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S-B-8-1_Heredity PowerPoint Heredity Mendel’s Laws S-B-8-1_Heredity PowerPoint Heredity Source: http://en.wikipedia.org/wiki/Habsburg S-B-8-1_Heredity PowerPoint How are traits inherited? • Selective Breeding – Domestication of plants • Higher yielding crops • Mature faster, set fruit earlier • Attractive fruit Gray Wolf – Domestication of animals • Desired behaviors • Desired qualities http://animal.discovery.com/mammals/wolf/ http://www.akc.org/breeds/ S-B-8-1_Heredity PowerPoint Gregor Mendel • Born in 1822, Brno, Moravia (now the Czech Republic), the only son of a farming family • Showed promise in school and entered the monastery to continue his education • Went to the University of Vienna, studying physics and math • Came back to the Abbey in Brno to teach and experiment in the garden S-B-8-1_Heredity PowerPoint Mendel’s Experiment • Mendel investigates inheritance in pea plants for eight years. • He chose peas because: – They are easy to cultivate. – They reproduced sexually. – They have easy to distinguish traits. http://www.scientificamerican.com/article.cfm?id =gene-behind-mendels-green&ref=rss S-B-8-1_Heredity PowerPoint Pisum sativum-The Pea http://www.tutorvista.com/content/biology/biology-iii/heredity-and-variation/mendels-experiments.php S-B-8-1_Heredity PowerPoint Artificial Pollination Removing Stamen from flower Exposing Stigma and dusting with pollen Covering the flower with bag and labeling stem S-B-8-1_Heredity PowerPoint Monohybrid Cross • Crossed Tall plants with Short plants, the parents or P • Called the hybrid offspring, the First Filial, F1, generation P What would you expect the F1 Generation to look like? All offspring are tall. F1 X S-B-8-1_Heredity PowerPoint Rule of Dominance • DOMINANT traits – The trait expressed in hybrid offspring, the F1 generation • recessive traits – The trait that is not expressed, or hidden, in the F1 generation S-B-8-1_Heredity PowerPoint The F2 Generation Mendel allowed the F1 plants to self pollinate. X P What would you expect the offspring to look like? F1 787 tall plants and 277 dwarf plants F2 S-B-8-1_Heredity PowerPoint Rule of Unit Factors Mendel’s Explanation • Individuals have two “heritable” factors for a trait . • The two factors may or may not contain the same information: X P TT – Homozygous individuals have identical factors . tt F1 • TT or tt Tt – Heterozygous individuals have 2 different factors. • Tt F2 TT Tt Tt tt S-B-8-1_Heredity PowerPoint Genetics Tall allele Genes at the same location Dwarf allele HOMOLOGOUS CHROMOSOMES Modern Genetics • Individuals have two copies of a gene (one on each homologous chromosome). • The various forms of a gene are called alleles: – Dominant alleles are expressed when they are present. – Recessive alleles are expressed only when the individual is homozygous for the gene form. S-B-8-1_Heredity PowerPoint Phenotypes vs. Genotypes • Phenotypes refer to what is expressed or the organism’s outward appearance. – TT and Tt pea plant will be over 6 feet tall. – tt pea plant will be under 2 feet tall. • Genotypes refers to the specific alleles that make up the organism. – A TT pea plant is homozygous Tall while a tt pea plant is homozygous dwarf. – A Tt pea plant is heterozygous Tall. S-B-8-1_Heredity PowerPoint THINK-PAIR-SHARE http://www.countryfarmlifestyles.com/raising-rabbits.html X http://athomepets.blogspot.com/2008/ 03/bunnies-born-for-easter-crowd.html 1. If the black rabbit and the white rabbit were bred and all the offspring were black, what conclusion can you make? 2. If the hybrid offspring were allowed to mate, would you expect some of the litter to be white? Why? S-B-8-1_Heredity PowerPoint THINK-PAIR-SHARE 1. Are the genotypes homozygous dominant, homozygous recessive, or heterozygous? • • • • DdFF RrYy LLww ggSs 2. The letters used in genotypes usually represent the dominant trait, e.g., Y-yellow seed and y-green seed. Decide on traits to represent the genotypes above, and describe the phenotypes. S-B-8-1_Heredity PowerPoint Law of Segregation Mendel’s Explanation • Alleles separate when forming gametes. • Parents pass only one allele for each