Human Genome

The Human Genome Chapter 14 Karyotypes All organisms have their own characteristic number of chromosomes in every cell nucleus of somatic cells. To analyze the chromosomes, a picture is taken of them during mitosis (Why then?) and analyzed. The picture is cut apart and pieced together to pair up homologous chromosomes to create a karyotype. 44 of the chromosomes are autosomes, 2 are sex chromosomes. Females have 2 x’s. Males have an x and y. All egg cells have x chromosomes. Half of sperm cells have x and half have y. Pedigree Charts Pedigree charts can be created for related individuals to infer genotypes of family members. These can be used by genetic counselors to predict the and Blood Group Genes Blood types ABO are based on several alleles. There are 3 genes: IA , IB , i IA and IB are codominant. IA produces A antigens, IB produces B antigens. i is recessive. i produces no antigens. IAIA and IAi are blood type A IB IB and IB i are blood type B IA IB is blood type AB is the universal recipient ii is the universal donor Rh is controlled by one gene. There is a positive and negative alternative. Positive is dominant. Recessive Alleles Phenylketonuria or PKU is caused by recessive alleles on chromosomes 12. An individual homozygous for this trait cannot break down the amino acid phenylalanine. Babies born with this trait who go undetected will build up the amino acid in tissues which results in mental retardation. A test done after birth will detect this trait and a diet low in the amino acid will correct the problem. Tay-Sachs disease is also caused by a recessive autosomal allele. A homozygous individual will die in childhood from nervous system breakdown. No cure is available, but genetic testing is available to indicate the presence to prospective parents. Cystic fibrosis is also caused by a recessive allele on chromosome 7. The cause of problems associated with the disease is change in the protein synthesis that is directed by the faulty allele. Dominant Alleles Huntington’s disease, a progressive nervous system disorder, is the result of a dominant allele. People with this disorder are usually not aware until they reach their thirties. Codominant Alleles Sickle cell anemia is the result of codominant alleles. A person who is heterozygous for the trait is healthy and resists malaria. Someone is homozygous will display the symptoms of the disease. Sex-linked Genes • Associated mainly with the X chromosome • A recessive allele on an x chromosome in a male will be expressed because nothing on the Y will counter it. • Females need to recessive alleles for the trait to become evident. o Colorblindness o Hemophilia o Duchenne Muscular dystrophy X Chromosome Inactivation X chromosome is randomly switched off in females, one at a times. In males, it stays on. Example is spotted cat color. Males can have only one color spot. Females can have 3 different colors. Chromosomal Disorders Abnormal numbers of chromosomes can occur when homologous chromosomes fail to separate correctly in meiosis I. • Downs Syndrome is from trisomy of chromosomes 21. • Turners Syndrome is from female inheriting only one X chromosome. She would be sterile. • Klinefelter’s Syndrome is in males when they get too many X chromosomes. Applications of Genetics to Life • Prenatal genetic testing • DNA fingerprinting • Human Genome Project • Gene therapy