5&6.Inheritance.ppt - Inheritance and Genetics Basic Patterns of Inheritance • characteristics from parents are transferred to offspring •

5&6.Inheritance.ppt - Inheritance and Genetics Basic...

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Unformatted text preview: Inheritance and Genetics Basic Patterns of Inheritance • characteristics from parents are transferred to offspring • inherited characteristic is not "blended" • dominant • recessive Mendel's Laws of Inheritance (mid 1800's) 1. Equal Segregation "2 copies of a gene separate during meiosis into different gametes" P = purple (dominant) p = white (recessive) Punnett square Mendel's Laws of Inheritance 2. Independent Assortment "genes are segregated and inherited independently of other genes" Color and texture R = round r = wrinkled Y = yellow y = green Exceptions to Mendel's Laws 1. Incomplete Dominance/ Codominance 2. Modifier Genes/ Polygenic Inheritance 3. Environmental Influences Exceptions to Mendel's Laws 1. Incomplete dominance: Heterozygotes phenotype is intermediate Codominance: Heterozygotes express both alleles Chestnut (CC) Palomino (Cc) Cremello (cc) Incomplete dominance in four o’clocks Exceptions to Mendel's Laws 2. many phenotypes depend upon multiple genes Black (BB, Bb) Brown (bb) White (cc + BB, Bb or bb) Multiple alleles in rabbits Polygenic Trait • Eye color is determined by the amount of melanin • Heterochromia iridium • Heterochromia iridium results from alteration to one of the genes. – inherited trait, trauma, medications Gene interaction Epistasis in Labrador retrievers Exceptions to Mendel's Laws 3. environment can have an effect on genes • temperature – dark = low – light = high typically colder • Norm of reaction – Range of phenotypic possibilities from a single genotype under different environmental conditions – Example height Polygenic inheritance in human skin pigmentation Human Genetics Human Genetics 23 pairs of chromosomes 1739 genes/chromosome 8,388,608 genes Human Genetics 23 pairs of chromosomes 1739 genes/chromosome 8,388,608 genes 40,000 – 80,000 genes Gender male = XY Female = XX Inherited Genetic Diseases Inherited Recessive Genetic Diseases Heterozygote Advantage Sex-Linked inherited Genetic Diseases • X-linked • Y-linked X-linked red-green colorblindness Non-Sex Linked Genetically Inherited Human Diseases • Autosomal Recessive Disorders – Symptoms show in homozygous recessive • Autosomal Dominant Disorders – Symptoms show with just 1 allele Autosomal Recessive • • • Cystic Fibrosis – cc Tay-Sachs – tt Sickle – Cell – ss autosomal recessive genetic disorders • Tay-Sachs disease – relentless deterioration of mental and physical abilities that commences around six months of age and usually results in death by the age of four • Cystic fibrosis – Is a common disease which affects the entire body, causing progressive disability and often early death. Symptoms include difficulty breathing, increased mucus production, sinus infections, poor growth and infertility. • Sickle-cell disease (SCD) – characterized by red blood cells that assume an abnormal, rigid, sickle shape. Sickling decreases the cells' flexibility and results in a risk of various complications. Some symptoms include chronic pain, decreased immunity, increased risks of stroke and heart failure, kidney failure. Autosomal Dominant • Achondroplasia – AA is lethal!!! – Aa = dwarfism – aa = no dwarfism • Polydactyly – AA or Aa = extra digits • Progeria – Premature aging • Huntington’s chorea – progressive neurodegenerative genetic disorder, which affects muscle coordination and leads to cognitive decline and dementia. It typically becomes noticeable in middle age. is much more common in people of Western European descent than in those from Asia or Africa. • Marfan’s syndrome – is a genetic disorder of the connective tissue. This syndrome can run from mild to severe. The most serious complications are the defects of the heart valves and aorta. It may also affect the lungs, eyes, the dual sac surrounding the spinal cord, skeleton and the hard palate. Heterozygote Advantage???? • Sickle Cell – Malaria • Cystic Fibrosis – Cholera • Tay Sachs – Tuberculosis Heterozygote Advantage???? Hh Hh + H Homozygous Dominant h H HH Hh h Hh hh Homozygous Recessive Pedigree Analysis • A pedigree is a diagram of family relationships – uses symbols to represent people and lines to represent genetic relationships. • These diagrams make it easier to visualize relationships within families. • Pedigrees are used to determine the mode of inheritance of genetic diseases. • Characteristics of a dominant pedigree are: – 1) Every affected individual has at least one affected parent – 2) Affected individuals who mate with unaffected individuals have a 50% chance of transmitting the trait to each child – 3) Two affected individuals may have unaffected children. • Characteristics of recessive pedigrees are: – 1) An individual who is affected may have parents who are not affected – 2) All the children of two affected individuals are affected – 3) In pedigrees involving rare traits, the unaffected parents of an affected individual may be related to each other. Pedigree Analysis • cystic fibrosis (recessive genetic disease) Aa Aa Aa Aa AA aa Aa Aa aa Aa Aa Aa Pedigree Analysis • congenital generalized hypertrichosis (CGH) • dominant or recessive? • X-linked? CGH Pedigree (Aa) AA AA AA dominant or recessive? Punnett Square (recessive) A A a Aa Aa a Aa Aa recessive in F1? CGH Pedigree (Aa) AA AA AA dominant or recessive? CGH Pedigree (Aa) Xa Y X A Xa XaY XaXa X-linked? Punnett Square (X-linked) X Y a X XX XY X XX XY A a A a a a A a who is affected? CGH Pedigree (Aa) Xa Y X A Xa Xa Xa Xa Y XA Xa XAY XaXa X-linked? CGH Pedigree (Aa) Xa Y X A Xa Xa Xa Xa Y XA Xa XAY XaXa X-linked – most likely. ...
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