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Chapter 14 The Human Genome 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. Let us review what we have previously learned A Diploid Cell has ________ two sets of homologous chromosomes. A human diploid cell has ____ 46 chromosomes arranged in ____ 23 pairs. Mendelian genetics requires that organisms inherit ____________of a gene from each parent. a single copy In humans, ___________ the gametes (reproductive cells of egg and sperm) contain a single copy of each gene (one set of genetic information). Gametes are formed in the ______ testes (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 ______ zygote (fertilized egg) that contains diploid number (2N). 46 chromosomes (two sets) or _____________ autosomes Humans have 46 total chromosomes: 44 _________ (body) that follow regular Mendelian genetics, and 2 ________________ sex chromosomes (X and Y). A. A pedigree chart shows the __________ relationship within a family and can be useful to help with genetic __________ inheritance problems within families. B. It is another way to _______ predict an 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. Video Notes Worksheet: What are Pedigree Charts? Video Notes Worksheet: Pedigree Analyses Guided Practice Video Notes Worksheet: Pedigree Summary Human Genes The ______________: human genome Complete set of genetic information that is composed of about 30,000 genes. Human Traits Phenotypes are determined by __________as well genotypes as ______________ environmentally influenced. _____________ Environmental influences on gene expression are not ________, inherited but genes are. A trait controlled by a recessive allele results in a disorder being present both alleles are present. only if _____________ • Examples include: PKU (Phenylketonuria), Tay Sachs, Cystic Fibrosis, Albinism, and Galactosemia. A trait controlled by a dominant allele results in the disorder being present one allele is present. when only ________ • Examples include: Achondroplasia (dwarfism), Hypercholesterolemia, and Huntington’s Disease Autosomal Disorders 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 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. IV. From Gene to Molecule genetics and phenotype The link between ______________________ is not easily determined but for several diseases we have been able to make the connection. For both ______________ Cystic fibrosis and __________________ Sickle cell disease single gene a small change in the DNA of a _____________ structure of a protein causing a affects the ______________________, serious genetic disorder. Codominant Alleles: controlled by _____________________________. two alleles that share dominance • Sickle Cell Anemia is an example. 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 hemoglobin oxygen ___________carries _________and distributes it around the body. In sickle cell disease, the red blood cells are sickle–shaped, causing hemoglobin to no longer carry oxygen as well and disrupts the normal functioning of cells. Cystic Fibrosis or “CF” is a common genetic disease. It is most common in people of Northern European decent. Recessive disease a gene found It is a __________________of on the # 7 chromosome and affects digestive and respiratory systems the__________________________________. Figure 14-8 The Cause of Cystic Fibrosis Chromosome Section 14-1 #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. 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 GUG GAG Val – His – Leu – Thr – Pro – VAL – 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 _________ advantage in Malaria prone areas. In these areas it is _________________________ favored by natural selection and therefore Sickle Cell Anemia persists in many heterozygous individuals since the homozygous recessive condition is lethal. HS HA HS HS HS HS HA HA HS H A HA 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? A. Sex Determination 1. Female _________ gametescarry an X chromosome 2. _________ gametes can carry either an X or Y (meiosis segregates Male the chromosomes; _______ of the sperm carry X and ______ of the sperm carry Y) 50% 3. In humans, _____________________________ of an 50% offspring Female: XX male: XY males determine the sex X X XX Y XY X XX XY 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. ____________________ colorblindness is most Red-green common. the alleles for normal and XC and Xc are ___________ 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 Muscular Dystrophy is another sex-linked recessive disease. Here the affected individual inherits a degenerative muscle __________disorder. muscle protein is The gene that codes for a _____________ defective. They rarely live past early adulthood. replace Treatments are being explored that ___________ the defective gene. 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 Nondisjunction 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 separationduring 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 of Down’s Syndrome and mother’s age 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 The impact of the sex chromosome nondisjunction has led us to understand the Y chromosome in importance of the ____________ determination of the 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 characteristics in the embryo, even if there are many X chromosomes present.