjunction, and what problems does it cause? I. Human Genes and Chromosomes Human diploid cell contains ______________________ 6 billion base pairs of DNA. All neatly packed into the 46 chromosomes. __________________ of the DNA actually functions as Small part genes. Genes are located on the chromosomes and each gene occupies a ______________________ on a specific place chromosome. Genes may exist in ____________________ (alleles) several forms Each chromosome contains ______ one of the alleles for each of its genes Chromosome #21 and 22 are the ____________ smallest of the human autosomes. These were the first two chromosomes whose sequences had been determined. Both also contain genes for some genetic disorders like ________________________ Leukemia and Amyotrophic Lateral Sclerosis (ALS) ___________________________ We also discovered that there are many _________________________ segments of DNA non-coding, repeating Human chromosomes also have ________________ that can cross over just as we Linked genes saw in the fruit fly. II. Sex-linked Genes Sex Chromosomes 1. _______________________ are the ones that __________ in males and females differ 2. Chromosomes that are the ________ in male and same females = _______________ autosomes 3. In humans: females = ____ XY XX and Males = ____ 4. The Y chromosome is smaller than the X A. Sex Determination 1. Female _________ gametes carry an X chromosome 2. _________ gametes can carry either an X or Y Male (meiosis segregates the chromosomes; _______ 50% 50% of the sperm of the sperm carry X and ______ carry Y) 3. In humans, _____________________________ males determine the sex of an offspring X Y Female: XX X XX XY male: XY X XX XY In some animals such as birds, butterflies, and some fish, the female determines the sex differing chromosomes. because she has the __________ Sex-linked Genes 1. In addition to determining the sex of an individual, the sex chromosomes carry genes that ____________________ affect other traits. Sex-linked Genetic Disorders May be on the X or Y chromosome, but usually on the X because the Y has very few genes. males Most often expressed in ____________because they only have one X chromosome and thus all the alleles are expressed even if they are recessive. Colorblindness is a recessive disorder in which people can’t distinguish between certain colors. Red-green ____________________ colorblindness is most common. XC and Xc are ________________ for normal and the alleles colorblind vision. XC XC and XC Xc are both normal vision females. carrier for colorblindness and can XC Xc is a _______________________ pass the gene on to her sons. Xc Xc is a colorblind female. XC Y is a normal male and Xc Y is a colorblind male. http://www.toledo-bend.com/colorblind/Ishihara.html Figure 14-13 Colorblindness 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 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: Hemophilia is a __________________________ recessive sex-linked disorder in which one is unable to clot their blood. Also known as “bleeders disease”. Hemophilia is caused by a defect in a gene and the protein for normal blood clotting is missing. Figure 21.12 Page 394 Slide 16 Royal Family and Hemophilia I II III Albert Victoria IV V VI Figure 21.13 Page 394 Slide 18 Muscular Dystrophy is another sex-linked recessive disease. Here the affected individual inherits a degenerative __________disorder. muscle The gene that codes for a _____________ muscle protein is defective. They rarely live past early adulthood. Treatments are being explored that ___________ replace the defective gene. III. X-Chromosomes Inactivation Males survive with only one X chromosome so, what do females do with 2? They ___________; shut one off it becomes inactive. This creates a dense region in the nucleus known as a ______________. Barr body This is seen in coat color in cats. The cells will randomly shut off the coat color allele in one X chromosome and turn them off in the other X chromosome in other cells and this leads to some areas that are spotted orange and some spotted black, creating a tricolor cat, ________. This calico only happens in __________ females because males only have one X chromosome. IV. Chromosomal Disorders Whole/sets of chromosome mutations 1. _______________ Nondisjunction = failure of homologous chromosomes to separate normally during meiosis This results in a disorder of __________________ chromosome number 2. Examples of disorders include Down’s Syndrome, Klinefelter’s, and Turner’s Syndrome Section 14-2 Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Go to Section: Meiosis II Nondisjunction Section 14-2 Homologous chromosomes fail to separate Meiosis I: Nondisjunction Go to Section: Meiosis II Nondisjunction Section 14-2 Homologous chromosomes fail to separate Meiosis I: Nondisjunction Go to Section: Meiosis II Nondisjunction n+1 n+1 n-1 n-1 chromosome alignments at metaphase I nondisjunction at anaphase I alignments at metaphase II anaphase II gametes Figure 21.19 Page 398 Slide 23 2. Examples of disorders include Down’s Syndrome, Klinefelter’s, and Turner’s Syndrome Nondisjunction disorders: Disorders in which the failure of _____________________ chromosome separation during one of the stages of meiosis causes a gamete to have _______________________________. too few or too many chromosomes Nondisjunction can occur in ___________________________. autosomes or sex chromosomes Down’s Syndrome: Down’s syndrome is an example of ____________________________, nondisjunction of an autosome specifically chromosome 21. In Down’s syndrome there is an ___________ extra copy of chromosome 21 (trisomy 21). Doing a _____________ karyotype (display of all the chromosomes in a cell nucleus) and looking at the chromosomes under a microscope detect the extra chromosome. Characteristics of Down’s syndrome include _________________, mental retardation physically challenged, facial irregularities, and often heart defects. incidence per 1,000 births Incidence of Down’s Syndrome and mother’s age 20 15 10 5 0 20 25 30 35 40 45 mother's age Fig. 21.20a,b Page 399 Slide 24 Turners Syndrome: Nondisjunction of the sex chromosomes in which a chromosome is missing. 45 XO They have the chromosome makeup of _________ where “O” represents the missing chromosome. This individual is female in appearance but does not develop the female sex organs during puberty and is sterile. ________. Klinefelter’s Syndrome: Nondisjunction of the sex extra X chromosome chromosomes in which an _____________________ is present. 47XXY They have the chromosome makeup of ________. male They are ___________ in appearance and are also sterile. May also be 48 XXXY or 49 XXXXY No nondisjunctions of the sex chromosomes have ever X chromosome produced and survived without an ______________. This is because the X chromosome carries many genes essential for life. •XXY condition •Results mainly from nondisjunction in mother (67%) •Phenotype is tall males –Sterile or nearly so –Feminized traits (sparse facial hair, somewhat enlarged breasts) –Treated with testosterone injections Nondisjunction of Sex Chromosomes XX x Y XX x X O x Y x X gamete XX XXY (Klinefelter syndrome) or nondisjunction XXX (“metafemale”) XX gamete O YO (not viable) or O meiosis and possibilities gamete formation at fertilization XO (Turner syndrome) genotype (phenotype) Figure 21.21 Page 399 Slide 25 The impact of the sex chromosome nondisjunction has led us to understand the importance of the _____________________ Y chromosome in determination of sex of an individual. This has recently been determined to be true because the Y chromosome has been found to have a gene that turns on ______________________ male sexual development in the embryo even if many X chromosomes are present.