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Human Genome Chapter 14 Sections 1-3 14-1 Human Heredity • Karyotype – a picture of chromosomes arranged in homologous pairs. Humans have 46 chromosomes: 23 from the male 23 from the female 44 autosomes 2 sex chromosomes • Autosomal Chromosome – (Autosomes) the 44 chromosomes in a Karyotype that are not sex chromosomes. • Sex Chromosomes- determine an individual’s sex Females have 2 copies of a large X chromosome. Males have 1 X & 1 small Y chromosome. Male vs. Female • Males and Females are born in a roughly 50:50 ratio because of the way in which sex chromosomes segregate during meiosis. • Females produce human egg cells that carry a single X chromosome. • The female inherits 1 copy of every gene located on each X chromosome. • Half of all sperm cells carry an X chromosome and half carry a Y chromosome. (50% XX, 50%XY) Mendelian Genetics • Biologists must identify an inherited trait controlled by a single gene. • Establish that the trait is inherited and not a result of environmental influence. • Study how the trait is passed from one generation to the next. • Use a Pedigree Chart. Pedigree Chart • Pedigree – chart that shows the relationships with in a family. Ex. Pg. 342, fig. 14-3 • The inheritance of a certain trait in a family can be traces using a pedigree. • It shows how a trait can be passed from one generation to the next. • It determined whether an allele is dominant or recessive. • The circle represents a Female and the square represents a Male. Figure 14-3 A 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. Genetic Traits • Polygenic – controlled by many genes. None are dominant. Ex. Shape of eyes and ears, height, skin color, and eye color. • Many traits are strongly influenced by environmental factors like nutrition and exercise. Ex. Height is largely determined by genetic factors, but nutritional improvement can increase the average height. Human Genome • The first human genes to be identified were those that control blood type. • Red blood cells carry 2 different antigens called A and B. • Antigen – molecules that are recognized by the immune system. Ex. ABO blood groups and Rh blood groups. • ABO – single gene w/ multiple alleles (3) Ex. I ,I ,i. I and I are codominant, and i is recessive. A B A B • Rh –single gene w/ 2 alleles. Ex. Rh(+) has the antigen and Rh(-) does not have the antigen. Blood Types • There are 4 possible blood types: • A, B, AB, O Genotypes I ,I I,I I,i I,I I,i i,i Pg. 344, fig. 14-4 A B A A A B B B Phenotypes produce AB (both antigens) produce A produce A produce B produce B produce O (no antigens) Figure 14-4 Blood Groups Section 14-1 Phenotype (Blood Type Genotype Antigen on Red Blood Cell Safe Transfusions To From Human Genetic Disorders Pg. 345, fig. 14-6 • PKU (Phenylketonuria) – One of the first discovered. – Lacks and enzyme that breaks down an amino acid found in milk. – When phenylalanine builds up, it causes mental retardation. – Caused by a recessive allele from both parents. Human Genetic Disorders • Tay-Sachs Disease – Results in nervous system breakdown. – Death in the first few years of life. – Caused by a recessive allele. Human Genetic Disorders • Cystic Fibrosis – Result of a deletion of 3 bases in the middle of the protein sequence which causes the protein to fold improperly. – It messes up the order because bases are removed. – Digestive problems & thick, heavy mucus clogs the lungs. – Caused by a recessive allele. 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. Human Genetic Disorders • Huntington’s Disease – Loss of muscular control and mental deterioration. – Symptoms appear later in middle ages. – Caused by a dominant allele. Human Genetic Disorders • Sickle Cell Anemia – Red blood sell are shaped like sickles. – Shape causes cells to get stuck in the vessels and blood not to flow. – Tissues are damaged and severe weakness. – Linked to malaria in Africa. – Only 1 DNA base is changed in the allele. – Codominant allele. 14-2 Human Chromosomes Chormosomes # 21 and # 22 • The smallest chromosomes. • The first 2 chromosomes to have their sequence identified. • #21 - 32 million DNA base pairs, 225 genes, responsible for ALS (Lou Gehrig’s disease). • #22 – 43 million DNA base pairs, 545 genes, responsible for many genetic diseases, Leukemia, and tumor causing diseases of the nervous system. • Both have spaces on the chromosome that do not code for proteins. These spaces are unstable sites where rearrangements occur. • Genes located close together on the same chromosome are linked and will be inherited together. Sex Linked Genes Genes that are located on the X and the Y chromosomes. Pg. 350, fig. 14-12 • X Chromosome – more than 100 sex linked genetic disorders occur here. • Y Chromosome – smaller and has fewer disorders. • Colorblindness, Hemophilia, & Muscular Dystrophy are expressed in males even if they are recessive. • To appear in a female, it must have 2 copies. • Are passed from fathers to daughters & to then to their sons. Sex Linked Genetic Disorders Colorblindness • Genes are defective on the X chromosome causing the inability to distinguish certain colors. • Red – Green - 1:10 males, 1:100. • Males have 1 X chromosome so all alleles are expressed even the recessive. Sex Linked Genetic Disorders Hemophilia • Problem on the gene that controls blood clotting. • Protein missing. • 1:10,000 males • May lead to death from minor cuts or internal bleeding from bumps. • It can now be treated with injections. Sex Linked Genetic Disorders Duchenne Muscular Dystrophy • Progressive weakening and loss of skeletal muscle. • 1:3,000 males born in U.S. X – Chromosome Inactivation • Since males only have 1 X chromosome, the female has to make adjustments for having 2 X chromosomes. • In females – one X chromosome is randomly turned off. • It forms a dense region in the nucleus called a Barr body. • Males don’t have Barr bodies because their X chromosome is active. • Ex. Calico Cats- X chromosome carries the allele for coat color and can carry more than 1 color. The X chromosome is turned off in many different places causing several colors to appear. Anytime you see a cat with multiple colors, it will most likely be female. Males are only 1 color Chromosomal Disorders Nondisjunction – most common error to occur in meiosis. Pg. 352, fig. 14-15 • “Not coming apart” • If the chromosomes do not pull apart, an abnormal numbers of chromosomes find their way into the gametes throwing off the number and order. • Involves autosomes, sex chromosomes, and homologous chromosomes. Downsyndrome Pg. 353, fig. 14-16 • An extra copy of chromosome # 21(3 copies – trisomy) • 1:800 babies in the U.S. • Produces mild – severe mental retardation. Sex Chromosome Disorders Caused by Nondisjunction • Turner’s syndrome – female inherits only 1 X chromosome. Women is sterile & her sex organs don’t develop. • Klinefelter’s syndrome – extra X chromosome interferes with meiosis & prevents reproduction. Ex. XXXY, XXXXY. • As long as a Y is present, the offspring will be male. Nondisjunction Section 14-2 Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II 14-3 Human Molecular Genetics DNA Fingerprinting – individuals are identified by analyzing sections of DNA. • No 2 people, except identical twins, have exactly the same DNA. • Determine whether blood, sperm, hair, or other materials left at crime scene matches suspects. • 1990- Human Genome Project – Goal was to identify the DNA sequence for the entire DNA in a human cell. • 2000- Human Genome was sequenced by looking for overlapping regions b/w sequenced DNA fragments. Locating Genes Section 14-3 Gene Sequence Promoter Start signal Gene Stop signal 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. 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. Human Genome • Able to find causes of genetic disorders. • Used to cure genetic disorders by using gene therapy. • It cannot tell if an allele is dominant or recessive.