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Howe Great Union Rags http://www.pedigreeq uery.com/howe+grea t http://www.pedigreeq uery.com/union+rags The Sphynx cat, is a rare breed. It is sometimes known as the Canadian Hairless, originating in Ontario, Canada in 1966, when a black and white house cat gave birth to a male hairless kitten, similar to the Mexican Hairless. Nature periodically produces naturally hairless cats. In 1930, Dr Clyde Keller developed Himalayan Cat breed by crossing between Siamese and Persian Chapter 8 Mendel and Heredity Quick Review p. 161 DNA from the beginning http://www.dnaftb.org/ Origins of Genetics Heredity – the passing of characters from parents to offspring – was one of the greatest mysteries of science Gregor Johann Mendel, Austrian monk, who carried out experiments on garden pea – first to develop rules that accurately predict patterns of heredity Genetics - the branch of biology that focuses on heredity Mendel repeated experiments of a British farmer, T.A. Knight Cross – refers to the mating or breeding two individuals Knight used garden peas Mendel counted the number of each kind of offspring & analyzed the data Useful Features in Peas Several characters of the garden pea (Pisum sativum) exist in two clearly different forms Character – used to mean inherited characteristics, flower color Trait – to a single form of a character, purple flower Male & female reproductive parts of garden peas are enclosed within the same flower – helping control mating Self-fertilization – fertilize itself Cross fertilizationtransfer the pollen from flower to another Stamens – male reproductive organs that produce pollen Pistil – female reproductive part that produces eggs Garden pea is small, grows easily, matures quickly, and produces many offspring Results can be obtained quickly, and there are plenty of subjects to count Traits Expressed as Simple Ratios Mendel initial experiments were monohybrid crosses Monohybrid cross – a cross that involves one pair of contrasting traits His experiments had 3 steps: Step 1: allowed each variety to self-pollinate for several generations True-breeding – all the offspring would display only one form of the character P generation (parental generation) – the first two individuals that are crossed in a breeding experiment Step 2 - Mendel crosspollinated two P generation plants that had contrasting traits Offspring were called filial generation or F1 generation Examined and recorded the number of F1 plants expressing each trait Step 3 – Mendel allowed the F1 to self-pollinate Called the offspring of the F1 generation the second filial generation or F2 generation Each F2 generation was characterized and counted Mendel’s Results The F1 generation showed only one form of the trait When F1 generation was allowed to selfpollinate, the missing trait reappeared in some of the plants A ratio is a comparison of two numbers and can be written as a fraction (705/224) or with a colon 705:224 Homework Write the questions with the answers P. 165 section 1 review 1-6 P. 184 1,6,7 Section 2 Mendel’s Theory A Theory of Heredity Before Mendel, many people thought offspring were a blend of the traits of their parents Mendel correctly concluded that each pea has two separate “heritable factors” Gametes fuse during fertilization, the offspring has two factors for each character, one from each parent Mendel’s Hypotheses Four Hypotheses Mendel developed – foundation of genetics 1) For each inherited character, an individual has two copies of the gene – one from each parent 2) There are alternative versions of genes – now called alleles – different versions of a gene 3) When two different alleles occur together, one of them may be completely expressed, while the other may have no observable effect on the organism’ appearance Dominant – the expressed form of the character – Recessive – the trait that was not expressed when the dominant form was present – 4) When gametes are formed, the alleles for each gene in an individual separate independently of one another. Thus, gametes carry only one allele for each inherited character. When gametes unite during fertilization, each gamete contributes one allele. Because of the way gametes are produced during meiosis Mendel’s Findings in Modern Terms Letters are often used to represent alleles Dominant alleles are indicated by writing the first letter of the character as capital letter Recessive alleles are also indicated by writing the first letter of the dominant trait, but the letter is lowercase Homozygous- two alleles of a particular gene present in an individual are the same – recessive trait is always homozygous, but a dominant may not be ex. TT - tall Heterozygous – the alleles of a particular gene present in an individual are different Tt - tall Since only the dominant allele is expressed, you can not tell if an organism is homozygous or heterozygous Genotype – the set of alleles that an individual has for a character Phenotype – the physical appearance of a character; determined by which alleles (genotype) are present The Laws of Heredity Law of Segregation – the two alleles for a character segregate (separate) when gametes are formed Law of Independent Assortment Mendel conducted dihybrid crosses to study how different pairs of genes are inherited Dihybrid cross – a cross that considers two pairs of contrasting characters Mendel found that for the characters he studied, the inheritance of one character did not influence the inheritance of any other character Law of Independent assortment – that the alleles of different genes separate independently of one another during gamete formation This law applies only to genes that are located on different chromosomes or are far apart on the same chromosome Mendel called the traits “factors” Today we call them genes – units of heredity are portions of DNA, which are found on the chromosomes that are inherited from its parents Homework Section 2 Review p. 169 restate or rewrite the questions 1-4,6 Chapter Review p. 184 & 185 5,8,9, 13, 16 Section 3 Studying Heredity Punnett Squares Breeders must be able to predict how often a trait will appear “ Expected” results of genotypes or phenotypes in a cross is to use a Punnett square Punnett square- a diagram that predicts the outcome of genetic cross by considering all possible combinations of gametes in the cross Named for Reginald Punnett The possible gametes that one parent can produce are written along the top of the square The possible gametes that the other parent can produce are written along the left side of the square Each box inside the square is filled in with two