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Human Chromosomes Learning Objectives Identify the types of human chromosomes in a karyotype. Describe the patterns of the inheritance of human traits. Explain how pedigrees are used to study human traits. What makes us human? To find out what makes us human we have to look deeper into a cell…we have to look at the human genome. Genomes A genome is the full set of genetic information that an organism carries in its DNA. (genes are on chromosomes) The analysis of any genome starts with chromosomes. A human karyotype Karyotypes To see human chromosomes scientists analyze chromosomes during mitosis and arrange the in a picture called a karyotype A karyotype shows the complete diploid set of chromosomes grouped together in pairs, arranged in order of decreasing size. Sex Chromosomes Two of the chromosomes in the human genome are sex chromosomes. Females: two X chromosomes Males: one X chromosome Sex Chromosomes More than 1200 genes are found on the human X chromosome. The human Y chromosome contains only about 140 genes. Autosomal Chromosomes The other 22 pairs of non-sex chromosomes are called autosomal or autosomes. Male = 46, XY Female = 46, XX Transmission of Human Traits Many human traits follow a pattern of simple dominance. For example, the gene MC1R helps determine skin and hair color. Some of MC1R’s recessive alleles produce red hair. An individual with red hair usually has two of these recessive alleles. Complex Inheritance and Human Heredity A dominant genetic disorder is expressed with ONE dominant allele present Complex Inheritance and Human Heredity Recessive Genetic Disorders A recessive trait is expressed when the individual is homozygous recessive for the trait. Transmission of Human Traits The alleles for many human genes display codominant inheritance. Transmission of Human Traits The X and Y chromosomes determine sex. The genes located on them show sex linkage. Complex Inheritance and Human Heredity Sex-Linked Traits Genes located on the X chromosome Red-green color blindness Hemophilia Sample problem: In fruit flies, the gene for white eyes is sex-linked recessive. (R) is red and (r) is white. Cross a white-eyed female with a normal red-eyed male Pearson video Given the complexities of genetics, how would you go about determining whether a trait is caused by a dominant or recessive allele and whether the gene for that trait is autosomal or sex-linked? How would you analyze the pattern of inheritance followed by a particular trait? Human Pedigrees A pedigree chart shows the relationships within a family. A female A marriage Expresses the trait A male Parents to children Does not express the trait Analyzing a Pedigree The information from pedigree analysis makes it possible to determine the nature of genes and alleles associated with inherited human traits. Complex Inheritance and Human Heredity Pedigrees can have the following inheritance patterns: Autosomal dominant Autosomal recessive X-Linked A = the trait (a genetic disease or abnormality, dominant) a = normal (recessive) Can we determine the Genotypes of all the individuals? What are the genotypes? What is the inheritance pattern? A = the trait (a genetic disease or abnormality, dominant) a = normal (recessive) What are the genotypes? What is the inheritance pattern? What are the genotypes? What is the inheritance pattern? What are the genotypes? What is the inheritance pattern? Summary of Human Chromosomes A karyotype shows the complete diploid set of chromosomes. Human traits follow patterns of inheritance. Pedigree analysis determines the nature of genes and alleles associated with human traits. Human Genetic Disorders Learning Objectives Explain how small changes in DNA cause genetic disorders. Summarize the problems caused by nondisjunction. From Molecule to Phenotype Changes in the DNA sequence of a gene can change proteins: Altering amino acid sequences Affecting the phenotype Sickle cells Cystic Fibrosis Most cases result from the deletion of three bases in the DNA of a single gene Body does not produce normal CFTR Missing Genetic Advantages Some alleles that cause disease may also have benefits. Carrying one copy of the sickle cell provides protection from malaria. Carrying one copy of the CF allele provides protection from typhoid bacterium. Chromosomal Disorders: Nondisjunction Nondisjunction: when homologous chromosomes do not separate as they should Gametes with an abnormal number of chromosomes may result. Down Syndrome The most common form of trisomy, involving three copies of chromosome 21, is Down syndrome. Other Chromosomal Disorders Nondisjunction of the X chromosomes can lead to a disorder known as Turner’s syndrome. In males, nondisjunction may cause Klinefelter’s syndrome. Human Genetic Disorders Summarized Small changes in a gene’s DNA sequence can change proteins and may affect phenotype. Nondisjunction may cause gametes with an abnormal number of chromosomes. Studying the Human Genome Learning Objectives Summarize the methods of DNA analysis. State the goals of the Human Genome Project and explain what we have learned so far. Manipulating DNA By using tools that cut, separate, and then replicate DNA base by base, scientists can now read the base sequences in DNA from any cell. Read Cut Separate Cutting DNA DNA molecules must be cut into smaller pieces for analysis. Restriction enzymes cut DNA molecules into restriction fragments. Separating DNA Gel electrophoresis is used to separate and analyze the differently sized fragments of DNA. Reading DNA Single-stranded DNA fragments are placed in test tubes with DNA polymerase and the nucleotide bases A, T, G, and C. C A C G T Gel electrophoresis video The Human Genome Project The Human Genome Project was a 13-year, international effort with the main goals of: Sequencing all 3 billion base pairs of human DNA Identifying all human genes Sequencing Genes Once DNA strands are marked, “shotgun sequencing”can be used. Computer programs: Find areas of overlap Link overlapping areas Align fragments Identifying Genes By locating promoters, scientists can identify genes. After a promoter is an open reading frame. Sharing Data Bioinformatics combines molecular biology with information science. It is critical to studying and understanding the human genome. What We Have Learned The Human Genome Project identified: • genes and sequences in those genes that are associated with diseases and disorders • there are 3 million locations where single-base DNA differences occur New Challenges: What’s Next? The Human Genome Project has raised ethical and legal questions. Many sequencing projects are underway, helped by new technologies. Gene Expression and Chromatin Chromatin must be less compact for transcription to occur. This depends on the presence or absence of chemical markers that bind to nucleosomes. Summary of Studying the Human Genome Scientists can read the base sequences in DNA with tools that cut, separate, and replicate DNA base by base. The Human Genome Project was an effort to sequence base pairs of human DNA and identify human genes. Cracking the Code Video Segment