遺傳學(xué)概念及理論英文版-資料下載頁
2025-01-18 20:41本頁面
【正文】 neither harmful nor helpful to anism ?Mutations can occur in 2 ways: chromosomal mutation or gene/point mutation Chromosomal mutation: ? less mon than a gene mutation ? more drastic – affects entire chromosome, so affects many genes rather than just one ? caused by failure of the homologous chromosomes to separate normally during meiosis ? chromosome pairs no longer look the same – too few or too many genes, different shape ? Examples: Down’s syndrome – (Trisomy 21) 47 chromosomes, extra chromosome at pair 21 Turner’s syndrome – only 45 chromosomes, missing a sex chromosome (X) Girls affected – short, slow growth, heart problems Klinefelter’s syndrome – 47 chromosomes, extra X chromosomes (XXY) Boys affected – low testosterone levels, underdeveloped muscles, sparse facial hair ? Having an extra set of chromosomes is fatal in animals, but in plants it makes them larger and hardier. Hardier Gene or Point Mutation ? most mon and least drastic ? only one gene is altered ? Examples: Recessive gene mutations: Sickle cell anemia – red blood cells are sickle shaped instead of round and cannot carry enough oxygen to the body tissues – heterozygous condition protects people from malaria Cystic fibrosis – mucous builds up in the lungs TaySachs Disease – deterioration of the nervous system – early death Mutated genes produce enzymes that are less effective than normal at breaking down fatty cell products known as gangliosides. As a result, gangliosides build up in the lysosomes and overload cells. Their buildup ultimately causes damage to nerve cells. Phenylketonuria (PKU) – an amino acid mon in milk cannot be broken down and as it builds up it causes mental retardation – newborns are tested for this Dominant gene mutations: Huntington’s disease – gradual deterioration of brain tissue, shows up in middle age and is fatal Dwarfism – variety of skeletal abnormalities Detecting Geic Disorders ? picture of an individual’s chromosomes – karyotype ? amniotic fluid surrounding the embryo is removed for analysis – amniocentesis Female with Down’s syndrom
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