trait. http://www-bcf.usc.edu/~forsburg/meiosis.html Modern Genetics • What process ensures that alleles separate during gamete formation? S-B-8-1_Heredity PowerPoint Dihybrid Cross • Mendel repeated his experiment with plants that are bred true for two traits. • He again allowed the F1 generation to self pollinate. • Phenotypic ratio: 9:3:3:1 P X F1 F2 315 108 101 32 Y-Yellow R-Round y-green r-wrinkled http://image.wistatutor.com/content/feed/u2044/Punnet%20square.gif S-B-8-1_Heredity PowerPoint Law of Independent Assortment Mendel’s Explanation • Traits are inherited independently from one another. http://www.palaeos.com/Fungi/Lists/Glossary/GlossaryM.html Modern Genetics • What process ensures that genes are randomly assorted among the gametes? S-B-8-1_Heredity PowerPoint Punnett Squares Punnett Square of Dihybrid Cross Parent Genotype RrYy Gametes’ Genotype Gametes’ Genotype • British biologist Reginald Punnett used a matrix to show the Laws of Segregation and Independent Assortment. • The Punnett Square shows the probability of an offspring having a particular genotype. http://image.wistatutor.com/content/feed/u2044/Punnet%20square.gif S-B-8-1_Heredity PowerPoint Using Punnett Squares Black colored fur (B) is dominant to tan colored fur (b) in dogs. Suppose you cross two hybrid dogs with black fur. What are the possible phenotypes and genotypes of the puppies? What are the expected ratios for each genotype and phenotype? Step 1 Write the genotypes of the parents. Both parents are hybrids or heterozygous for black fur. ♂Bb and ♀Bb S-B-8-1_Heredity PowerPoint Using Punnett Squares Black colored fur (B) is dominant to tan colored fur (b) in dogs. Suppose you cross two hybrid dogs with black fur. What are the possible phenotypes and genotypes of the puppies? What are the expected ratios for each genotype and phenotype? To find the number of different gametes is 2n, STEP 2 where n is the number of heterozygous gene pairs List the different gametes that each parent can make. ♂ gametes ♀ gametes B and b B and b S-B-8-1_Heredity PowerPoint Using Punnett Squares Black colored fur (B) is dominant to tan colored fur (b) in dogs. Suppose you cross two hybrid dogs with black fur. What are the possible phenotypes and genotypes of the puppies? What are the expected ratios for each genotype and phenotype? STEP 3 Make a grid of horizontal and vertical lines. Since the male and female can make 2 different gametes the grid will be 2 x 2. S-B-8-1_Heredity PowerPoint Using Punnett Squares Black colored fur (B) is dominant to tan colored fur (b) in dogs. Suppose you cross two hybrid dogs with black fur. What are the possible phenotypes and genotypes of the puppies? What are the expected ratios for each genotype and phenotype? ♂ gametes STEP 4 ♀ gametes Put the gametes from one parent on the top and the other parent’s gametes on the side. B B b b S-B-8-1_Heredity PowerPoint Using Punnett Squares Black colored fur (B) is dominant to tan colored fur (b) in dogs. Suppose you cross two hybrid dogs with black fur. What are the possible phenotypes and genotypes of the puppies? What are the expected ratios for each genotype and phenotype? STEP 5 Fill in the boxes by copying the row and column headings. B b B b BB Bb Bb bb S-B-8-1_Heredity PowerPoint Using Punnett Squares Black colored fur (B) is dominant to tan colored fur (b) in dogs. Suppose you cross two hybrid dogs with black fur. What are the possible phenotypes and genotypes of the puppies? What are the expected ratios for each genotype and phenotype? STEP 6 Determine the phenotypes of the possible offspring. 1-BB 2-Bb 1-bb } 3-Black colored fur 1-Tan colored fur B b B BB Bb b Bb bb S-B-8-1_Heredity PowerPoint THINK-PAIR-SHARE 1. What would a Punnett square look like for a monohybrid cross of a purple flowered pea plant allowed to self pollinate? 