* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download The Human Genome Chapter 14
Nutriepigenomics wikipedia , lookup
Gene therapy wikipedia , lookup
Extrachromosomal DNA wikipedia , lookup
Human genetic variation wikipedia , lookup
Therapeutic gene modulation wikipedia , lookup
Gene expression profiling wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Minimal genome wikipedia , lookup
Genome evolution wikipedia , lookup
Human genome wikipedia , lookup
Gene expression programming wikipedia , lookup
Epigenetics of neurodegenerative diseases wikipedia , lookup
Cell-free fetal DNA wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Public health genomics wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Genetic engineering wikipedia , lookup
Medical genetics wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Genomic imprinting wikipedia , lookup
Point mutation wikipedia , lookup
Skewed X-inactivation wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
History of genetic engineering wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Designer baby wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Y chromosome wikipedia , lookup
Microevolution wikipedia , lookup
Neocentromere wikipedia , lookup
The Human Genome Chapter 14 By: Nick Thompson Biology Period 4 May 5, 2009 Section 1- Human Heredity • • • • Scientists begin answering the question about what makes us human by seeing the human cell with a microscope, starting with the chromosomes. The cell biologists photograph the cells in mitosis to analyze the chromes. A picture of chromosomes arranged in pairs is known as a karyotype. Two of the 46 chromosomes in a typical human body cell are called sex chromosomes. They determine the individual’s sex. The remaining 44 chromosomes are called autosomes. All human egg cells carry a single X chromosome (23,X). However, half of all sperm cells carry an X chromosome and half carry a Y chromosome (23,Y). This means that half of the zygotes will be 46,XX and half will be 46, XY. Section 1-Continued • • • • • Human genes are inherited by the same principles Gregor Mendel discovered with his work on garden peas. A pedigree chart shows the relationship within a family. It is fittingly used to study how the trait is passed from one generation to the next. The human genome – our complete set of genetic information. It was “a major scientific undertaking” when it was discovered. Blood Group Genes- knowing a person’s blood group is crucial for procedures like blood transfusion because, putting the wrong type of blood into a patient during a transfusion could be fatal. The best known groups are the ABO and the Rh blood groups. Rh- stands for “rhesus monkey.” It is determined by single gene with 2 alleles- positive and negative. ABO-Three alleles I^a, I^b, and i. Those who are homozygous for the i allele (ii) produce no antigen and are said to have blood type O. Section 1 cont. • • • • In most cases, the presence of a normal functioning gene is revealed only when an abnormal or nonfunctioning allele affects the phenotype. One of the first genetic disorders to be understood this way was phenylketonuria, or PKU. People with PKU lack the enzyme that is needed to break down phenylalanine. Phenylalanine is an amino acid found in milk and many other foods. Not all genetic disorder are caused by recessive alleles. If you have a dominant allele for a genetic disorder, it will be expressed. Two examples of genetic disorders caused by autosomal dominant alleles are a form of dwarfism known as achondroplasia and a nervous system disorder known as Huntington’s disease. Section 1 cont. • • • 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. Cystic Fibrosis is most common among people whose ancestors came from Northern Europe. The disease is caused by a recessive allele on chromosome 7. Most cases of cystic fibrosis are caused by the deletion of 3 bases in the middle of a sequence for a protein. This protein normally allows chloride ions to pass across biological membranes. The deletion of these 3 bases removes just one amino acid from this large protein, causing it to fold improperly. Because of this, the cells do not transport the protein to the cell membrane, and the misfolded protein is destroyed. People with one normal copy of the allele are unaffected, because they can produce enough of the chloride channel protein to allow their tissues to function properly. Section 1 cont. • • • • Sickle cell disease, a serious disorder found in about 1 out of 500 African Americans, is caused by a codominant allele. Sickle cell shaped red blood cells are more rigid than normal cells and tend to get stuck in the capillaries, the narrowest blood vessels in the body. As a result, blood stops moving through these vessels, damaging cells tissues, and organs. Sickle cell disease produces physical weakness and damage to the brain, heart, and spleen. In some cases, it may be fatal. Hemoglobin is the protein in red blood cells that carries oxygen. The normal allele – just one DNA base is changed. This change substitutes the amino acid valine for glutamic acid. As a result, th abnormal hemoglobin is somewhat less soluble than normal hemoglobin. Low oxygen levels cause some red blood cells to become sickle shaped. Section 2- Human Chromosomes • Intro – The average human gene consists of about 3000 base pairs, while the largest gene in the human has more than 2 million base pairs. • Human Genes and Chromosomes – Chromosomes 22 contain as many as 545 different genes, some of which are very important for health. Genetic disorder on chromosome 22 include and allele that causes a form of leukemia and another associated with neurofibromatosis, a tumor causing disease of the nervous system. Human Genes