letters by combining the allele from the top and side The letters in the boxes indicate the possible genotypes of the offspring One pair of Contrasting Traits Monohybrid cross – a cross that considers one pair of contrasting traits between two individuals Punnett square can be used to predict outcome between a homozygous purple flower with a homozygous white flower (P generation) All F1 generation is purple and heterozygous Punnett square can also predict the results of a cross of two heterozygous F1 generations Genotype: ¼ homozygous (RR); ½ heterozygous (Rr); ¼ homozygous (rr) Ratio would be 1:2:1 Phenotype: ¾ purple; ¼ white Ratio would be: 3:1 Punnett square allow direct and simple predictions about outcomes Synpolydactyly HOH gene defect semidominant Determining Unknown Genotypes Breeders need to know if a breeding organism is homozygous or heterozygous Test Cross – crossing an individual whose phenotype is dominant, but whose genotype is not known, with a homozygous recessive individual B = black b = white If all the offspring are purple, then the genotype of the unknown individual is PP and all the offspring will be Pp If ½ of the offspring are purple and ½ are white then the genotype of unknown individual is Pp and ½ of the offspring will be Pp and ½ will be pp Outcomes of Crosses Probability – the likelihood that a specific event will occur Can be expressed in words, as decimals, as percentages, or as fractions; we’ll use fractions or ratios Probability = Number of one kind of possible outcome total number of all possible outcomes Racing Game with One Die http://www.shodor.org/interactivate/activi ties/RacingGameWithOneDie/ To find the probability of two independent events that occur in sequence, find the probability of each event occurring separately, and then multiply the probabilities. This multiplication rule is defined symbolically below. Note that multiplication is represented by AND. Multiplication Rule 1: When two events, A and B, are independent, the probability of both occurring is: P(A and B) = P(A) · P(B) Probability of a specific Allele in a Gamete Same formula can be used to predict the probability of an allele being present in a gamete If the alleles are the homozygous, then the probability would be ___ If the alleles are heterozygous, then the probability would be ___ Probability of the Outcome of a Cross Both parents must be considered when calculating the probability of the outcome of a genetic cross Tossing two coins at the same time To find the probability that a combination of two independent events will occur multiply the separate probabilities of the two events ½x½=¼ Inheritance of Traits Pedigree – a family history that shows how a trait is inherited over several generations Helpful if a trait causes a genetic disorder Carriers are individuals who are heterozygous for an inherited disorder, but do not show symptoms of the disorder Carriers can pass the allele for the disorder to their offspring Autosomal or Sex-linked If a gene is autosomal, it will appear in both sexes equally If a trait is sex-linked, its effects are usually seen only in males Sex-linked gene’s allele is located only on the X or Y chromosome Most sex-linked genes are carried on the X chromosome and are recessive Sex-linked traits Red-green color blindness Fragile X syndrome Hemophilia Duchenne muscular dystrophy Boys inherit from mother Dominant or Recessive? Heterozygous or Homozygous? Autosomal dominant, every individual with the condition will have a parent with that condition Homozygous or heterozygous dominant, the trait will show up Noonan Syndrome – genetic disorder that prevents normal development of various parts of the body Recessive Autosomal Traits Cystic fibrosis – Caucasean population Sickle cell anemia – Black population Tay-Sachs – Eastern European AshkenaziJewish population Alpha thalassemia – oriental population Everybody carries 6-8 recessive genes which don’t function well Your Genes Your Health http://www.ygyh.org/ Homework Section review p. 176 1-5 rewrite or restate questions Chapter review p. 184 -185 rewrite or restate the questions 3,10,11,14 Standardized Test Prep (STP) 1-3 Section 4 Complex Patterns of Heredity Complex Patterns of Heredity Polygenic inheritance – when several genes influence a character Eye color, skin color, height, weight, hair color Incomplete dominance – an individual displaying a phenotype that is intermediate between the two parents Characters Controlled by Genes with Three or More Alleles Multiple alleles – genes with three or more alleles ex blood type which is determined by three alleles IA,IB,i A & B are dominant over O, but not dominant over each other, they are codominant Four different blood types: A, B, AB, O Characters with Two Forms Displayed at the Same Time When two dominant alleles are expressed at the same time – codominance Different from incomplete dominance because both traits are displayed Characters Influenced by the Environment AN individual’s phenotype often depends on conditions in the environment Hydrangea - acid soilblue flowers; neutral to basic soil-pink flowers Temperature affects the arctic fox, Siamese cats, and gender of crocodile Humans internal & external influences Genetic Disorders The harmful effects produced by inherited mutations are called genetic disorders Sickle Cell Anemia – caused by a mutated allele that produces a defective form of the protein hemoglobin Recessive allele helps protect the cells of heterozygous individuals from the effects of malaria Cystic Fibrosis (CF) most common, fatal, hereditary, recessive disorder among Caucasians One in 25 Caucasian individuals has at least one copy of a defective gene 1 in 2500 Caucasian infants in the US is homozygous for the cf allele Hemophilia Impairs the blood’s ability to clot Sex-linked trait Occurs more in males Huntington’s Disease (HD) A genetic disorder caused by a dominant allele located on an autosome First symptoms – mild forgetfulness and irritability – thirties or forties Causes loss of muscle control, uncontrollable physical spasms, severe mental illness, and eventually death The disease is unknowingly passed on from one generation to the next Treating Genetic Disorders Genetic counseling - a form of medical guidance that informs people about genetic problems that could effect them or their offspring PKU - required testing of all newborns – can cause severe mental retardation if not treated Gene therapy – modify genetic material of living cells for therapeutic purposes Homework Section 4 review p. 182 rewrite or restate questions 1-6 Chapter review p. 184-185 rewrite or restate questions 4,12,17