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Mendelian Genetics
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Artificial Selection Inherited variations in traits
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Mendelian Genetics
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Heredity – The passing of traits from parents to offspring through generations. –Genetics – The study of genes. “Genesis” to be born Genes – Individual bits of information made of DNA and located on chromosomes
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Mendelian Genetics Gregor Mendel – Father of Genetics Austrian monk/mathemetician Experimented with pea plants Mid 1800’s – work was not accepted Work rediscovered in 1900’s
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Pea plants Advantages: 1.Grow quick in a small plot. 2.Easy to cross (mate) 3.Dioecious – both sexes on same plant. 4.Many viable offspring from a variety of crosses
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Pea plants Advantages: 1.Grow quick in a small plot. 2.Easy to cross (mate) 3.Dioecious – both sexes on same plant. 4.Many viable offspring from a variety of crosses
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Pea plants Advantages: 1.Grow quick in a small plot. 2.Easy to cross (mate) 3.Dioecious – both sexes on same plant. 4.Many viable offspring from a variety of crosses male -female
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Pea plants Advantages: 1.Grow quick in a small plot. 2.Easy to cross (mate) 3.Dioecious – both sexes on same plant. 4.Many viable offspring from a variety of crosses
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Pea plants Advantages: 1.Grow quick in a small plot. 2.Easy to cross (mate) 3.Dioecious – both sexes on same plant. 4.Many viable offspring from a variety of crosses
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Pea plants Advantages: 1.Grow quick in a small plot. 2.Easy to cross (mate) 3.Dioecious – both sexes on same plant. 4.Many viable offspring from a variety of crosses
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Pea plants Advantages: 1.Grow quick in a small plot. 2.Easy to cross (mate) 3.Dioecious – both sexes on same plant. 4.Many viable offspring from a variety of crosses
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Differences in Mendel’s study 1.Repeated results 2.Large numbers (in a small space) 3.Limited traits 4.Used readily identified traits and pure varieties
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Probability Dealing with chance The determination of what is most likely to happen Only works for large numbers Each event is independent over another
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Probability Dealing with chance The determination of what is most likely to happen Only works for large numbers Each event is independent over another
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Probability Dealing with chance The determination of what is most likely to happen Only works for large numbers Each event is independent over another Deviation – the difference between the results you expect and the results you actually get.
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Mendel’s studies Pure varieties – Always produce same results and same traits Bred for 10 generations to ensure viability
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X = 6 feet tall
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X = 1 foot tall
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Pure variety cross Pure TallxPure dwarf
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Pure variety cross Pure TallxPure dwarf All Tall
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Pure variety cross Pure TallxPure dwarf All Tallx Tall
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Pure variety cross Pure TallxPure dwarf All Tallx Tall Tall : Dwarf
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Pure variety cross Pure TallxPure dwarf All Tallx Tall Tall : Dwarf 3 : 1 75% : 25%
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Genetic terms Hybrid – Contains both dominant and recessive genes or traits Dominant – Always appears in a hybrid. Capital letter denotes the dominant trait T = Tall Recessive – Never appears in a hybrid. Lower case denotes the recessive trait. t = dwarf
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Genetic terms Phenotype– How the genes appear. Ex. Tall, dwarf, Green, yellow Genotype – Shows the gene combinations present. Ex. TT, Tt, tt Tt = tT (capital 1 st )
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Genetic terms Genotype – Shows the gene combinations present. Ex. TT, Tt, tt Tt = tT (capital 1 st ) Allele – Refers to one of the two forms of a gene. Ex. “T” or “t” locus – the location of an allele on a chromosome
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Genetic terms Genotype – Shows the gene combinations present. Ex. TT, Tt, tt Tt = tT (capital 1 st ) Allele – Refers to one of the two forms of a gene. Ex. “T” or “t” locus – the location of an allele on a chromosome
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Genetic terms Genotype – Shows the gene combinations present. Ex. TT, Tt, tt Tt = tT (capital 1 st ) Allele – Refers to one of the two forms of a gene. Ex. “T” or “t” locus – the location of an allele on a chromosome
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Genetic Crosses Law of Complete Dominance – When a dominant and recessive trait appear in a hybrid. The dominant trait always appears. Capital = Dominant, lower case = recessive Homozygous – Organisms which have the same 2 genes (alleles – letters) for a trait. TT or tt (purebred) Heterozygous – Organisms which have 2 different genes (alleles- letters) for a trait. Tt (hybrid)