2. What are the genotypic ratios of the monohybrid cross? http://en.wikipedia.org/wiki/File:Punnett_square_mendel_flowers.svg S-B-8-1_Heredity PowerPoint Problems with Two Traits Black colored fur (B) is dominant to tan colored fur (b) in dogs while smooth hair (h) is recessive to wire hair texture (H). Suppose you cross two hybrid dogs with black wiry coats. What are the possible phenotypes and genotypes of the puppies? What are the expected ratios for each genotype and phenotype? Step 1 Write the genotypes of the parents. Both parents are hybrids or heterozygous for black and wiry coats. ♂BbHh and ♀BbHh S-B-8-1_Heredity PowerPoint Problems with Two Traits Step 1 Write the genotypes of the parents. STEP 2 List the different gametes that each parent can make. ♂BbHh and ♀BbHh BH, Bh, bH, bh BH, Bh bH bh ♂ gametes ♂ gametes BH, Bh, bH, bh ♀ gametes S-B-8-1_Heredity PowerPoint Problems with Two Traits STEP 3 Make a grid of horizontal and vertical lines. STEP 4 Put the gametes from one parent on the top and the other parent’s gametes on the side. ♀ gametes ♂ gametes BH Bh bH bh S-B-8-1_Heredity PowerPoint Problems with Two Traits STEP 5 Fill in the boxes by copying the row and column headings. ♂ gametes ♀ gametes BH Bh bH bh BH BBHH BBHh BbHH BbHh Bh BBHh BBhh BbHh bH BbHH BbHh bbHH bbHh bh BbHh Bbhh bbHh Bbhh bbhh S-B-8-1_Heredity PowerPoint Problems with Two Traits STEP 6 Determine the phenotypes of the possible offspring. BBHH BBHh BBHh BbHH BbHH BbHh BbHh BbHh BbHh Bbhh Bbhh BBhh bbHh bbHh bbHH bbhh There is a 9 out of 16 chance that the offspring will have a black wiry coat. There is a 3 out of 16 chance that the offspring will have a black smooth coat. There is a 3 out of 16 chance that the offspring will have a wiry tan coat. There is a 1 out of 16 chance that the offspring will have a smooth tan coat S-B-8-1_Heredity PowerPoint THINK-PAIR-SHARE In guinea pigs, short hair (H) is dominant to long hair (h) and a short tail (T) is dominant to long tails (t). If a hybrid short hair and tail guinea pig is crossed with a long hair and tail guinea pig, what are the expected genotypic and phenotypic ratios? S-B-8-1_Heredity PowerPoint Hybrid parent Step 1: HhTt hhtt Hybrid gametes HT, Ht, hT, ht Step 2: Step 3: Step 4: Step 5: Step 6: Purebred Parent ht HhTt Hhtt HT HhTt Purebred gametes ht Ht hT ht Hhtt hhTt hhtt There is a 1 in 4 chance that the offspring will have short hair and tail There is a 1 in 4 chance that the offspring will have short hair and a long tail hhTt There is a 1 in 4 chance that the offspring will have long hair and a short tail hhtt There is a 1 in 4 chance that the offspring will have long hair and tail • In pea plants Tall (T) is dominant to Short (t) and Purple flowers (P) are dominant to white (p). Cross two individuals who are heterozygous for both traits. • What is the genotype ratio? Phenotype ratio? S-B-8-1_Heredity PowerPoint Complete Dominance Every example so far has been complete dominance, when one allele completely masks another. Sometimes it’s more complicated than that. S-B-8-1_Heredity PowerPoint Codominance • Codominance is when two alleles are expressed simultaneously. They are dominant together. • Ex. People with AB blood type, Roan Horses S-B-8-1_Heredity PowerPoint S-B-8-1_Heredity PowerPoint Incomplete Dominance • Similar to codominance but neither allele is completely expressed. • Example: a red flower and a white flower give rise to a pink flower. (red and white are being expressed incompletely. S-B-8-1_Heredity PowerPoint S-B-8-1_Heredity PowerPoint Sex Linked Traits • Genes located on the X or Y chromosome (usually X) • Males are more susceptible than Females. Why? S-B-8-1_Heredity PowerPoint Example: • In guinea pigs Black hair (B) is dominant to white (b) and Short hair (H) is dominant to long hair (h). Cross a male that is homozygous recessive for fur color and heterozygous for hair length with a female that is heterozygous for both color and length. List the genotype and phenotype ratios. S-B-8-1_Heredity PowerPoint • In human blood typing, A and B are both dominant and O is recessive. If blood typing displays codominance, what would result from a cross between a male with AB and a female with AO. S-B-8-1_Heredity PowerPoint • Hemophilia is a sex-linked genetic disorder on the X chromosome. If a normal male was crossed with a carrier female, what are the possible genotypes of the offspring? S-B-8-1_Heredity PowerPoint X Y X Xh S-B-8-1_Heredity PowerPoint Which sex is most likely to have hemophilia? XX XXh XY XhY S-B-8-1_Heredity PowerPoint