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Patterns of Inheritance: Mendelian Genetics

Patterns of Inheritance: Mendelian Genetics. Artificial selection - true-breeding types (P generation) - hybrids (F1 generation). Gregor Mendel. pea plants. some characters occur in two distinct forms (have 2 traits ). used mathematical analysis to

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Patterns of Inheritance: Mendelian Genetics

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  1. Patterns of Inheritance: Mendelian Genetics

  2. Artificial selection • -true-breeding types (P generation) • - hybrids (F1 generation) Gregor Mendel • pea plants • some characters occur in two • distinct forms (have 2 traits) • used mathematical analysis to • determine ratios in the offspring

  3. Seven Traits that Mendel Studied

  4. 1.Round Seeds X Wrinkled Seeds (P generation) Hybrids of F1 generation 2.When hybrids of F1 self-fertilized: F2generation Mendel’s artificial selection experiments

  5. Mendel’s Conclusions 1. Each form of a character is controlled by a “hereditary factor”. 2. These hereditary factors occur in pairs. 3. Each parent contributes one entire hereditary factor to their offspring.

  6. Genes What are these “hereditary factors”? • Genes may have multiple Alleles • An individual has 2 alleles for a character • The two alleles are located at the same gene • locus on homologous chromosomes • The combination of alleles that one carries for a gene • can be described as Homozygous or Heterozygous • Alleles may be dominant or recessive

  7. Locus for seed shape gene Allele for round seeds Allele for round seeds Homozygous Allele for purple flowers Allele for white flowers Heterozygous A pair of homologous chromosomes

  8. Example: Mendel’s Round and Wrinkled seeds R= round seeds r= wrinkled seeds RR Rr rr homozygous dominant (round) (round) heterozygous homozygous recessive (wrinkled)

  9. 1) Pure round X Pure wrinkled all round (F1) some round, some wrinkled (F2) 2) F1 X F1 Where was the wrinkled allele hiding in the F1 generation plants?

  10. A a a A gamete gamete Mendel’s Law of Segregation

  11. Monohybrid crosses A = purple flowers a = white flowers Aa Aa Aa Aa Predicting the Outcome of Genetic Crosses using a Contingency Table (gametes of parent) AA x aa (gametes of parent)

  12. Purple ? Aa x Aa Genotypic ratio= Phenotypic ratio= • A testcross can help determine the genotype of an individual • with a dominant phenotype: x White aa

  13. A a B b 2 pairs of homologous chromosomes AB Ab aB ab Mendel’s Law of Independent Assortment Alleles of one character are inherited independently of alleles of other characters Gametes

  14. YYRR yyrr P generation RrYy F1 generation YR YR Yr Yr yR yR yr yr F2 generation Dihybrid Crosses Y=yellow y= green R=round r=wrinkled yr YR Yellow round Green round Yellow wrinkled Green wrinkled

  15. Ex. Snapdragons, carnations + Relationships between genotype and phenotype 1. Complete dominance: - 1 allele dominant over the other (ex. A, a) 2. Incomplete dominance

  16. RW RW x RW Incomplete Dominance R= red W= white RR x WW

  17. - Example: A, B, AB, O blood groups } IA IB i 3 alleles Genotype(s) Phenotype 3. Codominance (Multiple Alleles) IAIA or IAi IBIB or IBi IAIB ii

  18. A antigens B antigens A and B antigens Type A Type B Type AB Type 0 Neither A nor B antigens

  19. Other relationships between genotype and phenotype • Pleiotropy: • Epistasis: Example: (coat color in mice) • If C is present, can either • be black or brown B= Black coat b= brown coat C= color c= no color • cc will produce no • color (white) regardless • of “B” alleles

  20. Polygenic inheritance • Environmental influences on phenotype Example: Hydrangea

  21. Study Objectives 1. Contrast the terms character and trait. 2. Define artificial selection. What does it mean when an individual is true-breeding? How does this differ from a hybrid? 3. What did Mendel conclude about heredity from his study of pea plants? 4. Contrast genes and alleles. 5. What are homologous chromosomes? 6. Define homozygous and heterozygous. 7. Define dominant allele and recessive allele. 8. Define genotype and phenotype. 9. Explain Mendel’s Law of Segregation. 10. Construct a punnett square (contingency table) in order to predict the outcome of genetic crosses, expressing genotypic and phenotypic frequencies. 11. What is the difference between a monohybrid and dihybrid cross? 12. When are testcrosses useful? 13. Explain Mendel’s Law of Independent Assortment. 14. Explain the multiplication and addition rules of probability. 15. What is complete dominance? 16. Describe and give an example of incomplete dominance. 17. Describe and give an example of codominance. 18. Explain how blood typing illustrates the idea of multiple alleles. 19. Illustrate crosses relating to the inheritance of blood type on a punnett square. 20. How do blood transfusions work in terms of which blood types can donate to and receive from each other? 21. Describe different ways in which genotype can relate to phenotype, including pleiotropy, epistasis, polygenic inheritance, and environmental influences.

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