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Genetic Crosses Calculating phenotypes and genotypes P 1 = parent generation F 1 = first offspring (filial) F 2 = 2 nd offspring from F 1 cross. Punnett Square – Diagram used to calculate probabilities, genotype, and phenotype from genetic crosses. Right side – father’s alleles – letters Left side – mother’s alleles – letters Each square = offspring (4) = 25%
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25% Gametes Offspring Phenotype = Tall Genotype Phenotype = TallPhenotype = Short Phenotype = Tall 25%
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Haploid - 23 Diploid-46
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Law of segregation: Law of segregation – the 2 alleles for each trait separate when gametes form Haploid - 23 Diploid-46
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25%
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Gametes Offspring Phenotype = Tall Genotype Phenotype = TallPhenotype = Short Phenotype = Tall 25%
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Sample Genetic Problems Solve on Punnett Square Sample # 1 and 2 Tall (T) is dominant over short (t) (recessive) pea plants. Mate a homozygous tall with a homozygous recessive and calculate the genotypes and phenotypes per cents and ratios for the F1 and F2 generations. Round ( R ) seeds are dominant over wrinkled ( r ) seeds. Mate a heterozygous round seed plant with a homozygous wrinkled. Calculate the genotypes, phenotypes, and % and ratios for the F1 generation. Sample # 4 Green (G) is the dominant color for pods in pea plants. Yellow (g) is recessive. Calculate the F1 generation genotypes, phenotypes, % and ratios from a cross between two heterozygous Green podded plants.
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# 3 Round ( R ) seeds are dominant over wrinkled ( r ) seeds. Mate a heterozygous round seed plant with a homozygous wrinkled. Calculate the genotypes, phenotypes, and % and ratios for the F1 generation.
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Sample # 4 Green (G) is the dominant color for pods in pea plants. Yellow (g) is recessive. Calculate the F1 generation genotypes, phenotypes, % and ratios from a cross between two heterozygous Green podded plants.
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4 Chromosomes 2 Chromosomes 1 Diploid Cell 4 Haploid Cells
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Crossing over and Independent assortment
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Haploid - 23 Diploid-46
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25% Gametes Offspring Phenotype = Tall Genotype Phenotype = TallPhenotype = Short Phenotype = Tall 25%
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Test cross To determine an unknown genotype. A known genotype (homozygous recessive) is mated with an unknown (pure or hybrid?) to determine from the results
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Test cross Tall = TT or Tt dwarf = tt A tall plant of unknown genotype is crossed with a dwarf. 2 possible choices
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Dihybrid Cross 2 differents characters with two different traits on different chromosomes
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Dihybrid Cross 2 differents characters with two different traits on different chromosomes Law of Independent Assortment – States that alleles of each gene segregate into gametes independently of alleles of other genes, as shown in a dihybrid cross
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Human Genetics and Exceptions to Mendel’s Studies
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Exceptions to Mendel’s studies Mendel – Traits showed complete dominance (autosomal) with traits on separate homologous chromosomes
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Exceptions to Mendel’s studies 1)Incomplete or Co- dominance – Neither gene is hidden in a hybrid Causes a blending of traits or both traits appear
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Exceptions to Mendel’s studies 1)Incomplete or Co- dominance – Neither gene is hidden in a hybrid Causes a blending of traits or both traits appear Ex. 4 o’clock flower, carnations, shorthorn cattle
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Incomplete Dominance Two different traits. Neither is dominant, so there is a blending of the traits.
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X
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Codominance Two different traits, both are dominant and both appear
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Sample Problem #1 Shorthorn cattle – Red fur = R White fur = R ’ RR x R’R’ = RR’ = Roan (pink) Cross two Roan cattle
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2) Multiple Alleles More than two alleles possible to choose for a trait, but only two alleles present
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Multiple alleles Rabbit fur - 4 possible alleles C = normal c = albino C ch = chinchilla c h = himalayan
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Multiple alleles Rabbit fur - CC = Cc = cc = CC ch = c h c = C ch c h =
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Multiple Alleles – Blood type Human blood Antigens - Foreign clotting factor 3 alleles – I A, I B, i (no antigen) Phenotypes: Type A = I A I A or I A I Type B = I B I B or I Bi Type AB = I A I B Type O = i i
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OO AA BB AO BO AB or
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Sample # 2 Blood type – A woman who is hybrid for type B blood marries a man with type O blood. What type of blood could their children NOT have?