and Chromosomes Continued • However, chromosome 22 also contains long stretches of repetitive DNA that do no code for proteins. These long stretches of a repetitive DNA are unstable sites where rearrangement can occur. The structure of chromosome 21 is similar. It contains about 225 genes, including one associated with amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease. Chromosome 21 also has many regions with no genes at all. Sex-linked Genes • Chromosomes determine sex, genes located on them are said to be sex-linked genes. • More than 100 sex-linked disorders have now been mapped to the X chromosome. • The human Y chromosome is much smaller than the X chromosome and contains only a few genes. Colorblindness A sex-linked disorder • • • • • • • Three human genes associated with vision are located on the X chromosome. In males a defective version of this can mean colorblindness. The most common form of this disorder, red-green colorblindness, is found in the U.S. Colorblindness is rare in females, only about 1 in 100 females have colorblindness. All the X linked alleles are expressed in males, even if they are recessive. In order for a recessive allele to be expressed in females, there must be two copies of the allele, one on each of the two Xchromosomes. The recessive phenotype of a sex-linked genetic disorder tends to be much more common among males than among females. Men pass their X chromosomes along to their daughters, sex linked genes move from fathers to daughters and possibly to the daughters sons. Hemophilia • • • • • • • Two important genes carried on the X chromosomes help control blood clotting. A recessive allele in either of these two genes may produce a disorder called hemophilia. In hemophilia, a protein necessary for normal blood clotting is missing. About 1 in 10,000 males are born with a form of hemophilia. People with hemophilia can bleed to death from a minor cut and can suffer internal bleeding from a bruise or bump. Hemophilia can be treated by injections of normal blood clotting proteins, Which are now produced using recombinant DNA. Duchenne Muscular Dystrophy Sex-Linked Disorder • • • • • Duchenne Muscular Dystrophy is a disorder that results in the progressive weakening and loss of skeletal muscle. In the U.S., 1of every 3,000 males is born with this condition. Duchenne muscular dystrophy is caused by a defective version of the gene that codes for a muscular protein. Researchers in many laboratories are trying to find a way to treat or cure this disorder. Its possible by inserting a normal allele into the muscle cells of Duchenne muscular dystrophy patients. X-Chromosome Inactivation • • • • • In female cells, one X chromosome is switched off. That turned off chromosome forms a dense region in the nucleus known as Barr body. Barr bodies are generally not found in males because their X chromosome is still active. In cells in some parts of the body, one X chromosome is switched off. In other parts of the body the other X chromosome is switched off. Chromosomal Disorders • • • The most common error in meiosis occurs when homologous chromosomes fail to separate. This is known as nondisjunction, which means “not coming apart.” If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes, and a disorder of chromosome numbers may result. Down Syndrome • • • • • • If two copies of an autosomal chromosome fail to separate during meiosis, an individual may be born with tree copies of a chromosome. This is known as a trisomy, meaning “three bodies.” The most common form of trisomy involves three copies of chromosome 21 and is called Down Syndrome. In the U.S., approximately 1 baby in 800 is born with Down syndrome. Down syndrome produces mild to severe mental retardation. It is also characterized by an increased susceptibility to many diseases and a higher frequency of some birth defects. Sex Chromosome Disorders • • • • • • • • Disorders also occur among the sex chromosomes. Two of these abnormalities are Turner’s syndrome an Klinefelter’s syndrome. In females, nondisjunction can lead to Turner’s syndrome usually inherits only one X chromosome. Women with Turner’s syndrome are sterile, which means that they are unable to reproduce. In males, nondisjunction causes Klinefelter’s syndrome. The extra X chromosome interferes with meiosis and usually prevents these individuals from reproducing. Cases of Klinefelter’s syndrome have been found in which individuals were XXXY or XXXXY. There have been no reported instances of babies being born without an X chromosome, indication that the X chromosome contains genes that are vital for the survival and development of an embryo. Section 3Human Molecular Genetics • • • • The Tay-Sachs and Cystic Fibrosis alleles have slightly different DNA sequences form their normal counter parts, a variety of genetic tests have been developed that can spot those differences. DNA testing can pinpoint the exact genetic basis of a disorder, making it possible to development more effective treatment for individuals affected by genetic disease. DNA fingerprinting-Analysis of sections of DNA that have little or no known function, but vary widely from one individual to another, in order to identify individuals. The DNA sequence of the common bacterium “Escherichia Coli,” which was determined in 1996, contains only 4,639,221 base pairs, making it just about as long as this textbook if it were printed on paper in a readable typeface. Section 3 Continued • • • Gene therapy is the process of changing the gene that causes a genetic disorder. The goal of biology is to gain a better understanding of the nature of life. As our knowledge increases, however, so does our ability to manipulate the genetics of living things, including ourselves The End