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Wednesday 4-14-2010 Unit 8 Notes: Mendelian Genetics (1) Gregor Mendel Scientist & Monk Studied Pea Plants Determined how traits are inherited Determined how traits are expressed (2) Cross-Breeding Combining sperm + egg Mixing Traits Monohybrid Cross: Cross-Breed 2 organisms Observe only 1 trait Dihybrid Cross: Cross-Breed 2 organisms Observe 2 traits (3) Mendel’s Generations P Generation = Parents F1 Generation = First Offspring F2 Generation = Offspring from F1 Breeding (4) Types of Alleles Dominant Allele: Big Letter Always expressed over the recessive trait. Recessive Allele: Little Letter Only expressed when you have 2. (5) Genotype vs. Phenotype Genotype = Genetic Details of an organism Phenotype = Physical Expression of the genotype (6) Types of Genotypes Homozygous: 2 Dominant Alleles OR 2 Recessive Alleles Heterozygous: 1 Dominant + 1 Recessive Allele (7) Example #1: A) Cross-Breed two homozygous pea plants. One plant is tall, and one plant is short. B) What are the offspring genotypes? C) What are the offspring phenotypes? (8) Example #2: A) Cross-Breed two heterozygous pea plants. Both plants are tall. B) What are the offspring genotypes? C) What are the offspring phenotypes? (9) Example #3: A) Cross two pea plants. One is homozygous recessive and has wrinkly seeds. One is heterozygous and has round seeds. B) What is the probability that they will produce round-seed offspring? C) What is the probability that they will produce wrinkly-seed offspring? (10) Example #4: A) Cross-Breed two rabbits. One is homozygous and black. One is heterozygous and black. B) What are the genotypic ratios? C) What are the phenotypic ratios? (11) Example #5: In rabbits, B is an allele for black coat and b is an allele for brown coat. Write the genotypes for a rabbit that is homozygous for black coat, and another rabbit that is heterozygous for black coat. (12) Example #6: In pea plants, the allele for yellow seeds is dominant to the allele for green seeds. Predict the genotypic ratio of offspring produced by crossing two parents heterozygous for this trait. Draw a Punnett Square to illustrate your prediction. (13) Example #7: In sheep, the allele for white wool (A) is dominant over the allele for black wool (a). If a sheep is white, how could you determine if it is homozygous or heterozygous for white-wool? (14) Example #8: In dogs, the allele for short hair is dominant over the allele for long hair. Two shorthaired dogs are the parents of a litter of eight puppies. 6 puppies have short hair, and 2 have long hair. What are the genotypes of the parents? (15) Example #9: In guinea pigs, the allele for a rough coat ® is dominant over the allele for a smooth coat (r). A heterozygous guinea pig (Rr) and a homozygous recessive guinea pig (rr) have a total of nine offspring. What is the chance that their offspring will have smooth coats? Explain how it could be possible to have 9 offspring, all of which have smooth coats. (16) Example #10: Suppose Mendel crossed two pea plants and got both tall and short offspring. What could have been the genotypes of the two original plants? What genotype could not have been present?