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Chromosomes and Sex determination
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44 Autosomes 2 Sex Chromosomes
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Male Genotype
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44 Autosomes 2 Sex Chromosomes
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Female Genotype
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Probability of Boy vs. Girl? 50:50
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3) Sex-linked Traits Sets of alleles found only on the X chromosome. Females have two alleles X+X, males have only one X+Y
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3) Sex-linked traits Some traits are found on the alleles of only X chromosomes and not on the Y. (Females = XX and Males = XY) First discovered in fruit flies
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Fruit Flies Drosophila melanogaster
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3) Sex-linked traits 1910 – Thomas Morgan Drosophila (fruit flies) white eyed flies – recessive mutation (r) 3/1000 Red eyes = dominant (R) Homozygous cross – all red Hybrid cross = 3:1 ? Results = 3,470:782 with all white eyes being male Traits on X but not Y chromosome
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3) Sex-linked traits 1910 – Thomas Morgan Drosophila (fruit flies) white eyed flies – recessive mutation (r) 3/1000 Red eyes = dominant (R) Homozygous cross – all red Hybrid cross = 3:1 ? Results = 3,470:782 with all white eyes being male Traits on X but not Y chromosome
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Drosophila Fruit Fly Cultures - Chromosome 1, White Drosophila Fruit Fly Cultures - Wild Type (+)- Genetics
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X R = Red eyes X r = white eyes Cross 2 Hybrid red-eyed flies. Calculate the genotypes and phenotypes for male and female offspring Sample # 3
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Sample # 4 Red-Green or Green-Red Colorblindness, Hemophilia X N = Normal trait X n = colorblind A colorblind female marries a normal eyed male. Which offspring will be colorblind?
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Everyone should see a 12.
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Normal visioned people should see 45. Colorblind people won't see any numbers.
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Normal visioned people should see 29. Colorblind people should see 70.
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Normal visioned people won't readily see any number, but colorblind people will easily see a number 5.
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Normal visioned people will see 26. If you are red-blind, you should only clearly see the 6. If you are green-blind, you should only see the 2. A totally colorblind person won't see any number in this plate.
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This is illustrated by calico cats. Coat color in cats is an X-linked gene, with alleles for black and orange-brown, so X B X B and X B Y cats will have a black coat, while X O X O and X O Y will have an orange-brown coat. Another possible combination for female cats would be X B X O. Both of the color alleles would be expressed, so the cat would end up being partially brown and partially black. or only X B X B and X B Y X O X O and X O YXBXOXBXO
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Hemophilia Family Tree
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4) Sex influenced traits Gene present plus the proper hormone required Examples: Male pattern baldness, hairy pinna (ears), horns in sheep.
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5) Polygenic traits More than two alleles on more than two chromosomes, with more than two alleles appearing at once.
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Polygenic traits in humans Non – Blue Eye color Skin color Hair color Height
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Dark Brown eyes Light skin Short Light Green eyes Dark skin Tall
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Non – Blue Eye color Hair color
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Skin color
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Genes and the Environment The environment influences the phenotype for some genotypic traits. The norm of reaction is the phenotypic range of a genotype influenced by the environment For example, hydrangea flowers of the same genotype range from blue- violet to pink, depending on soil acidity Genes are what an organism may become not will become Ex. Genes for chlorophyll – no sunlight = no chlorophyll Human behavior – identical twins - differences
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Acidic soil Basic or alkali soil
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Norms of reaction are generally broadest for polygenic characters Such characters are called multifactorial because genetic and environmental factors collectively influence phenotype Genes and the Environment
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Genetic disorders Pedigree : Chart used to trace family histories of genetic traits
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Hemophilia Family Tree
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Sickle Cell Anemia
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Polydactyly
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PKU Phenylketonuria
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PKU - 1 in 15,000 Americans. A non-food source of phenylalanine is the artificial sweetener Aspartame. This compound, sold under the trade names "Equal" and "NutraSweet", is metabolized by the body into several chemical byproducts including phenylalanine.
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Porphyry ?
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